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A Strawbale Residential Building Code for the United States

By Bales, Codes and Permits, Issue 62, Straw Bale Construction, Technical One Comment

By Martin Hammer

Mark, Martin, David and  Laura with ICC sign

Mark, Martin, David and Laura with ICC sign

October 14, 2013 marked an historic day in the history of strawbale construction and natural building.  A proposed appendix on Strawbale Construction, and a separate appendix on Light Straw-Clay Construction, were approved at the International Code Council (ICC) Final Action Hearings in Atlantic City, New Jersey.  Both appendices will be included in the 2015 International Residential Code (IRC) for one- and two-family dwellings.  (See sidebar regarding the Light Straw-Clay appendix.)

This has far reaching implications, because the IRC is the basis for the Residential Building Code in virtually every jurisdiction in the United States.  In addition to making permitting easier, obtaining financing and insurance through conventional channels is expected to become much easier, because concerns about structural capacity, fire resistance, moisture issues, etc. are clearly addressed in the code

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Adsorption (More Building Science)

By Bales, Building Science, Issue 62, Straw Bale Construction, Technical No Comments

Building-ScienceBy Chris Magwood

An important concept to understand when considering moisture and building materials is adsorption. Moisture in vapor form infiltrates any and all materials. The surface of most materials will offer individual water molecules an electrically charged attraction, and the water molecules will “stick” to all available surfaces. The makeup of plaster and of straw bales offers a vast amount of surface area for this adsorption. Plasters are full of micro-pores and straw has great deal of available surface area as well as micro-pores in the hollow stems. Together, these materials allow a surprisingly large amount of moisture to safely adsorb onto/into the materials without the water molecules accumulating in sufficient layers to become drops of liquid water. Bales and plaster can hold a remarkable amount of moisture in adsorbed form. “For a 8 pcf (pounds per cubic foot) bale, more than 1 pound of water (approx. 1/12 gallon or 0.46 liters) in vapour form can safely be stored per square foot of wall area” according to John Straube in Building Science Digest BSD-112. This explains why the walls can perform so well as “vapor open” or “vapor permeable” systems.

Straw Bale and Building Science: Growing Up Together

By Building Science, Design, Energy, Issue 62, Plaster, Straw Bale Construction, Technical No Comments

by Chris Magwood

Making Things Air-Tight

Making Things Air-Tight

The straw bale revival of the 1990s reintroduced builders to a pioneer building method that showed remarkable potential for building in a modern context. The nature of the basic components of a straw bale wall system – bales with plaster applied directly to bales – combined several obvious advantages over other wall systems while simultaneously raising some serious questions.

The advantages are familiar to TLS readers: low environmental impact, simplicity and well placed thermal mass. The serious questions and attempts to answer them were the lifeblood of TLS: What about moisture? Air tightness? Cold climates? Humid climates? Longevity of the straw in all these conditions?

There was a lot more going on in the construction world of the 1990s than the straw bale revival. The housing industry was recovering from multiple moisture-related disasters, many caused by overly airtight but under-ventilated homes and/or the use of un-vented “waterproof” exterior cladding systems. The research into these issues, among other factors, led to a rise in prominence of “building science” as a distinct engineering discipline. The straw bale revivalists were extremely lucky to have the attention of some of building science’s leading practitioners, in particular John Straube, who authored several key articles and studies about straw bale walls that were essential to answering the question of why bale walls were so resilient, despite some seemingly obvious moisture concerns.

Simply put, building science attempts to quantify the movement of heat and moisture through building assemblies and help designers and builders to make decisions that lead to structures that adequately deal with the moisture and temperature regimens of their particular climate and use.

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Straw Bale Construction Building Code (2013 IRC Approval)

By Codes and Permits, Issue 62, Straw Bale Construction, Technical One Comment

codes1A more recent post with a more in depth explanation of the ramification of this code appendix can be found here.

On October 14, 2013 the International Code Council (ICC) approved final action RB473-13 as a new Appendix R in the upcoming 2015 version of the International Residential Code (IRC).

The approval marks the latest advance of straw bale construction in the building codes and permitting process.  It is the highest approval to be granted for the construction method and will be adopted by thousands of jurisdictions around the United States in and after 2015.

The process of creating the IRC appendix was spearheaded by Martin Hammer of Builders Without Borders representing the California Straw Building Association, the Colorado Straw Bale Association, the Straw Bale Construction Association –New Mexico, the Ontario Straw Bale Building Coalition, the Development Center for Appropriate Technology and the Ecological Building Network.

Thousands of hours of work have been donated by Martin and various individuals within the straw bale construction community to make this milestone a reality.  We thank all of them for their hard work and look forward to even more widespread acceptance of straw bale building in the construction trades.

A copy of the approved appendix can be downloaded here:

IRC_StrawbaleConstructionAppendix_Approved_10.4.13.pdf

 

Selecting A Natural Hydraulic Lime: What To Look For

By Building Science, Issue 62, Plaster, Technical One Comment

By Michel Couvreux

Thanks to the hard work of a few, Natural Hydraulic Lime has become one of the materials of choice for restoration/preservation projects and natural building construction in the United States.

Suddenly realizing the great potential of NHLs in the US, and feeling the economic hardship abroad, several European manufacturers have begun to latch onto the path opened by Saint-Astier.

Unfortunately, all NHLs are not equal in performance and quality.

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A Straw Bale Construction Wikibook

By Issue 62, Straw Bale Construction, Technical No Comments
By Duncan Lithgow
Straw Bale Building in Holland (Courtesy http://en.wikibooks.org/wiki/Straw_Bale_Construction)

Straw Bale Building in Holland (Courtesy http://en.wikibooks.org/wiki/Straw_Bale_Construction)

I love open content shared with everyone and improved by everyone. So back in 2006 after I was at the International Straw Bale Builders Conference here in Denmark I agreed to collect all the minutes and other documentation for the conference. I made this content into a website I hosted for  a while. But I was not satisfied with the reach of the content, it was only really people who went to the conference who new it existed. So I went to Wikipedia.org and discovered Wikibooks. As the name suggests, Wikibooks, is the the idea of Wikipedia applied to books. So I created a Wikibooks, with the unimaginative title ‘Straw Bale Construction’. The most developed part of the Wikibook is the ‘Technical Studies, Reports and Tests’ section which includes sections on Acoustics, Insulation, Fire Safety, Building Codes and Moisture. The most unusual part is perhaps the section ‘Pushing The Limit’ which looks at Straw Bale domes and arches (see the discussion page for a list of interesting links about that subject).
Then recently I got an email from Jeff at TLS announcing the relaunched website. So I wrote the text above and sent it to him. Quickly Jeff and I saw the potential of wrapping the TLS website around the wikibook. And with the wonders of modern website systems he had it working shortly afterwards. You can see the results at https://www.thelaststraw.org/the-journal/sbwiki/

So if you feel like taking a look, maybe even adding something, feel free. If you click on one of the ‘edit’ buttons you can get started. It’s a great place to add info on your national organization or some research you’ve heard about  – you don’t even need an account. All contributions are licensed for re-use, so if you find (or improve) a section worth publication on paper, let TLS know. And, yes, I keep an eye on all contributions. Write to me if you get stuck [email protected] and I’ll see if I can help.

New Feature!
The Last Straw is now hosting the content of this wikibook here, where it can also be edited and printed as if you are on the wikibooks site.  We encourage people to use this wiki as it appears to be the most comprehensive compilation to date on the web.  If you see something missing, 
incomplete or inaccurate, please participate and make this the most widely used wiki on natural building.
Duncan Lithgow works deep in the guts of Building Information Modeling on Northern Europe’s biggest hospital project, DNU http://www.dnu.rm.dk/.
 

Publication Review: The Straw Bale Alternative Solutions Resource by ASRI

By Book Reviews, Issue 62, Straw Bale Construction, Technical No Comments

SB_ASRThe Straw Bale Alternative Solutions Resource is a document prepared by the Alternative Solutions Resource Institute (ASRI) addressing, obviously, bale construction.  While the goal of ASRI is to “foster and facilitate the use of natural materials and systems in the construction of buildings…” this document is meant to focus specifically on bale construction and how these buildings can be permitted under the Alternative Solutions section of the British Columbia Building Code (BCBC).  For those of you familiar with alternative solutions, or alternative materials as described in the 2009 International Building Code (IBC), this document literally lays out the framework and arguments for the use of bale construction under the alternatives section of the BCBC.  While this is obviously geared toward the British Columbia provincial building code it has as much applicability in the context of other model codes around the world.  The complete and comprehensive nature of this document is a real lifeline for anyone requiring a permit in a jurisdiction with many questions about straw bale construction.

What makes this document most impressive is its coverage of all aspects of building science related to bale construction.  Moisture, plaster materials, fire, structural design, storage of bales, foundations, openings and box-beams are all covered in enough detail to lay a solid enough framework for anyone to permit a bale building.  The comprehensive nature of the document makes it required reading for all architects and engineers working on bale buildings.

