Because we got stuck...
Or rather, I (Katie) got stuck. There has been lots of progress in the realm of passive house building, which is great for ensuring that the energy and therefore carbon use during operation is low, but a number of the common materials in the wall assembly - foams, wraps, plastics, resins, and generally carbon-intensive and non-natural materials - left me dismayed. So although we had started getting contractor quotes in December 2018, I needed to hit the pause button and do some research.
Straw bale - a natural building block
Straw bale wall assembly.
Fine Home Building. https://www.finehomebuilding.com/2018/10/10/houses-design-case-straw-bale-houses
As I investigated a number of insulation and wall types, I came across straw bale building, which is a hybrid system of straw bales and plaster. Running bale walls are covered with some sort of plaster (clay, lime, etc.). There are two basic types of straw bale buildings - load-bearing and non load-bearing. The non load-bearing walls allow you to build above one story by using a wooden structure, such as post and beam like shown on the right above.*
*https://www.mdpi.com/2071-1050/11/12/3388/htm#B47-sustainability-11-03388
*https://www.mdpi.com/2071-1050/11/12/3388/htm#B47-sustainability-11-03388
History
Pilgrim Holiness Church (Arthur, Nebraska) built with strawbales in 1928 is still standing in good condition.
By Ammodramus - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=11054846 |
"The horse-driven baling machine, invented and introduced into the grain-growing regions of the North American West in the 1870s, had the unintentional side effect of turning mounds of loose straw into tight, easy-t-handle building blocks. The settlers of the Nebraskan sandhills, who faced a lack of lumber and suitable sod for building their new homes, were the first to put these building blocks to use. Some of these early bale structures are still standing and occupied – a testament to the durability of straw bale walls and the community spirit.” - More Straw Bale Building by Chirs Magwood, Peter Mack, and Tina Therrien
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A Strawhouse - Won't the Big Bad Wolf Blow it Down?
Today's straw bale buildings are not like the one of The 3 Little Pigs fame. Wind, rot, fire, critters - straw bale systems perform well when built well. For details, check out this FAQ from Andrew Morrison, head of www.StrawBale.com, major contributor to the straw bale section of international building code, and experienced builder of 100s of straw bale homes around the world.
Research Results
I got lots of great books from the library and from Magers and Quinn bookstore and read lots of websites. We also talked to an architect locally, who has been involved in projects in MN and WI, had a conference call with Chris Magwood from the Endeavor Centre, an industry pioneer in Ontario, and talked with a builder in Colorado (strawbaleconstruction.com). These three alone have been part of hundreds of straw bale projects in a variety of climates (including cold, snowy ones like that of MN) and legal jurisdictions (rural and urban). The more I dug into this construction type, I began to see many upsides:
* California Straw Bale Association. (2019). Straw bale building details: an illustrated guide for design and construction. New Society Publishers. Gabriola Island, British Columbia.
**Chris Magwood, Peter Mack, and Tina Therrien. (2005). More Straw Bale Building. New Society Publishers. Gabriola Island, British Columbia.
*** https://www.epa.gov/energy/greenhouse-gas-equivalencies-calculator
- Good insulation and thermal mass- an 18" thick, 2-string wall has an R-value of 25-30 and therefore resists change to temperature.
- By-product reuse - straw is an agricultural by-product from the harvesting of grains such as wheat, oats, rye, etc.
- Low embodied energy - as a quick-growing, agricultural by-product, it takes relatively low energy to produce a straw bale building block (straw bale: 0.24 MJ/kg; for comparison - EPS foam: 117 MJ/kg and fiberglas: 30.3 MJ/kg)*
- Fire resistance - lab tests give straw bale walls a 2 hour fire rating, which is greater than the 20 minute rating of much current standard construction. There are multiple instances where straw bale buildings have even survived the infamous wildfires in California of 2017!
- Non-toxic materials - no off-gassing risk from these walls.
- Carbon sequestration - a straw bale sequesters approximately 26 lbs of CO2.** This means our home will sequester approximately 18,000 lbs of CO2, which is the equivalent of driving a car 20,000 miles or the amount of carbon sequestered in 10 acres of forest in a year.***
- Sound privacy - the thick walls significantly dampen sound.
- Code compliant - the first approved straw bale home in Minnesota was built in 1997, and the International Residential Code now officially recognizes the building type with Appendix S: Strawbale Construction with Commentary.
- Community building - the concept of straw bale building is just fun. It is fundamentally a simple building process, and it is a blast to work collectively as part of a "barn raising."
* California Straw Bale Association. (2019). Straw bale building details: an illustrated guide for design and construction. New Society Publishers. Gabriola Island, British Columbia.
**Chris Magwood, Peter Mack, and Tina Therrien. (2005). More Straw Bale Building. New Society Publishers. Gabriola Island, British Columbia.
*** https://www.epa.gov/energy/greenhouse-gas-equivalencies-calculator
Straw bale building was looking pretty promising, but I needed to check it out myself. That's when I went to a week-long workshop build in Kingston, WA in Sept. 2019 put on by straw bale expert, Andrew Morrison (www.strawbale.com), who has built and consulted on hundreds of projects. Our host, Kathy, was building a house, and 35 people from across the US, came to help her and learn the process. By the end of this experience, I felt assured that this would be a viable option for our house.
