Straw Bale Walls
Green Building Systems
A year before we started building we found a farmer to grow our straw. Many people forget that in order to get enough bales to build a house it may be necessary to plan one or two years in advance if you want truly local straw. We found a farmer who was willing to promise us his entire crop of straw in advance. We also knew in advance that he would not grow enough straw for the entire house so we got about a third of our bales from his neighbor. Finally, at the end of our project, we heard about someone who was building with bales near us; they had not planned in advance so were getting a shipment of bales from Canada (about 4-5 hours away from us); we got some of the Canadian bales to insulate our attic that first winter. We are happy to say that about 98% of the straw in our house came from within 30 miles of our home; we watched it grow and watched it get cut and baled. What a rare treat it is to have known our house at every stage of its growth.
Our new building is made of straw from the same farmer as our first house. We love the fact that our houses are even more “related” by both being made from Bryan’s straw. Bryan Kolliakowski of Deerfield, MA. still farms, but now has to work as a driver for UPS. We wish that more people were building with straw, we wish Bryan had enough work farming so that he did not need to drive a truck for most of the day. We wish that all current building products could be replaced by locally grown, locally assembled materials. Perhaps that day is coming!
Before assembling the bale walls, we laid black locust boards on the stone foundation to create a moisture break. We chose black locust because it’s very hard and naturally rot resistant.
Next came the layers of bales. Bales were layered using a running bond (i.e. each bale straddles the two bales beneath it, the same pattern seen in brick structures). For stability, each bale was staked to the two bales below it using locally produced oak surveying stakes. Although the bale walls are not tied to the foundation, they are attached to the timber frame, which sits on the foundation. All bales near frame posts were tied to the posts by wrapping bale twine around the oak stakes, then wrapping the twine around screws that were screwed into the posts.
The new building uses a similar bale stacking method to the old building, although Andy Mueller, of Greenspace Collaborative, who did the bale and plaster work, had many improvements on our older method. Andy’s methods are site specific. What is best for one project may not be appropriate for the next. See Andy’s work at greenspacecollaborative.com.
Our bales were made from rye straw, which is a local, sustainably harvested spring crop. We used 2-string bales that weighed approximately 35—50 lbs. Theoretically, the dimensions of these bales were 36”x 18” x 14”. One of our biggest mistakes was assuming that all bales would be precisely these dimensions. Therefore, we designed the dimensions of the house not solely according to our needs, but according to the presumed bale size. Because the size of each bale varied somewhat, we ended up having to cut some bales anyway. Our advice: choose your house dimensions according to your needs. Bales are not uniform building blocks assembled in a factory; no matter what house dimensions you choose, inevitably you’ll have to cut some bales anyway.
In areas where straw bales could not be used (i.e. odd sized areas) we created enclosures using wood, burlap and/or hardware cloth and stuffed them with loose straw.
Once again, our new building uses essentially the same methods as our first house with some improvements designed to create tighter fitting bales and better insulated cavities of irregular shape. One of the products that we used more of in the new house than we would have liked is spray foam. This product which is commonly used to fill in the small areas around windows and doors; is very useful for some of the odd crevices that are hard to pack tightly with loose straw, so often a combination of loose straw and spray foam was used. We used a variety of “less toxic” or “environmentally friendly” spray foam products. Spray foam is not yet, but soon will be, made from completely natural and benign materials. We look forward to that day as spray foam has a variety of uses and can be found in great quantity on almost every building site.
|PROMOTING SUSTAINABLE DESIGN TECHNOLOGIES|
|VERMONT, USA info (at) earthsweethome.com|