While it covers pretty much every aspect that could come into question about bale buildings, it is geared for the seismically active maritime climate of British Columbia.  Expected rainfall in much of B.C. is heavy and they do not mince words when it comes to flashing windows, how far you should keep the bales above adjacent grade, and the role of roof overhangs.  While they do make sure that seismic design is addressed, they do not include any examples or give minimum requirements.  They do expect an engineer to be involved for the earthquake stuff.  One item to note that probably comes from being in a seismically active area is that all of their illustration show mesh being used in the plaster.  This conflicts with many purists view in parts of the world with low seismicity and moderate wind loads.

For the plaster junkies out there, it even has a section that will keep you interested.  It does a great job summarizing the basic concepts that we have come to terms with over the years and how a bale wall with plaster should perform.  As with the rest of the document, they do very well strongly discouraging the use of pure cement plaster due to the wet climate.  However, they do allow for cement-lime in appropriate ratios.

One important thing this document does really well is deal with terminology.  The basic premise first introduced in Bruce Kings book, Design of Straw Bale Buildings, is that the terms we use to categorize bale walls have been inaccurate and are widely misused.  According to this document the two types of bale walls are Structural and Non-Structural (much like all other wall types).  If you are going to use this document, you should get used to not using the terms  “load-bearing” and “post-and-beam” with the building officials.  Either the walls are intended to withstand vertical and lateral loads in excess of holding themselves up, or they are not.  How they are framed or stacked is of less relevance than how they are intended to perform, from a classification point of view.

Other notable items are clear statements such as the following:

  • “A minimum insulative value of R-28 may be used when calculating the thermal performance of a plastered straw bale wall using standard bales.”
  • “Conventional vapour barriers are not necessary or advisable.” (Polyethylene barriers are listed in a section titled Incompatible Materials, which also includes embedded rebar or metal and cement stuccos.)

Due to being in a wet region, one interesting inclusion is the following:

  • “In areas of high rainfall or high relative humidity, consideration should be given to making exterior walls “rainscreen-ready” in anticipation of the need for addition protection.”

In summary, the ASRI solution for bale construction is an impressive, well-written, comprehensive document that all professional practitioners of bale construction should have on their shelves.  While it does not go into detail as much as some books on the subject, it covers everything in a way that shows the authors did their research and left us with a worthy tool in our quiver.  The document is available from the ASRI Website for $25 to help offset costs and maintenance over time, as well as give ASRI a budget for their next projects, which, get this, includes the following:

  • cob
  • rammed earth
  • adobe block
  • light clay
  • earthen plasters and floor systems
  • thermal mass
  • on-site grey-water and black-water treatment
  • alternative healthy electrical technologies
  • passive and active solar integration, and
  • living roof installations

We should support them if they can do something similar for these other building materials and systems.

Birth of the Power Trowel: Pumping Without Spraying – TLS #42

By Bales, Plaster, Products, Straw Bale Construction, Technical, Walls No Comments

This article appeared in TLS issue #42.  This issue includes articles about experimentation and development of bales made from various types of materials.  Articles about methods and equipment for spraying bales with plasters appear in #43 Spraying Earthen Plasters in Colorado), #33 (Stucco Pumping Iron).

by Peter Mack – Ontario, Canada

 

Mud arrives cleanly and directly through the homemade “power trowel” attached to a stucco pump.

Mud arrives cleanly and directly through the homemade “power trowel” attached to a stucco pump.

Very early on in our careers as straw-bale builders, we realized that being able to pump plaster was going to be important if we were going to attempt multiple projects. Bodies and spirits just wouldn’t be able to keep up with endless hand-plastering. So, we bought an ancient pump and started spraying.

Oh, how I remember the days of the sprayer nozzle! The comforting “farting” sound, the reassuring overspray sticking everywhere, plaster in our eyes, noses, lungs, hair, shirts and sometimes ending up on the new roof of the house we were plastering (do not trip while spraying!). The nozzle end was a tiny opening 1/2 to 5/8inch(12-16mm), so if a tiny pebble made its way through the screening and into the nozzle, it could (and did sometimes, much to our chagrin) jam up and create back pressure, even to the point of exploding the hose. Luckily no one has ever been in the way of the hose at the time, but what a sorry mess it makes!

Devising a Solution. We talked often about improving the system. I had read about trowel ends for plaster pumps before, and this kind of fitting seemed like it would be cleaner and easier to use, but it seemed impossible to find one for a large stucco pump. As often happens in life, I set about to make my own. The first step was to buy some new supplies:

  • 8-foot(2.4m) length of 1-inch(25mm) rubber air hose
  • 6-inches(152mm) of 1-inch steel pipe threaded on the outside.
  • 1-inch inline swivel (grease twice daily!)
  • 1.5-inch(38mm) cam lock coupler, NPT threads
  • 2-feet(0.6m) of 3/8-inch(9.5mm) round and square bar
  • various 1-inch hose barbs and bushing reducers
  • aluminum hawk or similar sheet metal

elev1Then I followed these steps:

  • Make a 30-degree (approximate) bend in the 1-inch pipe, leaving an 11inch(280mm) section of the pipe straight at one end. Use an acetylene or propane/ oxygen torch and wind a coupler onto the threads or they will get bent!
  • Grind a flat face roughly 3/4inch(19mm) across along the straight, 11-inch section. This is where the trowel will attach.
  • Grind a slot through the pipe in the flattened section, 3/8-inch(9.5mm) wide by 5-inches(127mm) long, centred five inches from the bend. The plaster will exit through this slot.
  • Place the flat face on the workbench with bend up and weld on four reinforcement bars flush with the face. Use the 3/8-inch square bar. These are necessary to support the trowel attachment, as the trowel material is not strong enough by itself.
  • Weld on the handle. Shape to taste from 3/8-inch round bar, remembering that heavily gloved hands will be trying to hold the handle.
  • Lay out the trowel face. An aluminum hawk makes decent material. Our trowel has very rounded corners and is 12-inches long by 6-inches wide(305x152mm), with a 3/8-inch by 4-1/2-inch(9.5x115mm) slot. Bias the slot towards the end of the trowel by 1/2 to 1-inch to allow closer application to ceilings.
  • Use a drill and saber (jig) saw to cut the trowel out. File off sharp edges.
  • The aluminum is fastened to the steel pipe with polyurethane caulking and annealed steel wires twisted tight with pliers. Our earlier experiments using Lexan for the trowel, attached by 20 machine screws failed, lasting only one or two jobs.
  • The rest is basic plumbing: use Teflon tape on all threads and heavy-duty hose clamps. As we’re reducing the hose down to 1-inch, a full size quick-connect is necessary at the upstream end of the eight-foot hose to allow for proper clean outs.
  • After trying several types of plugs in the open end of the pipe and wasting too much time searching for them at clean out time, we’ve settled into a groove using hand cut plugs made out of styrofoam. They hold just enough that, if the slot plugs up, the pressure pops out the plug. Foam rubber would probably work just as well.

elev2A New and Valuable Tool. Thus was the birth of the power trowel. It worked!  No more overspray!  We won’t kid you…we still make a mess when we plaster, but at least it’s more controlled now. The power trowel needs two operators (or one if that person is truly a power-power troweler, such as Andrew McKay!). One person handles the hose, the other holds the trowel end up against the wall. The trowel end emits a continuous “ooze” of plaster (hence the nickname “Barfing Snake”), and the speed is controlled by the throttle on the pump.

The trowel can be either moved sideways across the wall, or more popularly, up the wall. If you are using an up-and-down motion, the trowel must be held perpendicular to the ground, catching the material being squirted until you can begin applying at the wall’s base again.

There is quite a knack to this grueling job, and the pairs who are quite talented at it actually seem to dance together as they pass the power trowel back and forth, weaving gracefully around scaffolding, rocks, bales and other typical plastering obstacles.

Advantages:

  • fills hollows, good penetration into bales, flattens mud as it applies
  • less clogging because of wider opening, can pass fibre mixes
  • blow off valve works
  • less back pressure, easier on pump engine and workings
  • less loss of paste and water to atomization, resulting in longer working times
  • no more overspray on windows, ceilings and people (although we do still drop a bunch on the ground/floor)

Disadvantages:

  • overhead areas difficult
  • does not quite reach ceiling, trowelers often have to push the mud up the last three or four inches(75100mm)
  • occasional air pockets between coats
  • somewhat more physical effort for the nozzle person.

We still sometimes reminisce about the old days of the “farting” spray, and will occasionally bring it out of the closet and take it for a test drive; once a friend wanted to record it for a CD, but do we really miss it? Not a chance! The power trowel has made life as plasterers easier, cleaner and quieter.

