There are several portions of Canada’s Greenest Home that do not have straw bale walls. While we believe strongly in the advantages of straw bale walls, we also want to show our students a more mainstream way to achieve high energy efficiency with low environmental impact: double stud framing and dense-packed cellulose insulation.
These sections of the building are framed with 2x4s and are the same depth (14 inches) as the bale wall cavities to give the house the same wall thickness everywhere. Since the dense-packed cellulose has a better R-value than the straw bales, these sections of the building will be very well insulated!
The cellulose insulation we used is made nearby in the Ottawa area from shredded, recycled newspaper and borax. It is a low embodied energy, local material with no real drawbacks environmentally.
Our first inclination was to use wet-sprayed cellulose, as we thought that this would be the best way to fill the cavities and prevent settling. However, the extra thickness of the cavities would have meant that the wet-sprayed cellulose would have had to be applied in several “coats”, adding time and cost to the installation. Our installer, Air Barrier Insulation, suggested dense packing as a better option.
A fine mesh is applied to the interior side of all the studs, which will let air out of the cavities but retain all the cellulose. The cellulose hose is then inserted through a slit in the mesh and the heavy blower (operating at about 60 psi) packs the cavity full of the insulation. The operator continues to pump the cellulose until the blower can no longer force any more into the cavity. At high densities (around 4 pounds per cubic foot) the insulation will not settle.
The dense pack blower machine is much more powerful than the typical rental units we’ve used to loose blow cellulose into attic spaces. Having seen this unit in operation, I’d definitely use this type of machine for retrofit applications as well in the future.
The application was quick, relatively tidy and surprisingly less dusty than anticipated. With such an excellent option available to any builder doing conventional stud framing, an affordable and environmentally friendly wall insulation option is an easy choice.