Why Straw Bale?
Straw bale building technology has been around in wider use for a few decades, but has only started to enter mainstream consciousness in the last few years. It is an accepted building method, having mainstream appeal and professional acceptance amongst owners, builders, engineers, designers, architects, and CMHC*. There are standardized straw bale building codes in many US states.
Unlike other ‘new’ building systems, straw bale technology does not come from within the construction industry. Straw bale has appealed as a sustainable solution because of a grassroots desire to build more efficiently and effectively.
The technology has hit a nerve in our collective thinking as we redefine and reassess the concept of housing, sustainable building systems, and energy efficiency.
*Straw Bale: A Selective Biography, Canadian Mortgage and Housing Company
The Western Canadian Climate
Our climate posses many challenges to creating energy-efficient, long-lasting straw bale buildings. Battle Lake Design Group, Inc. has worked extensively with Habib John Gonzalez of Sustainable Works, Ltd of Nelson, B.C. since 2004 to fine tune straw bale construction for Alberta’s harsh and variable environment. Habib is considered on of the foremost experts on straw bale construction in Western Canada, and is a contract researcher for CMHC. Simplicity of construction, integration with standard foundation, framing methods, design, and assembly that provide superior protection from weather and moisture during the construction phase and for the completed building have been the areas of our focus. This has resulted in a high level of acceptance and approval within most jurisdictions and with building inspectors.
We have also developed a collaborative partnership with Acius Structural Engineering of Edmonton, Alberta, that not only provides engineering for our designs as required but is proactive in the promotion of straw bale buildings.
Reasons to Use Straw Bales
- Local and readily available material
- High level of energy efficiency – high R-values (RSI) and elimination of thermal bridging
- Cost comparable to conventional frame construction
- Design benefits – easily adaptable to a variety of design styles, from traditional to modern.
- Allows for the creation of curved walls and organic shaped surfaces
- Low tech/human scale – lends itself to community based participation, with good results for people with entry level building skills
- Quiet – excellent sound barrier with pleasing interior acoustical properties
- Strength – twice the load bearing capacity of a typical 2×6 wall
- Fireproof – 2.5 hour fire rating
- Healthy indoor environments and air quality – there is no vapour barrier, as a result indoor air quality is better than in ‘conventional’ structures
- Significant environmental benefits
- Reduction of energy to heat and cool
- Annual renewability of the resource
- Low embodied energy
- Product is not, and cannot be, patented or become proprietary
- Possesses high stability under seismic stress
Overview of Straw Bale Building Techniques
Straw bale buildings can be divided into two main categories:
- Load bearing
- Non load bearing
Load bearing buildings have a ‘top plate’ or box beam on top of a compressed straw bale wall. The roof or second storey is supported on this plate.
Non load bearing buildings depend on a post and beam or ‘light frame’ construction for structural support and the straw bales are an infill or ‘wrap’ around the structure.
Our preference is for non-load bearing straw bale buildings. They allow for the construction of the frame and roof before installing the straw bales which eliminate one of the biggest threats to the baling process – moisture.
Our straw bale design is adapted to conventional basement and joist flooring systems. Alternative foundations such as at-grade rubble trench and stem wall system or modified strip footing can be used. Essential details of any straw bale foundations include toe-ups and associated flashing and insulation for moisture control.
Bales are laid in a running bond pattern between box columns with a top plate or beam and stucco wire on both sides sewn through the bales on each bale course. A scratch coat and colored finish coat of cement/lime stucco is applied on both sides forming a fireproof, structural skin panel.
Second floors and roofs
Floor systems are usually conventional dimension lumber or I-joists with walls and roofs conventional frame construction. Straw bale can be used for second floor walls but does not adapt well to gable ends and angles under roofs. If second floor is frame stud construction, it is recommended the framing be wrapped on the exterior with rigid foam insulation to reduce associated thermal bridging and increase R-values.
Doors and Window
Doors and windows are contained in framed bucks. The extra thickness of the walls allows for deep window wells, seats or alcoves around these openings and become significant interior design elements.
Interiors & Finishing
Interior walls are usually conventional frame walls and can be finished with drywall, wood or any suitable material. Cupboards are mounted or hung from horizontal wood ledgers or girts that are bolted through the straw bales before the stucco is applied. Electrical wiring is run between the bale courses before the stucco wire is applied. Most electrical boxes and wiring are attached to framing members and box columns if possible.
Applications Where Straw bale is Not Suitable
Straw bales are not suitable for below grade installation or any location where they would be exposed to excessive amounts of moisture and water. Generous roof overhangs need to be designed into all straw bale buildings to provide protection from the elements.
Why Straw Bale? A Summary
Straw bale construction is a visible part of the interest in the revival of ‘natural building’. These buildings are, in part, constructed of minimally processed, renewable material that is readily at hand in Alberta. The vapour-permeable cement-lime stucco provides a passive alternative to enclosed ‘plastic-wrapped’ indoor environments and associated VOC’s, toxins and poor indoor air quality.
Straw bale buildings can be more spontaneous, free form, organic and connected. They may best not be described as low tech, but as appropriate technology. As we in Alberta become aware of our need to reduce our ‘footprint’ on the planet, straw bale building can be part of the solution.
CMHC Research on Straw Bale Housing – Canadian Mortgage and Housing Corporation
Strawbale Construction Code Supporting Documentation – Ecobuilding Network
Building Science for Straw Bale Buildings – Building Science Information