 

Peter Mack is a full-time bale builder and a partner in Camel’s Back Construction. He is co-author of the book Straw Bale Building (New Society Publishers). Contact: Peter Mack <[email protected]> www.strawhomes.ca

Finishing Bale Walls with Siding – TLS #57

By Bales, Building Science, Design, Plaster, Straw Bale Construction, Technical, Walls, Water 2 Comments

This article appeared in TLS #57.

Loose Strings: Technical Discussions
by Jeff Ruppert – Colorado, USA
T e c h T i p s

A little known fact in the bale building realm is that a handful of people scattered across different continents have experimented with the idea of finishing their bale walls with wood or some type of manufactured siding. The technical term for siding over a bale wall assembly is a “rain screen.” The use of a rain screen (sometimes referred to a “multiple defense assembly”) on a bale wall plays the role of keeping rainwater off of the bale portion of the wall. This is in contrast to the standard way of finishing a bale wall with plaster and allowing moisture to come into contact with it on a regular basis (also referred to as “faceseal” walls). In fact, almost all of the literature to date on bale-wall construction makes the assumption that they are faceseal assemblies.

In this article, we are going to take a look at the pros and cons of in-stalling siding over a bale wall. To some people the idea of not having a plaster finish on a bale house would seem weird, mainly due to aesthetic reasons. However, for those who have chosen to use siding, aesthetics take a backseat to function due to high rates of rainfall throughout the year, as well as constant high humidity. The option of allowing bale walls to even get wet in the first place is not an option and therefore other systems must be considered.

For those of us who live in drier climates, the consideration of moisture is not as dire, therefore giving us more choices. However, doesn’t the siding option make sense if you are concerned about moisture at all? If you would like to design a building with mixed finishes, such as a combination of plaster, masonry and siding, this would open up the opportunity to include bale walls as an option on those projects. In fact, by installing a rain screen over bale walls are we not greatly reducing the potential for moisture damage, as David Eisenberg puts it, by “designing problems out of the project” from the start? We will explore these issues and hopefully offer you another choice in your search for solutions.

Rain Screens
In the old days, a rain screen was simply an exo-barrier that was attached to a building to catch rainwater and shed it before it could hit the structure behind it. The Norwegians titled this approach the “open-jointed barn technique,” since originally it was used in conjunction with the construction of barns1.

With tighter construction and newer forms of finishes, the technology of rain screens has evolved into a science. One of the advantages of using a rain screen on a bale wall is that, no matter
how you do it, it will probably add a significant layer of protection that would otherwise not exist. This assumes that you do not install the siding to accidentally direct water into the wall. The potential exists for this to happen, so just like any other type of finish, pay attention to the details!

Siding over bale walls

Siding over bale walls

No matter what type of wall you build, the driving forces of moisture will be:

  • Air pressure difference (gradient)
  • Gravity
  • Surface tension
  • Capillary action
  • Rain drop momentum.

The dominant force acting on your walls will be the difference in air pressure across the siding itself.  As the wind blusters around your house, there are pockets of less and more pressure ever changing within and around your wall assemblies. The main goal is to minimize any pressure differences so water is not accidentally driven into the wall assembly. By minimizing pressure differences, the main force acting on nearby moisture will then be gravity, drawing water down to the ground where it belongs, before it reaches your bales.

In order to equalize pressure, an air gap behind the cladding (siding) needs to be well ventilated to the atmosphere. This can be achieved through different methods, but whatever you do, make sure not to create a gap for wind to blow rain behind the cladding. This means providing ventilation behind the siding so air can pass through easily, but including a barrier at the points of ventilation to keep wind-driven rain from entering.

The advantages of using a rain screen are:

  • Adds another option for finishing bale walls (aesthetic),
  • Keeps moisture completely off the bale portion of the wall assembly,
  • Provides replaceable/changeable finish,
  • Has low or no maintenance (depending on material),
  • Uses local materials in northern climates near forested areas.

The disadvantages of using a rain screen are:

  • Plaster finish is not an option on a bale wall,
  • May not be as durable as some types of plaster,
  • Materials may not be sustainable or even available in your area,
  • Aesthetic of siding may not match your project.

Rain Screen Concept on Bale Walls

It is important to remember that no matter how we finish bale walls, they must be sealed with plaster. This means that even if we choose to use a rain screen, we must apply at least one coat of plaster. One way to install siding on bale walls is to first install nailers for the siding. These can be in the form of 2-in.x2-in. wood strips attached to the sill plate and beam at the top of your bale wall.
We recommend attaching the nailers before stacking the bales, but you can do it afterwards if you like. Once the nailers and bales are in place, one coat of plaster is applied between the nailers. A rough coat of plaster over the bales is all that is necessary. Little or no troweling is required because no one will ever see the results. After plastering, building paper is stapled to the nailers and the siding is then installed, leaving a gap behind the paper for ventilation and drainage.

One issue of concern with this method is the gaps that can occur between the plaster and nailers as the nailer wood shrinks over time. These gaps can allow air to ?ow in and out of the bale wall, creating a loss of insulating value, as well as a path for insects and/or rodents. Extra care and/or the application of caulk can take care of these gaps. Also, these gaps can be eliminated if the nailers are installed after plaster is applied. Whatever you do, be sure that a gap remains between the back of the siding and the plaster.

This is but one way to install siding on to a bale wall. There are variations to this concept, but the goals remain the same – keeping rainwater and back-splash off your bale walls. Pay attention to the details and remember the forces that are acting on water that comes into contact with your walls. Holding these basic concepts in mind will help you design your wall system. And most important, do your homework first!

Happy wall building!

Resources
1. Rainscreen Cladding: A Guide to Design Principles and Practice.Anderson, J.M. & Gill, J.R. Butterworth-Heinemann, 1988.
www.shildan.com/Rainscreen/History.htmlhttp://irc.nrc-cnrc.gc.ca/pubs/ctus/17_e.htmlwww.greenhomebuilding.com/pdf/RainScreen.pdfwww.cmhc-schl.gc.ca/en/inpr/bude/himu/coedar/loader.cfm?url=/commonspot/security/get?le.cfm&PageID=70139

Ed.Note: Jeff encourages TLS readers to send in questions and comments to The Last Straw. There may be outstanding issues that builders are dealing with that most laypeople may not aware of. There are always many questions from people new to straw-bale construction. With this in mind, this column is offered and intended to encourage everyone to educate themselves to the fullest extent regarding building construction, and we are here to help in any way we can. This forum endeavors to offer the best of our knowledge, with no claim to its completeness, but to the spirit of bale building as a continuing evolution of one form of habitat within the larger realm of natural building. We offer this forum for dialogue, with no implication of being right or wrong. This forum is for you, the learner, artisan and teacher.

Jeff Ruppert, P.E., Principal, Odisea LLC, Ecological Building, Engineering and Consulting, P.O. Box 1505, Paonia CO 81428, 970.948.5744  <[email protected]> www.odiseanet.com
Jeff has been in the construction trades for over 25 years, beginning as a laborer and draftsman on his father’s construction projects. He has spent many years working on construction projects he designs, and is a licensed engineer in Colorado.

Newsflash! Straw-bale Infill Meets U.S. Building Codes – TLS #54

By Building Science, Community, Design, Straw Bale Construction, Technical, Uncategorized No Comments

codes1This article originally appeared in Issue #54.  This issue includes a table of straw-bale building codes, guidelines and mandates in the U.S., and links to straw-bale codes, guidelines and supporting documentation; and an extensive review of the status of straw-bale codes and permitting throughout the world.

by Sigi Koko – Pennsylvania, USA

The bottom line is that yes, using straw bales for non-loadbearing infill walls meets existing building codes for both residential and commercial structures throughout the United States. Why is this true? Because building codes are not written to exclude new or alternative construction materials and methods. Rather, each building code begins with an inclusive statement such as the following from the CABO 95 Preface:

“…there are construction materials and practices other than listed in this code which are adequate for the purposes intended. These other methods represent either seldom-used systems or performance-type systems which require individual consideration by the professional architect or engineer based on either test data or engineering analysis and are therefore not included herein.”

The intent of building codes to ensure that materials are used safely and suitably, not to limit the use of appropriate materials. The burden of proof is to demonstrate that an alternative construction method meets the intent of the building code for durability, effectiveness, and safety (including fire resistance). This means showing how straw-bale infill wall systems meet the requirements of the building code for insulation value, flame spread, smoke development rating, and fire rating. Demonstrating compliance with the building codes is possible thanks to many pioneers that have dedicated time and money to sponsor third-party ASTM (American Society for Testing and Materials) tests. The results of these tests show that straw-bale wall systems not only meet the building code but, in most cases, surpass the intent of the code compared to standard stud-and-drywall construction.

Several states and counties throughout the U.S. have adopted building code amendments that specifically address straw-bale construction, though most regions do not yet include such provisions. Obtaining a building permit for straw-bale infill in regions without a specific building code is not impossible, but rather entails a non-standard process. The question is not whether you can get a building permit for infill strawbale, but rather how to best communicate with local building officials that strawbale is a viable method of construction that meets the existing building code.

