Straw Bale Wall Test - ORNL FAQ

Q:Who uses straw?  
A:Millions have for many generations.

     These questions came directly from the students of Green Academy of Knoxville and Lyciem 51 in Kiev, Ukraine, and general public input on the Discussion Forum and Chat rooms.

Q:   I was thinking since you are trying to use straw as an insulator why can't you use hay. Aren't they the same thing? - Alexandria Rickerson
A:   Good question, and one that is asked pretty frequently. Hay and straw are not the same thing. Hay contains a lot more leafy material and seeds, and has much greater food value when used as animal feed. Straw, on the other hand, is the woody stems of the plants, what's left of the wheat (or rice or barley, etc.) plant after the "good stuff" has already been harvested. Though hay could be used - and in fact was used in at least one of the 100+ year old houses in Nebraska - there can be some problems with using it for construction. For one thing, the fact that hay does have food value increases the potential for insects, mice, and other such critters. For another, hay tends to compost more quickly (again, because of the nutrients in it), and can actually heat up and spontaneously catch fire. Not something you'd want to happen inside your walls! - Bill Christensen
A:   Hay is mown grass, generally used as feed for livestock. It therefore has a certain value to farmers or horse people. Straw is by-product of farming; it is grain stalks, waste material left after the grain has been harvested (thus you will hear of oat straw, barley straw, or wheat straw depending on the local crops). Straw is used as bedding for livestock, but is generally cheap, and available in quantity. Also, hay usually has a higher moisture level than straw due to differences in harvesting methods. Hay is also more prone to overheating when compressed. At a glance, hay is usually "green", while straw is usually "gold". some folk can tell city slickers 'cause they don't know hay from straw. - Alexandra Irvin
Q:   Why should anyone straw for insulation?
A:   Straw is inexpensive, renewable, long lasting if kept dry, and has good insulating value. - Paraphrased from February 25th video conference.
Q:   Why study the insulating value of straw?
A:   It has not been studied very much by scientist, but has been used for a very long time. - Paraphrased from February 25th video conference.
Q:   How much straw would it take to insulate a house?
A:   It varies from house to house. We used 40 bales for a wall 10 feet by 13 feet. - Paraphrased from February 25th video conference.
Q:   Did you have any problems building the test wall?
A:   It went well. It took 2 or 3 months to plan and 2 days to build. It was a typical construction project where you have to solve little problems when they arise. Sometimes you need a tool you forgot and have to improvise. We found the cement (stucco) a little harder to smooth than remembered we remembered. - Paraphrased from February 25th video conference.
Q:   Were there any other similar project in your country?
A:   One project was here 2 years ago an another in California about 4 o 6 months ago. They ended in lower results than anticipated and there were questions that came up that we resolved with this test. - Paraphrased from February 25th video conference.
Q:   Why did you begin this project?
A:   We started the project because the resistance to heat flow was unknown in a traditional straw bale wall system. - Paraphrased from February 25th video conference.
Q:   What about the durability of straw?
A:   This is best answered in the form of potential durability. Walls today are similar to walls built 100 years ago. At least a dozen or so are still standing. - Paraphrased from February 25th video conference.
Q:   Did you have any problems with water in your wall?
A:   Moisture is a concern. This experiment almost didn't take place. We purchased 50 bales but the moisture content was about 18%. On Monday, the day before we started to build, we went out to a farm and purchased more, dryer bales. It would have taken too long for the original bales to dry. For straw bale walls in general, a flood could be a problem. You would have to dry out the house. It could be hard to salvage. The wall systems would have to be opened up and dried. But, there is little or no experience in this matter. Decay starts when the straw reaches around 18-20% moisture content. Moisture content over time can also cause problems, so it is not just the catastrophic events that matter. - Paraphrased from February 25th video conference.
Q:   What about painting these walls?
A:   Since the straw bales are covered with a smoothed covering of stucco (cement) it can be done. The stucco can have a pigment added or it can be painted after it dries. You would like to have a paint with a higher permeability so you would not want an oil based paint. You want water vapor to get out so a water-based paint is preferable. - Paraphrased from February 25th video conference.
Q:   How about fire security?
A:   We have not tested fire safety issues at ORNL, but others have. We understand from the fire tests that they are actually better than wood frame walls that we use here (in the U.S.) with conventional insulati
on. - Paraphrased from February 25th video conference.

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