Let’s Talk About Straw Bale Homes

About.com – by Marc Lallanilla

A house made of straw? Didn’t the big bad wolf blow that down?

The little piggy who made his house of straw didn’t fare too well, but Nebraska pioneers of the 1800s found that straw bale homes were an ideal shelter for the windswept prairies. Straw was — and is — as readily available throughout the Great Plains as it is worldwide, and many of those straw bale homes are still standing.  

Still standing? But how can straw bale homes be so durable?

In a word: plaster. The same material used on the exterior of stucco homes will easily cover a straw bale, and once it’s covered, straw is surprisingly sturdy and long-lasting. Insects don’t bother with it because it has no real food value, and once it’s bound into a tight straw bale, it’s surprisingly fire-resistant since no oxygen can get in. Canada’s National Research Council determined that straw bale walls can withstand temperatures up to 1,850 degrees Fahrenheit for two hours, making them safer than walls made of some other materials.

But are straw bales strong enough to hold up a roof?

Straw bales are strong enough to hold up a roof, but only on a one-story structure using a load-bearing technique named the “Nebraska” style of building after the homesteaders who pioneered it. Most builders now use wood framing to support the structure, and straw bales to construct non-load-bearing exterior walls.

What’s the advantage to straw bale homes? After all, wood is a renewable resource.

Aside from the environmental advantages to reusing what is essentially a waste product that usually just gets burned — creating an air pollution problem — straw is found universally, making it a local product that doesn’t need to get shipped long distances. But the single greatest advantage to straw is insulation: straw bales have a very high R-value, the resistance to heat transfer that measures insulation value. Depending on its thickness, a straw bale wall has a R-value from R-30 to R-45. By comparison, most exterior wood-framed walls have insulation with an R-value between R-15 and R-20. Because of their superior energy efficiency, straw bale houses can save up to 75 percent on heating and cooling costs each year.

That sounds great. But won’t my walls be as thick as a bale of straw?

Straw bale walls are thick, similar to the adobe walls found in buildings throughout the Southwest. There are two main sizes of straw bales, 18″ x 14″ x 36″ and 23″ x 16″ x 42″. Plaster will add a little more thickness, making your walls roughly 16″ to 19″ thick. Window and door openings are framed in wood and are usually curved inward, giving the openings a graceful, “old-world” look (see Images 2 and 3, above).

That “old-world” look sounds expensive.

On the contrary, straw bale construction is inexpensive, about the same cost as standard wood-frame-and-drywall construction. Bales of straw are really cheap, and the labor is so simple that a house’s walls can often go up in one day — some people have even had barn raising-style parties, which further reduces labor costs. But the real savings are in the occupancy period, when energy costs are slashed.

But I get allergic smelling hay.

Hay is for horses, and it’s usually a feed crop for livestock. Straw, on the other hand, is a completely different plant material that has no real food value — even to termites. In fact, straw is ideal for people with allergies because it contains no pollen, no formaldehyde or any other synthetic chemical compounds.

If strawbale homes are so great, how come they’re not everywhere?

Aside from people’s typical resistance to anything new (even though it’s hundreds of years old), straw bales sometimes face increased scrutiny from building permit agencies and bank finance officers. But many agencies, including the State of California, have now approved building codes that allow for straw bale construction because of its many advantages.

But there must be some disadvantages to straw bale homes.

Like many other building materials, straw bales don’t stand up to moisture very well. Because of this, straw bales are stacked on footings that raise them above any ground moisture. Plumbing is often placed in separate chase walls away from the straw. Additionally, roof overhangs are extended to prevent rain and snow from getting too close to plaster-covered straw bale walls. Despite this, many straw bale homes in New England and the Pacific Northwest — where they know a thing or two about snow and rain — have stood the test of time.

Sounds like people should really start shouting about their straw bale homes.

Yes, but they’ll have to shout from outside the house: because of its insulation value, straw bale houses are incredibly quiet — it’s often used in sound studios. In fact, many straw bale advocates tell the story of a Nebraska family who sat inside their straw bale house, happily playing cards while everyone else in town panicked — the family didn’t hear the tornado passing by outside.

http://greenliving.about.com/od/architecturedesign/a/Green-Building-Straw-Bale.htm?r=et