The science of straw bale building

This article is excerpted from the August 2015 edition of the Fourth Pig newsletter "Force of Nature" - check out the newsletter and sign up here.

Even though straw bale building has been around for about 150 years, they are still fairly rare. That might be changing, in part because the research on straw bale has been increasing and the results are fantastic. 

Research in Canada isn't new, and the Ontario Natural Building Association has compiled some important studies. But it was the 10 year study in England at the University of Bath that has been turning heads recently. 

The researchers developed prefabricated straw bale walls (we reported on this in an earlier newsletter) that were " blasted by simulated hurricane-force wind loads, soaked in water to simulate flooding and exposed to roaring fires." They passed with flying colours. Because of their great performance developers and builders in England (like in Canada and the U.S), can now get permits and insurance.

And because straw is a renewable resource with a number of applicants it has tremendous potential to be an important approach to natural building. As one of the lead researchers at Bath said "Building with straw could be a critical point in our trajectory towards a low-carbon future.”

What's the deal in Canada? In Canada (and across the world) straw bale is used for residential, commercial and institutional buildings. Toronto’s High Park Community Kitchen building is straw bale, Mountain Equipment Co-op in Ottawa uses straw bale, Stanners Vineyard in Ontario, and Orifino Vineyards in BC have straw bale buildings. The U.S. Postal Service has started to use straw bale as insulation, a five-star lodge in South Africa is a straw bale building, and there is even a straw bale hotel in Switzerland. There are many straw bale homes in Ontario (including in Toronto, done by the Fourth Pig). 

What about Canadian fire codes? Test after test show that straw bale walls meet or exceed fire code safety standards. A conventional wall (wood frame/drywall) is designed to withstand temperatures of 760 degrees Celsius (1,400 F) for 30 minutes. The National Research Council of Canada did a test on a plastered bale wall and it withstood direct flames of 760 for two hours before a crack appeared. This rating is equivalent to cement (which means it can be used commercially). 

What about pests?
Straw has no nutritional value (unlike hay, which has seeds) and is therefore of little interest to rodents. In addition, rodents would have to eat through thick plaster to get to a dense wall that is not food. Straw bales are not carriers of insects, the density of the packs makes it very difficult to move. A conventional home is more likely to get a termite infestation than a straw bale home.
How sound proof is it?
Straw Bale walls provide a very low sound transmission, and varies in Sound Transmission Class from 50-70, which is significantly beyond the standard wall type with a ~40 STC rating.

Will it last?
Yes!  Straw bale walls are built to last. You need air and water for the straw to decompose and straw bale homes are highly resistant to moisture build-up. Lime and earth plasters have been used for centuries and last a very, very long time. A properly designed and maintained home with straw bale insulation will last and last. 

What are different ways that people use to build with straw?
We will let Chris Magwood answer that one: