STRAW BALE BUILDING

Straw is the dry stalks of harvested wheat, barley and other cereal plants. Tightly baled and used for exterior walls, straw is a strong, non-toxic building material with great durability. As with any straw bale construction, Tenax, a plastic mesh, keeps the straw in place and provides a base for the cement plaster that covers the interior and exterior.

A breathable, silicate-based paint covers interior and exterior walls, allowing moisture to pass from the house through the straw and ensuring the bales stay dry -- no vapour barrier is necessary in straw bale construction. It's hard to beat straw bales' insulating value, which proponents claim has an R value of 35 to 50, double to triple that of a conventional wall.

Any type of straw can be used, including wheat, oats, barley, rye and rice. Bales used for building are not custom-baled, but must be dry (less than 20% moisture) and tight. Two string bales are the Canadian straw bale construction standard, but in places where larger, three-string bales are the norm they too can be used and offer insulation values of R-55.

Straw bale buildings use the same foundation, flooring and roofing technologies familiar to builders of frame homes. Basements, slabs and pier foundations can all be easily adapted to straw bale construction. Similarly, prefabricated trusses can be used to provide the roof structure.

The straw bales in the walls are stacked in a manner similar to bricks or concrete blocks, in running bond. Window and door openings are created using wide, rough frame wooden bucks inserted into the walls during construction. The first course of bales is always started on a 2x4 curb, to lift the bales higher than the interior floor level, in case of flooding or spills.

There are two basic styles of straw bale construction. Post and beam style uses a structural framework to support roof loads, and the bales are either wrapped outside the framework or in filled between the framing members. While wooden post and beam systems are the most common, concrete and steel frames would also be suitable. Straw bales are a practical building material, abundantly available in most areas, and annually-renewable.


-chris c. --