Having built out of bricks, and out of wood, I am now completing my Three Little Pigs story by building out of straw. I was lucky to meet Nicole, who is building her own straw bale house in a small village in Switzerland. See her blog here: http://www.lamaisonenpaille.blogspot.ch/
When baled, straw behaves partly like a substance, partly like a module. It is dense enough to require a saw to cut it, and it holds its shape when notched or sliced. (Of course, the bales need a certain thickness and density for this to work.) And yet, bales can be reshaped by shifting the straw around inside the strings. They can be taken apart and reconstituted (although we try to avoid that because they are always less dense than the first time) They can be compressed.
Bales are directional, with all of the stalks running parallel. At first, Nicole wanted to build her walls with the stalks running parallel to the wall, but she switched to perpendicular. With the stalks running parallel, the bales have a better insulation value because heat is not conducted as easily from inside to outside, but the smooth stalks do not take rendering as easily. With the stalks running perpendicular, bristling out from the wall, she can use a hedge trimmer to even out the sides before rendering, and the render holds well.
We use the bales to infill the space between wooden studs. Nicole purposely asked her carpenters to make the spacing between the studs uneven, sometimes at 90cm, sometimes at 95, sometimes at 100. This means she can accommodate the imprecise bale sizes. Our first stop before the day's work was at a nearby farm to inspect some bales that she might buy. I watched as she went through her criteria. Are they approximately the right size? Are the fibres long and continuous from one side of the bale to the other? Are there only stalks, or are there some residual grains that might attract rodents? Are the strings tight enough? Are they dense enough? She weighed them with a bathroom scale. They need to be at least 15kg for a bale 43x47x95cm.
To insert a bale, we often use pieces of sheet metal on the sides to ease the friction between it and its neighbours, and to ensure that all of the stalks slide past the wooden structure. This is a system that Nicole came up with herself. There is a big wooden mallet called the Persuader that helps a stubborn bale fit into place as well. Once in the wall, we add extra compression by standing on the bale and then screwing a wood slat into place on top of it.
|The mallet has a name. It is called the Persuader. (picture taken by Nicole)|
|These metal sheets are an ingenious idea of Nicole's- they ease the friction on the bale and make it easier to 'persuade'.|