There are essentially two methods of constructing bale walls to support the roof structure and multi-storey walls (to a maximum of 3 storeys) in residential construction. They are:
- load bearing wall assemblies
- non-load bearing wall assemblies
Both systems have their advantages and challenges. We have chosen to focus our efforts on non-load bearing straw bale for a number of reasons. Moisture is the biggest enemy of straw bales during construction, and until a roof is constructed the bales are vulnerable to damage even when stuccoed. Load bearing bale walls must be compressed, leveled and stuccoed before second floor or roof assemblies are constructed.
Both non-load bearing and load bearing walls can be constructed on conventional basements with an engineered i-joist floor system, grade beams, reinforced slabs and rubble trench foundations. It is at this point the construction methodologies diverge.
Non-load bearing wall assemblies are a modified post and beam system, constructed from dimension lumber and plywood found at any local building supply center. These frame assemblies are the same width as the bales and become an integral and hidden part of the bales walls, buried behind the stucco along with the bales. They also form the ‘bucks’, the openings and structural members in which the windows and doors are inserted and secured. Once the box columns – the structural framing members that form the enclosures in which the bales will be stacked – are positioned, leveled and braced, a second floor or roof is constructed and the entire building is largely waterproof before any baling begins.
Tensioned stucco wire on the exterior provides a ‘form’ to bale to from the interior. The roof and its associated overhangs should be generous, not only ensuring protection for the baled walls but providing a dry and secure work area for bale storage during stacking, retieing, installing and tensioning stucco wire. It also provides a protected environment for stuccoing. The chances of bales getting soaked or newly applied cement-lime stucco being ruined by a summer thunderstorm or several days of rain is dramatically reduced or eliminated by completing the framing and roof first.
Battle Lake Design Group has been working on modified structural elements and techniques for straw bale construction since 2004 for our variable Western Canadian climates. We continue to refine and update the modified post and beam system in collaboration with Acius Structural Engineering Consulting to create additional labour and cost efficiencies for both builders and home owners building straw bale homes.
For more information on straw bale technology or our design services, feel free to contact us.