David Eisenberg has written extensively and with great eloquence about how to communicate effectively with building officials, and I encourage anyone wanting more detailed information to review his writings on the topic. I have used the following strategy with success:

1) Schedule a pre-submittal meeting with the permitting official to communicate your intentions to build with strawbale. If they are not already familiar with straw-bale construction, provide printed information and additional resources. (Don’t overload with information unless it is requested; like all busy people, building officials are less likely to review a daunting pile.) Bring to the pre-submittal meeting:

• drawings of the proposed building

• an overview of straw-bale construction (I use “House of Straw: Straw Bale Construction Comes of Age” by the US Department of Energy, available at www.eere.energy.gov)

• copies of ASTM testing data (fire-related ASTM tests are at www.dcat.net)

For the final permit submittal, my experience is that stamped structural drawings greatly facilitate the speed and ease of the permitting process.

2) Remember that your building official is your ally not your adversary, and has the same goal as you: to ensure that what gets built is safely built.Acknowledge your common interest for occupant well being and safety. You will create connection instead of confrontation and open a dialog on how to achieve your common goal.

3) Be informed or hire an advocate that has experience in straw-bale construction, including how to build appropriately in your climate. The building officials will generally have more confidence in your project when they know someone on your team fully understands this non-standard construction technique. At a minimum, be prepared for the following common questions:

  • How does your wall system handle liquid water and vapor?
  • What is the fire rating and smoke development rating of the wall system?
  • Will the straw bales attract pests, such as termites and rodents?
  • What is the insulating value of strawbale?
  • How is electrical and plumbing installed?

I have to date not experienced any delays during the permitting process using this method of interaction with building officials. Increasingly, I find that building officials already possess some level of knowledge about straw-bale construction, which was not the case in this region of the country (Mid-Atlantic states) even five years ago.

Finally, I would like to address the issue of adopting existing codes and details in different climates. I design structures in a wet, humid climate with hot summers and cold winters. However, many of the now-standard straw-bale details have mostly developed in arid and temperate climates that are not necessarily durable in this mixed climate. For example, I do not recommend using rebar inside a straw-bale wall in a humid climate, since the cold metal creates an artificial dew point inside the straw wall. The result is elevated moisture around the rebar, which can lead to rotting the straw over time. Instead, I recommend external pinning or using materials that are “warm,” such as bamboo. Similarly, pea gravel at the base creates an artificial dew point, as well as creating a thermal break along the entire base of the wall. My point is not that the originally developed details are inadequate, but rather that they are specific to an arid climate. So when adopting codes and details in different regions with different climatic concerns, ensure that what you propose will perform durably in your climate.

Sigi Koko, the founding principal of Down to Earth, a design and consulting firm specializing in natural building, has obtained construction permits for many straw-bale buildings in her area. With a Masters of Architecture and several years of in-the-field construction experience, she has developed written specifications and architectural details for straw-bale and cob construction. www.buildnaturally.com

Build Your Own Simple Bale Wall Moisture Sensor – TLS #57

By Building Science, Plaster, Products, Straw Bale Construction, Technical, Walls, Water No Comments

This article appears in issue #57 of TLS.  There have been other articles about moisture sensors in recent years.

drillby Habib John Gonzalez – British Columbia, Canada

This article appeared in a slightly longer version in TLS#22/Spring 1998.

Here are the simple steps and materials needed to build your own bale wall moisture sensor:

1. Determine what depth of the bale you want to monitor and cut the 3/4-inch PVC pipe to that length.

2. Make the white pine sensor disk 1/8-in. thick to fit snugly into one end of the pipe.

3. Solder two lengths of telephone wire to two pairs of small bolts. One end of the pair of wires is bolted to a PVC pipe cap so the tips will protrude from the finished interior wall. The other end of the wires will be bolted to the sensor disk.

4. Use epoxy to glue the disk to one end of the pipe; run the wires through the pipe and fasten the other pair of bolts to the interior wall end cap. Glue the cap to the pipe.

5. Glue a perforated pipe cap over the sensor end of the pipe.

sensor6. The sensor is ready for installation in the bale wall.

7.The TimberCheck moisture meter is available from www.leevalley.com

8. A number of bale wall moisture studies were sponsored by the Canadian Mortgage and Housing Corporation (CMHC). You can get a summary of all of the CMHC moisture work on their web site www.cmhc-schl.gc.ca/publications/en/rh-pr/tech/dblist.cfm?mode=year.  Scroll down to the bottom of the list for 00-103 (year 2000, document 103) on straw-bale moisture monitoring.

schematic

 

 

 

1. Outer end-cap
2. Perforated PVC pipe
3. Wood disk with screws
4. Wires
5. PVC pipe
6. Inner end-cap
7. Screw contacts

Earth Plastering Guidelines for Finishes – TLS #43

By Bales, Building Science, Plaster, Technical, Walls One Comment

This article appeared in TLS #43.

by Gernot Minke – University of Kassel, Germany

Note: This article is excerpted from Earth Construction Handbook (by Gernot Minke, WIT Press, Southhampton, Boston, 2000) which contains further information about weather protection, physical and mechanical properties of clayey soils, treatments and additives and modern earth construction techniques worldwide.

blocks1) General. Earth plasters mainly consist of sand and silt with only as much clay as is necessary (usually between 5% to 12%) for developing their adhesive and binding forces. It is difficult to state what the proportions of an ideal earth plaster should be, because not only does the proportion of clay, silt and sand influence the properties, but also the grain size distribution of the sand fraction itself, the water content, the type of clay, the method of preparation and the additives. In order to test the appropriateness of earth plasters, samples with varied compositions should be tested. Earth plasters stick very well not only on earth surfaces, but also on brick, concrete and stone surfaces, if the surface is rough enough.

2) Preparation of substrate. As earth plaster does not chemically react with the substrate, the surface has to be sufficiently rough in order to develop a good physical bond. A good method of getting a strong bond is to wet it sufficiently until the surface is soft, and than scratch diagonally patterned grooves with a small rake or a nail trowel. In order to ensure that the plaster adheres better, it is also possible to use latching in the form of galvanised wire mesh, plastic mesh, reed mats, and such on the substrate before plastering.

3) Composition of earth plaster.

3.1 General. In order to get earth plaster free of shrinkage cracks, the following points must be kept in mind:

  • The earth should have enough coarse sand.
  • Animal or human hair, coconut or sisal fibres, cut straw or hay should be added (however, too much of these additives reduce the ability of the plaster to adhere to the substrate).
  • For interior plastering, sawdust, cellulose fibres, chaff of cereal grains or similar particles can also be used as additives.
  • In order to develop enough binding force, the adhesive forces of the clay minerals should be sufficiently activated by adequate water and movement.
  • When the plaster sticks to a sliding metal trowel held vertically, yet is easily flicked away, the correct consistency has been achieved.

In order to test the characteristics of an earth plaster, a simple adhesion test can be carried out. The plaster to be tested is applied 2cm(3/4-inch) thick to the flat surface of an upright burnt brick. The plaster has to stick to the brick until it is totally dry, which might take two to four days.

If it falls off in one piece by itself, as seen in the left sample of fig. 3-1, it contains too much clay and should be thinned with coarse sand. If it falls off in portions after the sample is hammered on the floor like the second sample in fig. 3-1, then it has insufficient binding force and should be enriched with clay. If the plaster sticks to the brick but shows shrinkage cracks, like the third sample in fig. 3-1, it is too clayey and should be slightly thinned with coarse sand. However, it can be used without thinning as the first layer of a two-layer plaster. If the surface shows no cracks and the plaster does not come off when hammered, as in the fourth sample in fig. 3-1, then the sample might be adequate. In this case, it is advisable to make a larger test about 1x2m(40×80-inches) high on the actual wall. If shrinkage cracks now occur, this mixture needs either to be thinned with coarse sand or mixed with fibres.

3.2 Exposed exterior earth plasters. Exposed exterior plasters have to be seasonably weather resistant or must be given perfect weatherproof coating. It is important in cold climates that the plasters together with their coating have a low vapour diffusion resistance, so that water condensed in the wall can be easily transported to the exterior. The exterior plaster must be more elastic than its ground in order to meet thermic and hygric influences without cracking. In general, for cold climates, an external earth plaster is not recommended unless sufficient roof overhang, plinth protection and good surface coating can be assured.

Since plastered wall edges are very easily damaged, they should either be rounded or lipped with a rigid element. In extreme climates when the elasticity of large expanses of flat plaster is insufficient to cope with the influences of weather, vertical and horizontal grooves filled with elastic sealants are recommended.

table3.3 Interior earth plasters. Interior plasters are less problematic. Usually they create no problem if they have fine shrinkage cracks because they can be covered with a coat of paint. Dry earth plaster surfaces can be easily smoothed by wetting and being worked upon with a brush or felt trowel.

If the surface of the walls demands a plaster thicker than 15mm(5/ 8-inch), it should be applied in two layers, with the ground layer containing more clay and coarse aggregates than the second layer. If the ground layer gets shrinkage cracks, it is not problematic, but could actually help by providing a better bond to the final layer of plaster.

Adding rye flour improves the surface against dry and moist abrasion. The author has proved by testing that this resistance can also be built up by adding casein glue made of one part hydraulic lime and four to six parts fat-free quark, borax, urea, sodium gluconate and shredded newspaper (which provides cellulose fibre and glue). The mixes in the accompanying chart worked well.

Lime reacts with the casein within the fat-free quark forming a chemical waterproofing agent. A similar reaction is obtained with lime and borax (which is contained in the shredded newspaper). Sodium gluconate acts as a plasticizer so that less water needs to be mixed for preparation (thereby reducing the shrinkage). Urea raises the compressive and the tensile bending strength, especially with silty soils.

Waste paper shreds lead to better workability and reduce shrinkage. The mixes B, C and E showed best workability. When using mixes A and E, it is preferable to first mix the casein glue and the shredded newspaper together with the water, and then, after an hour, add earth and sand.

With all mixes, it was found that the final smoothing of the surface, which was done by a felt trowel, was best done after several hours or even a day.

4) Guidelines for plastering earth walls. As pure earth plaster does not react chemically with the substrate, it might be necessary to treat the substrate suitably so that sufficient bonding occurs. The following guidelines should be kept in mind:

1. The surface to be plastered has to be dry, so no more shrinkage occurs.

2. All loose material should be scraped off the surface.

3. The surface should be sufficiently rough and, if necessary, moistened and grooved or the mortar joint chamfered, as described in section 2.

4. Before plastering, the substrate should be sufficiently moistened so that the surface softens and swells and the plaster permeates the soft layer.

5. The plaster should be thrown with heavy impact (slapped on) so that it permeates the outer layers of the ground and also achieves a higher binding force due to the impact.

6. If the plaster has to be more than 10-15mm(3/8-5/8-inch) thick, it should be applied in two or even three layers in order to avoid shrinkage cracks.

7. To reduce shrinkage cracks while drying, the mortar should have sufficient amount of coarse sand, as well as fibres or hair.

8. To improve the surface hardness, cow dung, lime, casein or other additives should be added to the top layer.

9. In order to provide surface hardness and resistance against wet abrasion, the surface should be finished with a coat of paint[Editor’s Note: breathable paint].

10. While using plasters, the change of physical properties caused by additives and coatings should be kept in mind especially with respect to vapour diffusion resistance.

decorative5) Sprayed plaster. A sprayable lightweight earth plaster with high thermal insulation containing shredded newspaper was successfully developed by the author in 1984. This plaster can be applied in a single layer up to 30mm(1-1/4-inch) thick using an ordinary mortar pump. In order to get a shorter curing period, some high-hydraulic lime and gypsum was added to the mixture.

balls6) Thrown plaster. Fig 6-1 shows how a traditional African technique, which consists of throwing earth balls on a wall, has been adapted. Here, this technique is used on a wood-wool board for a winter garden wall. In order to increase the adhesion, bamboo dowels were hammered halfway into the board.

7) Wet formed plaster. As loam plaster retains its plastic state for a long time and is not corrosive to the hands like lime or cement plasters, it is an ideal material for moulding with the hands. Fig. 7-1 shows an example of an exterior loam wall stabilised by a lime-casein finish.

Professor Dr.-Ing. Gernot Minke is a professor at Kassel University and a consultant structural engineer since 1967. He has a keen interest in earthen structures and low-cost, low-impact housing. He numerous publications include the Earth Construction Handbook (WIT Press, Southhampton, Boston, 2000). Contact: <[email protected]>

This article was submitted by Friedemann Mahlke, a student of Dr. Minke and a straw-bale builder and researcher. Contact <[email protected]>

Lime Mortars DVD Review

By Plaster, Products, Technical, Walls One Comment

 

What is the ratio of your mix?  Let your sand tell you!

This article is original content and has not yet appeared in the printed version of The Last Straw.

St. Astier Natural Limes, a producer of hydraulic lime products from France, is offering a set of DVD videos called The Master Stroke DVD Tutorial Series.  The Master Stroke is a 4-disc series beginning with lime mortars.  Other discs cover plastering and rendering with lime, and building and pointing with lime.  In this article we will review the first in the series, Making Lime Mortars.

The content of the DVD is laid out very clearly and is easy to follow.  The quality of the video is very polished. The main purpose of the DVD is to show the construction worker how to create a consistent, high-quality mortar or render.  Tips include how to properly keep your sand dry, how to measure each bucket of sand, etc.  But there was one piece of information that really make this video important.  Nearly half of the video is dedicated to the concept of the sand void ratio and how it affects your mix.

Have you ever wondered where the ratios we use for our mixes come from?  This video explains how they are derived.  Without going into too much detail, the ratio of sand to lime is determined by finding the void ratio of your sand.  Once you know how much air is between the grains of sand you can find the volume of binder.  If you use too much binder, the sand particles will be far apart, separated by water and lime.  If you use too little lime you are not filling all the voids with lime and you will have pockets of air and water.  The perfect ratio is one that fills all the voids and leaves little room for air or water.  Once you know this ratio, based on your sand, you can then adjust the ratio to achieve your desired results.  Don’t think you can just figure this out on your own through this article.  There is a proper way to do this, and each step is clearly defined in the video.

To know the proper ratio of sand to lime (or any other binder – clay, cement, gypsum, etc) is like an enlightenment for most of us.  Have you ever wondered why the code says 4:1:3/4 (sand:cement:lime), or why your friends used 1:2:9 (cement:lime:sand)?  Now you don’t have to guess.  This video will teach you how to properly measure the void ratio of your sand and the ratio of sand to binder.  It will become apparent that the mix your friends are using on their project has little bearing on your mix.

Mortars, renders and plasters all folow the same ratio and mixing concepts.

Mortars, renders and plasters all folow the same ratio and mixing concepts.

Learning how to derive the ratio of sand to binder is obviously very valuable.  The rest of the video walks you through the measuring and mixing process, showing how a professional would prepare his or her mortar.  After being a sub-contractor and mixing thousands of batches of plaster, this video would have been great as a tool for estimating.  In my mind it creates a baseline for high-quality that a builder can use to determine costs.

In summary, I would say buy this video!  It can be purchased at the link above for $39.  From novice to professional, you will find value.  Good luck.

This review is intended to be objective.  No compensation of any form has been accepted in connection with this article.

Bale Wisdom – Bale Buying 101

By Bales, Straw Bale Construction, Technical No Comments

This article was originally printed in the 2003 Resource Guide

Compiled and updated by Joyce Coppinger from the writings of Judy Knox, Kim Thompson, books on strawbale, and US Department of Energy.

communityIn most cases, it is advisable to find a source for your bales early on in your project planning as the size of the bales may influence how you lay the bales in the walls or bale orientation, wall spans, ceiling heights and other design considerations. And, be sure that the bales are stored under cover, preferably in a barn or storage building, until they are taken to your construction site.

Twenty Tips on Bale Buying
1. Purchase bales following the harvest when bales are usually inexpensive and abundant. You may need to contact local farmers during planting season about growing and custom baling.
2. Make sure the bales are stored high and dry from the time they come out of the field until they are installed in your building’s walls.
3. Don’t rely on hearsay about the size and condition of any bales you might buy. Check out the bales yourself.
4. Bales should be “bright” and dry with no sign of moisture, mildew or mold.
5. Test some portion of the bales you select to make sure they have always been dry.
6. Bale moisture content should be 14 percent or less. (Use a digital probe or moisture meter.)
7. An ideal proportion of a bale in size is twice as long as it is wide. This simplifies maintaining a running bond in courses.
8. Commonly available bale sizes: two-string, 14 inches(36cm) high x 18 inches(46cm) wide x 35-40 inches(91-96cm) long, weighing about 50 pounds(40 kg); three-string, 16-17 inches high x 23-24 inches wide by 42-47 inches long, weighing about 75 pounds(60 kg).
9. Try to get bales of equal size and length. If they do vary in length, as many will, lay ten bales end-to-end. Measure this entire length and then divide by ten. This is the average bale length to use for planning and designing purposes.
10. Bales should be free of weeds and mostly free of seed heads.
11. Wheat, oats, rye, barley, rice or flax are all good bale materials. Some grasses can be used for bales (switchgrass, for example). Do not use alfalfa or other brittle stemmed plants. Other materials are now being baled, such as paper and cardboard (See TLS #42/New Systems).
12. Look for thick, long-stemmed straw. Straw of 3-4 inches or 7.5 to 10.2 cm is not recommended. The stem length will vary depending on the type of baling machine used.
13. The R-value and other properties of your bale (tensile strength, moisture content, burnability, for example) will vary depending on the type of plant or crop residue used.
14. Dealing directly with farmers may give you more say about bale quality and consistency.
15. Expect to pay extra for transportation and storage.
16. Wholesale brokers offer direct access to the bale supplier and often offer commercial transportation.
17. Retail outlets and feed stores are the easiest source to access, you will probably pay more for your bales than those you buy from a broker or directly from the farmer.
18. Bales must be tightly tied with durable material, preferably 240-lb. knot strength polypropylene (usually won’t decompose) or hemp twine or 16-gauge galvanized baling wire (usually won’t rust). Avoid bales tied with traditional natural fiber baling twine (sisal, for example).
19. When you lift the bale, it should not twist or sag. The flakes (sections within some bales) should not pull apart easily.
20. Make sure the bales are uniform in size (as much as possible – there will be some variance) and are well compacted.

