Our office building project for the Trillium Lakelands Teachers’ Union features a straw bale wall system that combines conventional wood stud framing with an interior straw bale wall.
Recently, we finished the exterior side of this wall system. This involved placing dense-packed cellulose insulation in the frame wall, filling the cavity so the insulation is blown tightly against the straw bales. With the cavities insulated, we add approximately R-21.5 to the R-30 of the straw bales. Our contractor for the dense-packed cellulose was Morgan Fiene at New Energy Consulting in Hastings, Ontario (705-313-2004), whose care and concern for doing a thorough job was very refreshing.
We then covered the framing with an insulative wood fibre sheathing. This 1/2 inch wood fibre sheathing has an R-value of 4 per inch, and is made from 100% recycled wood fibre and a non-toxic binder. Made by Western Louisville Fiberboard in Quebec, this product is the cleanest sheathing product we could find. Most exterior wood fibre products use an asphalt emulsion coating, but the SONOclimat product uses a proprietary coating that is water based, non-offgassing and meets stringent environmental standards.
As a means to blend conventional wood framing with straw bale walls to achieve very high insulation values, we have been very pleased with the straw-cell system. It marries low impact materials throughout (earthen plaster, straw bales, cellulose insulation, FSC framing and recycled fibre board) with high insulation value and a straightforward construction process. It’s a great way to marry the more unconventional approaches to sustainable building with mainstream approaches.