What is Straw Bale Building?
Straw bales were first used to construct homes by early settlers in the sandhills of Nebraska in the late 1800s. Faced with no trees to mill and soil too sandy to use for sod homes, they turned to the abundant supply of prairie grasses and their recently invented baling machines. Many of these turn-of-the-century homes, schools and churches are still standing.
Modern straw bale construction uses the same basic principles applied by the Nebraskan pioneers, but updated to meet current building code requirements. Straw bale homes offer insulation values of R-30- R-33. Environmentally, the use of straw bales replaces the majority of the framing lumber, manufactured insulation and plastic barriers with an annually renewable, agricultural waste product.
Straw bale homes consistently use less than one half of the heating and cooling energy required by standard frame homes.
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. Stud walls or timber frames can create the structure if you decide not to build load-bearing.
Load-bearing (or Nebraska) style bale buildings use the bale walls themselves to support the roof. Various systems have been used to "pre-compress" load-bearing bale walls to eliminate any "sponginess" from the bale walls and level them. A structural roof plate is placed on top of the walls, and the precompression system draws this roof plate down toward the foundation. The simplest and most effective system devised to date is a series of 9-gauge wires looped through the foundation and over the top plate, and tensioned using a come-along.
There are building code approved examples of both load-bearing and post and beam straw bale homes in Ontario. Many have received bank mortgages and regular home insurance. Much testing has been done on straw bale wall systems, and all tests to date show that they outperform the standard 2x6 frame wall. Fire tests show a burn time more than double that of a frame wall, and structural tests show similar advantages. The CMHC has been responsible for some of this testing, and they are generally supportive of straw bale building.
To date, most building inspectors have required either an architect's or engineer's approval of drawings for straw bale buildings before issuing permits. Reactions from building inspectors have ranged from enthusiastic support to strong skepticism and resistance. Until straw bale building becomes part of the Ontario Building Code, bale projects must be approved on a case-by-case basis.
Straw bale homes can be designed and built in any style an owner chooses, from small bungalow to two-story luxury. Many kinds of outbuildings have also been built from bales, from simple chicken coops to three-car garages and livestock barns. Bale buildings are most commonly finished with a cement plaster (or "stucco") on the exterior and a gypsum plaster on the interior, but any common interior or exterior finishes are practical to use.
Bales are a practical building material, abudantly available in most areas, and annually-renewable. It is worth considering using straw bales for your next building project if they are available locally.