Bale Orientation:
Bales can be laid flat (strings between courses, the wider side laid parallel to the ground). When the narrower of the two sides is laid parallel to the ground, the bale is being laid “on edge.” Bales can also be placed on end in small spaces where vertical stacking is required. The recommended placement for two-string bales is flat. Three-string bales can be used either flat or on edge. The R-value for two-string bales is believed to be approximately the same regardless of placement.
Flat placement provides maximum wall thickness and is more stable during construction. It also offers greater resistance to vertical compression. If a wire or string fails, expansive forces will be parallel to the wall and will be contained by the surrounding bales. Notches up to 5 inches can be cut into bales without severing a string or wire. Beveled bales can be more easily created for filling in the eaves of a peaked roof.
Placing bales on edge creates more wall height and bales can be cut parallel to the strings for placing windows. It also makes attaching stucco netting easier, because it can be fixed directly to the strings.

Bale Storage:
Storage should be off the ground, preferably in a barn or storage building. If outdoors, preferably on pallets, to keep ground moisture from being absorbed, and covered with high quality tarps to keep the bales dry. The tarps should cover each side of the stack of bales by at least one bale. The stack should be crowned (built to a peak at the top) to keep water from standing on the tarps and perhaps leaking into the middle of the stack through cuts or holes in the tarps. Best if the top row of bales (around the perimeter of the stack of bales) has a slight overhang to help protect the sides of the stack.
Inexpensive tarps and rolls of plastic are not preferred as they may tear or puncture easily, making moisture penetration into the bale stack more likely. Covering the bale stack with plastic sheeting and then covering the sheeting with tarps could help keep moisture away from the bales. Anchoring the bales securely is not always easy, but it’s very important, especially to protect the bale stack from strong winds and storms. Weighting the bale stack down with old tires, cement blocks, or logs tied to the end of a rope and attached to grommets in the tarps’ edges is a good method for anchoring the sheeting and tarps.

Handling Bales:
Most bales are easy to move around and stack. However, two people lifting and moving the bales will speed up the work and reduce body strains. Baled material can be scratchy and itchy as well as dusty – so long-sleeved shirts and pants, dust masks and gloves should be worn. Hay hooks can be helpful.
Lifting and throwing bales can be eased by using your body weight and the momentum of a swing or toss. Probably best not to try to just muscle them around when moving and lifting the bales. Use a wheelbarrow or large wheeled dolly to help with bale moving and, in some instances, heavy farm or construction equipment such as a small crane, a tractor with lift, could be helpful.
Bales can be used for stairs and as scaffolding – but caution is the word, as baled material can be slippery. And, keep loose straw raked and stacked away from the bale walls and the construction area, as it is highly flammable and dangerous underfoot.

Straw-bale Sound Isolation and Acoustics – TLS #53

By Building Science, Design, Sound, Straw Bale Construction, Technical, Walls One Comment

This article appeared in TLS #53.  The topic of this issue is Moisture.  It contains an extensive article about Moisture Basics and Straw-Bale Moisture Basics (by John Straube, edited by Bruce King)  it also includes articles on moisture meter accuracy, moisture sensors, seismic resistance, and plaster testing.

by Rene Dalmeijer – The Netherlands

In June 2003, Jasper van der Linden, a building engineering student at the Eindhoven Technical University, Eindhoven, The Netherlands, tested the sound isolation of an earth-plastered straw-bale wall. Rob Kaptein of RAMStrobouw and I assisted in carrying out the test. The test was executed in a true acoustic test chamber according to ISO 140-3. We were able to execute a consistent test giving a good indication of how well a plastered straw-bale wall retards sound.

Based on the outcome of the test, it is to be expected that a reasonably well-designed and built straw-bale wall without acoustic defects (like protruding post-and-beam members) will perform in the region of 53dB and upwards (55dB with A weighting; “A-weighting” means the impedance is corrected to approximate human hearing sensitivity, which varies depending on frequency). The 2dBA increase in performance when compared to the test is mainly because we used very thin (worst case) plaster thickness in the test sample. Normally earth plaster finishes would be thicker. This puts the performance of a straw-bale wall at more or less the same level as a decoupled brick cavity wall and even exceeding it in the critical low-frequency region.

Most everyone who has been in a straw-bale building has had the sensation that interior sounds somehow seem louder, because interior sounds become more distinct for not being drowned out by background noise coming from the outside. This is a clear indication that straw-bale walls work very well as an acoustic insulator. Normally built structures depend on high mass for good sound insulation. But there is also another way of achieving good sound insulation, which depends on a damped cavity surrounded by two not-sostiff membranes with sufficient mass. A straw-bale wall, specifically with earth/clay plasters, is an excellent example of this alternative way of achieving good sound insulation, as the test result clearly illustrates.

The Test

The test was executed in the acoustic lab of the Eindhoven Technical University. The test and test facility is according to ISO 140-3 which is to test the sound isolation of building aperture of two acoustically separated chambers (the test sample is placed in an aperture between the chambers). Although I am aware of the limitations of the test facility for testing a wall system, we have endeavored to make this test as accurate and as representative as possible. The aperture’s size (ISO 140-3 std) is 1.88m2 /20 ft2. The tested straw-bale wall section had the following configuration:

  • Two-string (460mm wide building quality bales laid flat density 120-130kg/m3)
  • Earth/clay straw plaster 25mm and 35mm (intentionally asymmetrical cover)
  • No reinforcing plaster netting or mesh or any form of pinning

table1The chosen sample structure was to be as representative as possible of a normal earth/clay plastered straw-bale wall structure as used by the experienced straw-bale builder Rob Kaptein of RAMstrobouw. Rob was also responsible for manufacturing the test sample. The graph and table summarize the test result.

[Rene’s comment on the measured performance: The result can be expressed as 53dB according to A-weighting. Actually expressing the sound isolation value in one number (i.e., 53BA) is a simplification. In actual fact, giving the performance at each of the various frequencies is much more meaningful.]

Generally this is done at either one octave intervals (1/1oct) or at one-third octave intervals (1/3 oct), the last giving even more detailed information.The graph and table show both measurements (not A-weighted). The dip at around 250Hz is due to the transition between the masws and damped cavity odes of operation of the test sample and should be largely disregarded as part of the vagaries of a test.

The 53dBA test result might seem low but in fact is very good. Most conventional wall systems including a brick cavity wall with much higher mass have a lower performance. Specifically interesting to note is the 2-3dB better performance at very low frequencies of the straw-bale test sample when compared to brick-wall systems. Nearly all wall systems, including stick frame, are able to sufficiently subdue high-and mid-frequency sound, but low-frequency sound is problematic. In practice, better performance at low frequencies is worthwhile because it means that the ever-present background noise in suburban areas is perceptibly reduced.

Recipe for Straw-bale Wall Acoustic Isulation

Besides sheer mass, low stiffness with sufficient mass and acoustic decoupling are very imortant for acoustic sound insulation. The relatively low stiffness of a straw-bale wall with earthen plasters is ideal. The fact that the cavity between the two plaster shells is filled with straw provides excellent acoustic damping. Beware and be careful to fill all cavities and voids with very light straw/clay. Avoid any direct mechanical contacts between the inner and outer plaster shells, as these will seriously degrade sound damping performance. Contrary to what you would expect, loosely packed bales will perform better than very tightly packed bales. Extra thick (>35mm) earth plaster specifically improves low-frequency performance. Cement and lime plasters perform almost as well but earth plaster with lots of straw is the best due to a lower modulas of elasticity (stiffness). Applying significantly asymmetrical plaster thicknesses helps to avoid coincident reverberation of the inner and outer plaster layers. The thicker plaster layer should be on the sound source side of the wall. Pay a lot of attention to all openings and edge details; these are the weak points. An air leak of only one sq. mm will seriously degrade performance. Door openings and windows are literally acoustic holes in the wall; these need special detailing and attention to even remotely approach the acoustical (and thermal) performance of the surrounding walls. Even double doors generally show poor performance compared to the wall. The gaskets and seals in the doors should be double or even triple, but even then there is a problem as, over time, the seals will degrade and leaks will occur. The type of door you are aiming for is more like a steel watertight door in a ship than a house door with multiple closing bolts and tightening clamps. (All of this only if acoustical performance is essential.)

table2In conclusion, I would like to emphasize that, due to the nature of a straw-bale wall (an excellent sound barrier), the wall is not the problem; the connections between the

wall and all other elements incorporated or surrounding it are. In other words, it is the same issue as with thermal and moisture performance. I strongly suspect that most sound isolation tests executed on straw-bale walls are measuring the defects of other structural components or mistakes in the test procedure (a non-calibrated sound source, background noise, and such).

