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Building an Energy Efficient Straw Bale Home: Design criteria for Inglewood straw bale

By Bales, Design, Issue 70, Straw Bale Construction No Comments

This article first appeared in The Owner Builder 196 August/September 2016.  www.theownerbuilder.com.au

By Brian Hodge

As we embark on our 20th owner-built home, I reflect back over the progress since purchasing property last year.

We were surprised the property didn’t have power, sewer, or water but discovered it actually had sewer connection just over the back fence. We were somewhat pleased when we received the quote for electricity connection of $5,050. Mind you, that did not include the connection of the power to our meter box.

Having mentioned the meter box, I am flooded with the memory of its incorrect positioning in my unavoidable absence and the challenges that we were faced with as a consequence (see TOB 195 June/July 2016). But who can complain. The end result was that we have revisited the design and now have a better one that is more interesting.  And who can forget the bonus sewer connection at the back of the block, which will save us around $10,000 that we would have spent for a septic system.

A place to run courses

When we first went looking for land our primary motivation was to get a low cost piece of land on which we could run the practical part of our owner-builder straw bale building workshops. This was a precursor to being willing to sell the straw bale house in Ladys Pass. To be a straw bale building consultant with nowhere to do courses and nothing to show people was not an option and the solution had to make financial sense.

Consequently, I did an internet search for ‘land under $50,000 Victoria.’ The result was land in Loch Sport, which was too small and, from previous experience, has too many mosquitoes, and land in Inglewood, Victoria. Inglewood is in central Victoria about 35 minutes north of Bendigo with a population of a bit over 1,000. It was established in 1859 and is still a great place to find gold. It has a good supermarket, hospital, permanent doctor, pharmacy and most important, a couple of good old fashioned pubs for great meals. It is also the town where my youngest son, his wife and two of my grandchildren are located. However, the criteria were primarily price and size.

There was an 8000m2 block for around $45,000 near a light industrial area, a 2000m2 for $70,000 or a 1000m2 for $35,000. We put in an offer of $33,000 on the last block, which was accepted.

Position, position…

The only issue, which was a big one, was its orientation. It is only 20 metres wide and faces north-west. In order to control heat input and get some passive solar benefit in the design, we had to design a house that is twisted on the property. This option consumes a lot of land, which was complicated by our need for wide eaves for a straw bale house. Regulations stipulate that living area windows must have a minimum of 1000mm of clear sky from the boundary, which meant that we had to be set in from the side boundary a minimum of 1900mm to allow for the 900mm eaves. We also needed truck access to the backyard to take deliveries of bales etc. for workshops, further restricting our build space.

We finally settled on the concept of building a U shaped house with a central courtyard as this would enable us to get passive solar benefit in the master bedroom and living area. Not a huge amount, but enough to make a difference. It also provided us with a outdoor private area, which is important to us as we have lived on country properties for the past 12 years.

U-shaped floor plan

U-shaped floor plan

Energy rating

I had our energy assessors check to see what difference this adjusted orientation would make on stage one of the construction, as opposed to building parallel to the front boundary. We were surprised that the energy rating actually went up from 5.4 stars to 6.3 stars even though there is only one window that faces north.

As we are building in central Victoria, the energy rating is primarily directed toward the energy required for winter heating. However, we get some really nasty weather in summer with temperatures reaching high 30s and even mid 40s. Consequently the design criteria also included resistance to summer heat. The central courtyard faces due west, however it has a deep verandah to protect smallish windows from the afternoon heat from the west, and the windows facing east are limited.

One of the big concerns for restricting heat input in summer is to avoid doors that open directly into the house from the north, as it is the north wind that brings high temperatures to the area. I have therefore included a good size entry on the northern end of the house with the external door facing east, which will dramatically reduce the impact of those hot northerly winds.

Airflow manipulation

The cooler summer breezes often come from the south-east, so we have included casement windows on the south-eastern boundary to funnel those cool breezes through the house. The benefit of correctly hinged casement windows is that they tend to trap the breeze and funnel it into the house rather than simply working with straight airflow. When you are trying to get cool air into your home it is best to open the windward windows fully but close the windows on the opposite side of the house to 50%, as this creates a vacuum resulting in greater airflow.

As this is a residential block I expect that airflow will be a bit of a challenge as we have boundary fences which will restrict it. I have also incorporated a flat ceiling in part of the house in order to accommodate ducting for an air circulation pump to force the early morning cool air through the house if the temperature in the house is higher than the temperature outside. Our previous straw bale house in Ladys Pass had the same issue, which was overcome using an evaporative cooler as an air circulation pump. The cooling function of the unit was hardly ever used, and would not have been missed, so I am planning on simply fitting an air pump this time.

