How Straw Bale Houses Work
Straw Bale House Construction
Once you've decided whether to use a load-bearing or a post-and-beam structure, your design choices look a lot like those of conventional home building. A straw bale home can use any kind of foundation or roof, but many people try to consider features such as solar-paneled roofs, which enhance the environmental friendliness and the energy efficiency of a straw bale home.
However, with either type of straw bale house, the bales need to be raised off the ground several inches so that they don't soak up moisture from the ground. Builders can accomplish by using toe-ups -- platforms made of lumber and gravel that attach to the concrete foundation. Nails or pins should be hammered into the toe-up, and then the bales are placed onto the nails, anchoring the bales.
Once the first round of bales is situated on the toe-ups, then the rest of the straw can be stacked just like blocks. Window and doors are inserted into the straw bales with wooden frames. Cutting, notching and retying bales are all a part of this process. To get a bale the size or shape that you need, baling needles, which are like large sewing needles, are used to cut the bale and retie it with twine. Chain saws are used to make the notches that will fit the wooden posts.
After the bales are stacked, it's time to break out your chain saw again! Chain saws can carve out architectural features such as niches, window seats or heavier features such as cabinets. Upper cabinets are too heavy to be attached to the plaster that will cover the straw, so pieces of lumber with spikes are inserted into the straw. They will support the cabinets when they're installed. Electrical cables should be encased in plastic sheathing, but they can be installed directly into the walls. Plumbing, however, should be kept out of straw bale walls when possible by using internal walls.
When they're finished stacking, some straw bale builders use giant poles of steel or bamboo and slide them in from the top of the bale to keep everything in place, while others just use pins and wire mesh. Either way, plastering is next. Stucco cement, gypsum plasters, earthen plasters and lime typically serve as the internal and external plaster. The first coat of plaster should be worked into the straw, followed by two additional coats of plaster. Contrary to what you might think, you shouldn't use a waterproofing material on the walls. Straw will work moisture out by itself, and the plaster needs to ventilate the moisture, as opposed to holding it inside next to the bale. Wall paints also should be breathable; examples of breathable paints include lime paints, silicate paints and some latex paints. Properly applying the plaster and paint will help to ensure that moisture doesn't affect the straw.
We'll take a further look at the threat of moisture on the next page.