Room Acoustics

Here are some simple rules of thumb depending on the type of acoustics you want, e.g., very lively to very well damped. Soft acoustic instruments require a “live” (reflective) room. Loud amplified sound needs a “dead” (absorbtive) room. The single most important parameter is the reverberation time and level. The harder the surfaces, the livelier the sound. A bathroom is lively, hence your strive to sing even if you can’t. The opposite is standing on top of a snow-bound hillock [small hill or mound] – virtually no sound reflects back to your view. The bigger and harder the room, the longer the reverberation time, e.g., a cathedral. Next the relative dimensions: an oblong box (like Concertgebouw Amsterdam) approaches the ideal. Preferably the relative dimensions are approximately 2 to 3 to 5; this ratio will avoid the formation of dominant harmonic resonance and standing waves. The exact ratios needed for a given acoustical requirement depend on the size and acoustic reflectivity. I personally prefer rooms without parallel surfaces, thus avoiding standing waves. I think if you finish a room with earth/clay plaster on straw-bale walls, with wooden flooring and a well-pitched ceiling, you will have quite acceptable acoustics for musical performances. If it’s too lively, you can always add some damping afterward by placing soft furnishings in the room or hanging curtains on the windows. A bigger audience also helps.

Good acoustic isolation is definitely one of good merits of straw-bale walls. It should be seriously considered for purposes where sound isolation is of importance. It would be hard to find a more affordable solution to building sound studios, quiet houses in noisy neighborhoods, or noisy workshops in residential surroundings.

<[email protected]>

Rene Dalmeier has been interested in straw-bale building since 1998. In June 2005, he finally took the plunge and turned his hobby into a profession by becoming a full-time straw-bale builder.

A whisper = 15 dB … Normal conversation = 60 dB. dB: Abbreviation for decibel(s). One tenth of the common logarithm of the ratio of relative powers, equal to 0.1 B (bel).

Sill Pan Design Detail – TLS #51

By Bales, Straw Bale Construction, Technical, Walls No Comments

 

Slope pan flashing to outside.

Slope pan flashing to outside.

Included in TLS #49 (Myths and Realities, Spring 2005) was a discussion of ways to deal with moisture at the bottom of windows. David Eisenberg shared a written design detail for a pan under the window to carry water away from rather than down the wall. We wanted to share a drawing of this detail and David kindly provided one for us to share in Tech Tips.

Here’s the portion of the discussion in which David details this design idea.

“Protecting the bales beneath the windows requires that you catch the water under the window and make sure it gets all the way out of the wall. In other words, ideally, you would have a pan of sorts under the window, sloped slightly to the outside, extending a bit beyond each side and with a lip at the back and on each end (so water can’t just run off the ends), and extending out beyond the exterior wall surface, with a drip edge – so that any water that leaks through or runs down the sides of the window ends up in this pan and is shown the exit. You can make these pans out of metal, plastic, ice and water shield, cast this shape into a concrete sill, anything that will keep the water from leaking through it, but the principal thing here is to make sure that the water can’t get into the wall below the window. You can put your window sill material, whatever it is, on top of this pan flashing being careful not to punch unsealed holes when you install the sill. It can take a little thought and ingenuity to do this, but it assures you that, when the windows leak, the water leaves the building.

sill2

Concept of pan flashing turned up at back and sides extending beyond exterior finished wall with drip edge. Extending behind finish or trim at each side of opening.

“That old practice of just putting roofing paper or plastic over the top of the bales and setting your windows on it and then plastering over it just leads the water down inside the plaster to the bales wherever the water protection ends unless it runs continuously down the wall under the window to below the bales (and we don’t recommend doing that).  It just temporarily moved the problem down, didn’t solve it.”

Planted Filter: A Modern Reed-bed System – TLS #58

By Technical, Wastewater, Water No Comments

This article originally appeared in TLS #58.

by Rene Kilian – Denmark

Save money on your black and grey water while protecting the environment!

Reeds and iris clean the wastewater in the planted filter.

Reeds and iris clean the wastewater in the planted filter.

All properties without sewage facilities in rural areas of Europe must meet minimum standards for wastewater treatment. It can be expensive joining on to the main sewage lines. A planted filter’ – a modern kind of reed-bed system with vertical waterflow – has low operating costs and is an inexpensive alternative.

Approximately 30 of these filters have been built in Denmark. The systems are planted with wetland plants, and occupy around 16m2 per dwelling.

The system complies with the latest Danish standards, which are stricter than the European standard.

Along with this, environmental impact is reduced and the homeowner can save money on sewage connection and payments.  The investment can be paid for through savings in less than five years, when compared to a standard sewage connection. Here is an example.

Reuse of treated wastewater
Søren Raffnsøe built his own straw-bale house, went about it in a way that was as environmentally and economically friendly as possible. The way that water comes in and out of the house has
been considered in a holistic manner, and is the first of its kind in Denmark.

The house has its own planted filter to treat wastewater. The system is only 8m2 because the house has a composting toilet.

The planted filter is a biological-cleaning system. The system, designed by René Kilian, is an effective alternative to a sewage connection. The system can even be integrated into a garden where it could resemble a garden bed growing with thatching reeds, iris and bullrushes.

Figure 1. A recycling system with the planted filter where water is reused in the washing machine and garden.                   1. Sedimentation Sedimentation tank for grey wastewater only. The source of the water may vary depending on local codes or regulations but might include water from bath, washing machine and kitchen. 2. Pump well with a level controlled pump. 3. Reed bed system or constructed wetland. 4. Tank for treated wastewater and treated rainwater. 5. “Green” pipe for reuse water to washing machine and garden. 6. Water vitalizer in drinking water pipe. 7. Fine filter for treatment of rainwater. 8. Untreated rainwater toward sand catcher and infiltration unit. 9. “Black”’wastewater from toilet to compost container. 10. Urine from toilet to urine container Design by Kilian Water Ltd., Denmark

Figure 1. A recycling system with the planted filter where water is reused in the washing machine and garden. 1. Sedimentation Sedimentation tank for grey wastewater only. The source of the water may vary depending on local codes or regulations but might include water from bath, washing machine and kitchen. 2. Pump well with a level controlled pump. 3. Reed bed system or constructed wetland. 4. Tank for treated wastewater and treated rainwater. 5. “Green” pipe for reuse water to washing machine and garden. 6. Water vitalizer in drinking water pipe. 7. Fine filter for treatment of rainwater. 8. Untreated rainwater toward sand catcher and infiltration unit. 9. “Black”’wastewater from toilet to compost container. 10. Urine from toilet to urine container Design by Kilian Water Ltd., Denmark

The recycled water becomes so clean that you can reuse it to flush the toilet, wash clothes and water the garden. As compost toilets don’t use water, Søren uses the water only in his washing machine and garden. See Figure 1.

Along with this, he saves 50 percent in his usage of drinking-quality water. To collect the excess recycled water, he has made a little pond in the garden, where there is an extra cleaning process that created a habitat for plants and animals. The drinking water itself is also special. He has installed a ’vitalizer’ in his drinking water pipes. This revitalizes the water so it attains the same quality as spring water.

Payback in less than five years

A planted filter of 16m2 suitable for a normal household, will cost around 60,000 Danish kroner/$11,083.80 USD. Connection to public sewage costs one household around 40,000 kroner/$7,389.21 USD. The investment can be paid back in less than five years, as you can save on annual wastewater bill payments. Ongoing costs for a planted filter are 0 kroner /m3; there is just a government tax of 1.60 kroner /m3. Costs for sewage are approximately 35 kroner /m3. This means a dífference of nearly 33.50 kroner / m3. With an average consumption of 170m3 per year, a household would save around 5,700 kroner/$1,052.96 USD per year, or 140,000 kroner/$25,862.20 USD after 25 years.

The planted filter at 8m2 in front of the newly built straw-bale house.

The planted filter at 8m2 in front of the newly built straw-bale house.

If you chose a reuse system in addition to this, and saved 50 percent on water consumption, you save 7,000 kroner/$1,293.11 USD per year. After 25 years, you will have saved 175,000 kroner /$32,327.80 USD. With the correct wastewater solution, you can really save money and protect the environment.

Sealing an Earth Floor – TLS # 55

By Floors, Technical One Comment

dirtThis is the second of a two-part article on creating a poured adobe or earth floor. See Earth Floor, TLS#52, for the first article describing how to prepare for and install a poured adobe floor.