The master bedroom window faces north onto the central courtyard, however the window is not within the shadow of the verandah roof so we will get good passive solar benefit in winter. It also means that we have a private outlook, and with Molly, our big guard dog, we are assured of security! (Molly is a miniature Maltese Shiatsu)

As this is house number 20 for us personally, it was difficult to find something a bit different to do, so we eventually settled on a curved roof with a curved ceiling. This will be achieved by building box trusses on site. It is a very cost effective method of roof construction and I am looking forward to trying it out, as I have never done it before.

With all the design, engineering and building permit issues behind us it is now time to get to work and build it. I am going to take my time and enjoy the process as I suspect this will be the last home that I build, although many people scoff at this idea, thinking that I am either crazy for building so many or that I am addicted to the process. Personally I am not sure, but I am going to enjoy this project as if it is my last.

Brian Hodge is the director of Anvill Straw Bale Building Consultants. He has nearly 40 years experience in the building trade, and now consults predominantly on straw bale construction. Brian is the author of ‘Building your straw bale home’ and will be blogging about his build. Anvill Straw Bale Building Consultants: Whether you are building a mansion or to a strict budget, we are here to help.  www.straw-bale-houses.com

Framing Bale Walls: How to

By Bales, Issue 63, Straw Bale Construction, Technical, Walls One Comment

By Andrew Morrison of strawbale.com

Image 1There are many different approaches to framing a straw bale house; however, there is one in particular that I have used on the vast majority of my projects over the years. It is a post and beam frame system with roots in conventional framing techniques. Because I came to straw bale construction many years ago as a general contractor practicing conventional construction, I brought some of that detailing over. I should preface this article by saying that there are right ways of framing and wrong ways of framing. The system I describe in this article lands in the “right way” column, but so do many other styles. As long as you are working with a structurally sound and safe system that brings you the best results possible for your style of building, then go for it.

Image 2One of the first details that often surprises people is the spacing of the posts in the system I use. I hear people talk about wanting to reduce the amount of notching in the bales by spreading their posts out as far as possible. I disagree with this approach and instead keep my posts relatively close together: no more than 6’ apart. One reason for this is that when the bales are stacked in between posts that are set far apart, there is no point of attachment for the bales other than the top and bottom of the wall. As such, the wall becomes weak as it is stacked higher. When posts are set closer together, the notches at each location provide a point of connection to the frame and make the wall much stronger both during construction and for the life of the structure.

Image 3One way I keep the posts close together is by incorporating them into the window and door frames. By using 4×4 posts as the king studs I end up with wider nailing surfaces on either side of the opening. This allows me to attach the finish trim, plaster channel and/or plaster lath, and welded wire mesh around every opening with positive attachment to the frame. These king studs serve two purposes by providing the nailing surface and by acting as part of the overall structural frame. Because windows and doors are placed in many locations around the home, and because I otherwise limit my post spacing to no more than 6’, I can minimize the wall beam size as a result. This minimal wall beam is important because the bigger the beam, the more expensive it will be. Further, larger beams are made from larger trees (unless an engineered beam is used) and I want to reduce the size of the trees I am using in my projects for environmental reasons.

Okay, let’s take a look at how the system works and why it can save time and money in your building process. I’ll simply lay out the process so you can see, step-by-step, how it comes together.

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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.

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.

Welcome!

By Uncategorized No Comments

Important!
We have identified and fixed a glitch in our subscription system that created problems for non-U.S. folks to subscribe.  If you have had problems in the past, please try again and let us know if you continue to have problems.  Thanks for the support!

The Last Straw has undergone a transition over the past year and we’re having a revival of our own.

Russian_BalerWe are now part of the Colorado Straw Bale Association (COSBA).

TLS has come a long way since the days of Out on Bale (un)Ltd where it was created back in 1993.  It is with great honor that we continue the TLS tradition and have the opportunity to upgrade it to reflect the times in which we live.

While much has changed behind the scenes our mission remains the same, which “…is to inform and inspire people to build more consciously and with foresight toward future generations.

With the digital age well upon us we are offering our subscriptions a little differently and hope to bring you even more interactivity with the publication.  By becoming an annual subscriber you will receive both print and pdf versions of each issue.  We want you to be able to access your documents from wherever you are, which means we are considering implementing an online reader for your convenience.

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