In choosing a product to use at the core of our building assemblies, we researched all available insulation materials. We were looking for a product that was non-toxic, with no VOC’s, that would redistribute moisture that accumulated within the walls, that didn’t change properties over time, and that had excellent thermal resistance. We found all of this in 100% mineral borate treated, fiberized cellulose insulation. We have our own heavy-duty blowing equipment and have developed specialized methods to accommodate our thick assemblies. It works well installed at high densities in our walls, floors and Passive Roofs, and it works well blown loosely into attic spaces. We do most of our insulating in our shop, and bring our equipment to the job site to finish the project.
For supplemental insulation in the Service Cavities integral to the Structural Layer, which are filled after mechanical and electrical rough-in work is complete, we recommend and use one of two products. When the project is close to us and we are doing more than just the exterior shell, we generally use the same dense-packed cellulose that we use elsewhere in the project, blown behind a porous, gossamer fabric known as Insulweb. For other projects, we recommend either dense-packed cellulose installed by others, or mineral wool batts, such as Roxul Comfort Batts. With the majority of the insulation in the Blanket Layer, on the outside of the Airtight Layer, the service cavity insulation is well enough protected that nearly any insulation product will perform as advertised.
While we seek to minimize the use of plastic foam, it is arguably a better use for oil than burning it in energy-wasting cars or homes. We use the highest quality material with the lowest global warming potential, EPS (expanded polystyrene), in our Raft Slab foundation system, and also to insulate on the exterior of doors and windows, where the additional thermal protection is warranted. The product we use is the only rigid foam rated for termite resistance, using a natural borate additive.