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We are in the middle of building a straw bale insulated home. I often meet people who assume I am therefore some sort of straw bale evangelist. This always strikes me as odd because I can’t really understand why I would want to push my building choices on someone else. As an adult, I feel perfectly able to consider the options and weigh which ones fit our desires and needs. Therefore, I feel most adults are likewise capable of the same.
So, if you have to ask why you would build a straw bale home, please don’t build one! If you think straw bale homes mean rodents, rotting straw, fire or other similar disasters, please insulate with something that you are comfortable with. Rest assured that we don’t care and certainly won’t judge your choice harshly!
That said, if you are interested in straw bale, let’s consider why you might do it
Some people are extremely sensitive to chemicals that are often used in common building materials. Think of the glues in plywood or OSB. These are often harmful whether you are sensitive or not. Think of some of the flame retardants used in things like insulation. If you choose the right bales, you can be assured that at least those aren’t introducing more chemical outgassing into your dwelling.
Straw bales provide an insulation value of somewhere between R40 and R50, depending on the bales and installation. This would be an expensive level to reach with typical pink fiberglass insulation.
Straw bales are relatively easy to install, leading to a good opportunity to do it yourself. Keep in mind that it is very labor intensive though, so if you don’t have help or lots of time, it could end up being the wrong choice.
Straw bales properly installed in a coating of plaster have been shown to be extremely fire resistant. In fact, in lab testing, it was found to be far superior to standard wood frame construction.
Straw bales turn out to be relatively pest resistant, owing to two details of a typical installation. First, both sides are covered in wire and plaster, making a solid surface (actually 1+ inches of rock in the case of lime plaster) that prevents entry of any rodents. Second, the bales are installed very, very tightly. This leads to very little space within the wall for a rodent to even move about. In fact, the stud cavities in traditional wood-frame construction leaves much more open space for a rodent.
This isn’t something that you often hear discussed, but consider the energy used in creating the pink fiberglass insulation in a typical wall. It requires quite a bit of energy to make, package, and transport such a product. Compare that to straw that is typically locally sourced and is grown using solar energy. There is the energy used for planting, harvesting, etc, but it is still much lower than the typical insulation product at a building center.
Mold is a topic that often comes up with straw building discussions. Yes, if the wall cavity is continually kept damp, mold will be present. However, this isn’t unique to straw building by any means. Consider what moisture in a normal wood-framed wall does. It isn’t pleasant either. So, yes, mold is absolutely an issue, but that is true of any building form. Just be sure to consider flashing, overhangs, and plaster types and thicknesses. All these things work together to prevent mold/moisture issues.
Big Bad Wolf
This just has to be addressed because it is almost always the first response when people hear about a straw bale project. Apparently the three little pigs story has really ruined straw’s image as a building material! There are numerous techniques for building straw buildings, so all can’t be covered here. Instead, let’s address the form we have chosen for our project. First, the actual support comes from good old wood. We use a form of post and beam framing, which provides larger openings than standard stud framing to stuff the straw into. So, even without the straw, the building is structurally sound. Second, the bales are pressure fit into the walls, making them quite secure. Third, the bales are then covered with welded wire, tying everything together and providing good sheer strength. At this point, there really is no great worry of “blowing the house down”. Finally, three coats of plaster are applied inside and out. We have chosen lime plaster, so the end result is over 1 inch of limestone coating over the bales. Suddenly, wood framing and vinyl siding is sounding rather inadequate.
All that said, straw bale building is no panacea. It has drawbacks just like any other system.
The walls take a lot of space as a typical bale is 18″ wide. That level of insulation takes space! Keep that in mind when designing rooms.
Straw bales take a lot of labor to handle. They are bulky and need to be stacked and stacked again during the process. Installing them means notching and re-tying. Plastering is hard work and usually 3 coats are required.
Straw bales are messy to work with. When they are handled, they leave a big mess. When they are notched and re-tied, they leave a bigger mess still.
Straw bale construction is not very common, so finding skilled labor to help is unlikely. There is plenty of education available online and in books and videos, but it requires time to learn. Please do consume such material though as there are a few mistakes that can be made that could turn a project bad.
So, don’t look to me to push straw bale building on you. You need to choose what fits your needs. If you choose conventional wood framing and are content with that, wonderful! If you want something more unusual, great. Look at all the options — straw, cord wood, cob, etc. Above all, have fun and build something beautiful that makes you happy! Happy building!