The 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:
- 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.