By Tom Lander – New Mexico, USA

Now, weeks later after your floor is 100 percent dry, it’s time to seal and fill the floor with Linseed oil. Here in the South West our floors can dry in a matter of a few weeks but in humid climates error on the safe side.

Materials:

Linseed oil. We prefer raw linseed oil, less petroleum additives then the common boiled linseed oil but the boiled works if you are not concerned about petroleum out gassing. Even raw linseed oil has carcinogenic warning labels. Ask for an MSDS sheet. Linseed oil is made from flax seed.

Citrus Solvent (thinner) or mineral spirits, again petroleum out gassing

We are still learning how to estimate coverage and quantity so I’m not sure how much material is needed for your size floor. Maybe buy 2 gallons each for starters; you can buy linseed oil in 5-gallon lots.

Equipment:

4” paintbrushes, natural bristle is always best but pricey

Electric hot plate or gas camp stove

Large pot or kettle

Approved vapor mask

Safety glasses or goggles

Fan for air circulation/expelling fumes if you feel this is necessary

Rags,

Gloves

Prep floor:

Sweep or vacuum any loose debris and dust. You might want to do a light mopping or sponging. Give yourself time for the moisture to dry before applying the oil.

Procedure:

Heat the linseed oil to almost boiling (do not boil). We are just trying to heat the oil to aide in soaking, absorbing in. This must be done outside with caution, flammable. Another option is to pour the oil into a large deep baking pan, cover with a piece of glass and let it sit out in the sun. Leave an air gap. With either method start with a small batch to get the hang of heating and applying.

Transfer the oil into a suitable container. You can paint the material on or if you are quick, you can pour some onto the floor and swoosh it around with the brush. The only risk here is that you will not get an even distribution of material. Try it. Be consistent and watch how the floor is absorbing. If more than one person is applying, then you might get varying results but by the time you are done it shouldn’t matter. Use up your first small amount then decide how much more (a large batch) to heat for your next go at it. For reference keep track of how much material you use for each coat and offer this info to others.

The floor will soak up this first coat and there should not be any pooling of the oil on the surface. Plan your route of attack so you end up working yourself out the door, window or hallway. You should be able to go back to the start and do a second full strength coat right a way. Remember your shoes will be picking up dirt and dust from the outside so take steps to minimize this. There are disposable booties one can buy to cover their shoes.

What we are trying to do is seal the floor but think of it more like filling the floor. Filling all the little air voids between the sand and clay particles with oil.

The floor will dictate the timing and how much material. Watch how the material soaks in. You might be able to continue with more heated, thinned coats the same day, unless you are tired or sick from the fumes and not wearing a vapor mask.

Diluting:

The first two coats can be applied full strength. For the third and fourth coat combine 75% oil with 25% thinner, heat and apply. Watch the absorption, watch for pooling or puddling but also give the material some time to soak in; you just don’t want it to dry on the surface. Have a rag and thinner handy to wipe up any excess otherwise the material dries on the floor and becomes sticky. If this happens then it’s quite a job to use thinner and rags to clean the floor. Apply at least two coats of this first diluted mix.

Next is a 50% to 50% heated mix. Hopefully by now you have learned if pouring and brushing works for you (certainly faster) or just brushing or maybe it’s time now to just brush. Isn’t this fun learning as you go? Like all earthen materials, they tell you when and what to do, what’s the word? Experience.

Remember, oily rags and brushes are flammable so hang out to dry and do not leave a pile of rags unless it’s in the middle of a gravel driveway and you want to have some fun.

www.bioshieldpaint.com

Sunny Side http://www.gillroys.com

Where to Draw the Line – TLS #50

By Bales, Design, Technical No Comments

This article appeared in TLS #50.

by Chris Newton – Queensland, Australia

Can you design and build straw-bale homes for a hot and humid climate? Living in Queensland, Australia, I am frequently asked to identify an invisible line on the map where “she’ll be right” applies on one side of the line and “don’t go there” applies to the other. The part of me that fears litigation wants to respond with “ask me in 20 years time,” the technical part of me feels it has to be evidence based, and the logical part knows the answer already exists in the local environment. So I take on board here these three points and discuss how I attempt to find that line on the map in our building history, current research and the observation of the environment we live and build in.

Macro Climate

Queensland extends from 10 degrees south to 29 degrees south of the equator, covering more than 1.72 million square kilometres. Queensland is more than twice the size of Texas. Within Queensland, we live in monsoonal, tropical, subtropical, grassland and desert climate zones.

The table below represents summer (December though March) in the climate zones of Queensland. Summer is dominated by the monsoons making this a hot, wet and humid season. All zones in Queensland have mild and dry winters.

Microclimate

table3We can create a microclimate in and around our homes. Changes in air movement, moisture load or sunshine can significantly change the wetting and drying potential of a section of the building. When designing the house and gardens in a humid climate, we need to be aware of creating microclimates that cannot dry out.

Relative Humidity

Humidity is the water vapour held in the air. This is the ratio of the actual amount of water vapour in the air to the amount it could hold when saturated; it is expressed as a percentage. The capacity for air to carry water vapour increases as the air temperature increases. Air with a temperature of 30°C/86°F can hold more than three times as much water vapour as air at 10°C/50°F.

The dew-point temperature is temperature in which air must be cooled in order for dew to form. Droplets of water can be deposited within the straw-bale wall when air cools below the dew point and water vapour condenses.

Wood can absorb moisture content up to 25% from a relative humidity 98% (See Straube report in Resources at end of article). Straw is hygroscopic with its large surface area and internal pores having the ability to absorb moisture. A bale whose moisture content is at 8% will weigh less than the same bale with a moisture content of 20%.

 

Wetting Potential

graph

Table Daily Humidity in relation to Temperature Changes Source: Australian Bureau of Meteorology

We have a copy of an 1860 encyclopedia. It’s only damage is some yellowing and a few small brown spots (mold). This book had no special storage other than to sit on a bookshelf in subtropical Brisbane. So it seems that humidity alone may not be enough to cause decomposition of straw bales. However, I know through talking to people from Cairns that it is the norm to have molds growing on curtains, furniture and shoes throughout their summer. Newspapers and photos curl from the moisture they absorb. So humidity alone is enough to support mold growth in the tropics.

Historically, bathrooms have remained an area with high failure rates from moisture; this is true in any building type. Protection for straw-bale systems in wet environments exists. This can be in the form of vapour barriers, water barriers, design considerations, and attention to detail. It would be fair to say that, over the life of a building, some houses despite best efforts will experience elevated moisture levels in part of the wall system. Concentrated moisture only becomes a problem if the ability to dry is not timely for the given climate conditions. Remember that molds grow rapidly in hot and humid conditions, and are dormant in cold conditions.

Drying is the balance for wetting. The measure to ensure this includes a capillary layer below the bottom straw bale and a render with high permeability. Water vapour moves from low concentration to high concentration. High humidity will reduce the ability for the wall system to dry. In the tropics, rain may persist over several days. Attempting to dry clothes in the shade will take a long time during which they will acquire a moldy smell. You can not expect a wall system on the south side of the building to dry as efficiently as those on the north. High humidity will further compound this. (Note that we live in the southern hemisphere.)

Can you build with straw bales in a high humidity climate?

The line that removes high risk for straw-bale construction is unlikely to be a latitude line. Maybe it is a line that farmers have already identified. Grain farmers look for a climate dry enough so the grain dries adequately before harvest. The dry grain is then suitable for storage. Humidity is not a problem for the sugar cane growers who harvest the crop with high moisture content and send it straight to the mills where the juice is squeezed from the cane. So maybe the invisible line is found on an agricultural plan.

Resources

How Straw Decomposes, Matthew D. Summers, Sherry L. Blunk, Bruan M. Jenkins. www.ecobuildnetwork.org/pdfs/ How_Straw_Decomposes.pdf

Straw Bale House Moisture Research, CMHC (Canadian Mortgage and Housing Corporation). www.cmhc-schl.gc.ca/ publications/en/rh-pr/tech/00-103-E.htm

Moisture Properties of Plaster and Stucco in Strawbale Buildings, Dr. John Straube. www.ecobuildnetwork.org/pdfs/ Straube_Moisture_Tests.pdf

Monitoring the Hygrothermal Properties of a Straw Bale Wall, Dr. John Straube and Chris Schumacher. www.ecobuildnetwork.org/pdfs/Monitoring_Winery.pdf

Bureau of Meteorology–Australia. www.bom.gov.au/ weather/qld/

Chris Newton, Earth-n-Straw, Queensland, Australia, 0413 195 585, <[email protected]> www.newtonhouse.info. Chris, an owner/builder, educator and trainer in strawbale, plasters and other aspects of natural building, is the new President of AUSBALE, the Australia and New Zealand straw-bale building association.

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