Straw is a wonderful building material for a number of reasons. It is, basically, a waste product. This is not the hay that is used for animal feed. Animals cannot digest straw. In actuality, straw is the stalk that comes from pretty much any grain. Once the grain itself has been harvested, the stalks are baled. It can be used for animal bedding. But a great percentage of straw is burned as waste. By putting it to use in building, less is burned, making it great environmentally. When it is baled, it is tightly compacted. This is useful because 1) it provides greater strength, 2) gives it a higher insulating value, 3) animals, such as rodents, find it difficult to nest in it, and 4) less open space for oxygen, making it more fire resistant. So now, let's break each of those down a bit.
Greater strength. There are primarily two ways to build with straw bales. One is using the bales in and of themselves, without any extra framework, and the other is by infilling a traditional type frame with the bales. As the bales can be used without additional framing, even for load-bearing walls, and in two story builds, this testifies to it's strength. The downside of this, is that it can make it a bit more difficult, although not impossible, to obtain building permits. While more and more places are expanding building codes to be inclusive of straw bale construction, many of those do require some sort of framework. This is one of those times when working closely with code officials will be necessary. Know your information well, as it may very well be a relatively unknown subject to code enforcement officers. But built correctly, it can easily last a hundred years or more. They have even been known to withstand earthquakes. They are tough buildings.
Higher insulating value. In any climate, building a structure with good insulation is imperative. Using standard insulation, anything with a rating of R=19 or higher is considered "super insulated". Tightly compacted straw bales average at about R=2.7 per inch. And as bales are generally between 16 and 18 inches thick, that would put the overall rating between R=43 and R=48 (according to this). As you can see, this is a superior insulating material. That being said, there is practically zero thermal mass, meaning it won't hold heat or cold for extended lengths of time. That is where a good natural plaster (such as cob or lime) come in. Adding a good thick layer will give the walls great thermal mass, as well as seal the wall for protection from insects, animals, and excess moisture. Moisture is the main thing that can be disastrous in a straw bale building. Proper sealing is absolutely required. And it must also be breathable. Modern wall sealants don't allow for this breathing. So if any moisture has been trapped inside, it won't be able to escape. Natural plasters are breathable and more forgiving as settling occurs over time. This prevents cracking in the walls that can, again, let in unwanted moisture. So why not include a healthy layer of a natural material that not only protects the bales, but also provides thermal mass?
Rodents find it hard to nest in. Ok, so it's not impossible for them to get in. But they don't like eating it, as they can't digest it. When the bales are tightly compacted, it's more difficult for them to get in. And with a good and proper plaster finish, it greatly reduces the odds of one of these critters getting in there. And the same goes for insects. While there may be some already in the straw as your building, once the plaster goes up, the ones in there cannot escape, and will eventually die. And new ones will not be able to get in. Now if you are utilizing a timber framework within which you will be placing the bales, you will have to do something for the possibilities of termites and any other critter that would find wood attractive. So that is something to keep in mind.
Fire resistant. This one almost seems like an oxymoron, doesn't it? Straw? Fire resistant? Actually, yes. Again, this comes from the fact that the straw is so tightly compacted into bales that there is little to no space for oxygen to flow. And without oxygen, fire cannot live. And, yet again, the final plaster further protects the straw in case something were to happen. In fact, tests have shown that properly constructed straw buildings are actually MORE fire resistant than traditional built homes.
Straw bale construction is easily learned, and can be done by the do-it-yourselfer. It goes surprisingly quickly. The bales, being the size they are, makes the walls go up very quickly. Bales can also be used as internal walls if you'd like. Just remember that that size will take up a bit of floor space, unless you have already planned for that and make the overall structure larger to accommodate that. Alternatively, one of the other natural building styles we've already discussed can be used for the interior.
Another great aspect of straw bales is that they are almost universally available locally. If you can become well acquainted with a local farmer, that helps a lot. You may, however, need to plan out in advance for the next year's harvest, to have the farmer set aside bales for you. If you do happen to be in an area where they aren't locally available, and you end up having to order them from elsewhere, that might factor into your plans in cost of shipping.
Now the downside is that while it is easy to build, and generally costs much less than a traditional build, especially if you're doing most of the work yourself, it is absolutely essential that those final layers are done properly. With straw bale, this cannot be stressed enough. Those finishes protect from water, rodents, insects, aid in fire resistance, add thermal mass, and are what essentially keeps the structure standing longer. If not done correctly, it can cause major issues down the road. It can be done by you. It is something that can be learned easily enough. With enough patience to make sure it's done correctly, this isn't a problem. But if you doubt your ability or patience, a professional may be necessary. This is where the cost can start to add up. Professionals in natural plasters don't generally come inexpensively. But with a good footing/stem wall, an adequate overhang, and solid plastering technique, I believe anyone can do it.
Straw bale homes may not be for everyone. But they are easily built, require readily available and renewable resources, provide excellent insulation, and as a bonus, absolutely incredible sound-proofing. Definitely consider this as an option. They can be built in just about any climate so long as proper precautions are taken for reasons of moisture and/or creatures that may try to claim the straw as their own. A flood zone may not be the best ideal, but otherwise, they are definitely worthy of consideration. For more information to begin your research, here are some valuable resources to check out.
https://www.strawbale.com/new-to-straw-bale/
http://buildingwithawareness.com/the-pros-and-cons-of-straw-bale-wall-construction-in-green-building/
http://pajaconstruction.com/advantages-and-challenges-of-straw-bale-construction/
http://www.greenhomebuilding.com/QandA/strawbale/varmints.htm
http://www.motherearthnews.com/green-homes/earthbag-cob-strawbale-zbcz1605
http://www.simple-living-today.com/straw-bale-house.html
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