Green Building Library
Project Showcase
Insulation and Air Sealing
Caulk, sealants and insulation were selected for their low concentrations of volatile organic compounds.
Spray-foam insulation covers the entire building shell, except under the slab floor. This layer of high R-value is two inches thick in the walls and three inches thick in the roof. The foam creates a continuous barrier to air leakage.
There is no ventilation in the cathedral ceiling. The technique is called a "hot roof". The layer of spray foam is impermeable to water vapor and the surface of the foam stays warm enough that vapor will not condense. In other words, the surface temperature never falls below the dew point.
Foam easily fills tight spots where batt insulation is difficult to install. These include corners, headers, small cavities and around obstructions such as pipes and wires. Also, foam seals the bottom plate to the subfloor, one of the most troublesome air leaks to fix.
After the thorough foam treatment, the only places left to caulk were around the window and door rough openings.
The remaining space in the cavity is filled with Bonded Logic Ultratouch batt insulation made from recycled denim. Cotton has no itch and no formaldehyde. However, there is still enough dust to warrant a dust mask and safety glasses when working overhead.
Some places are quite a stretch.
Cotton batts are visible in the walls.
The only difficulty working with cotton batts was cutting them. A utility knife is slow and leaves a ragged edge. The best tool is a small battery-powered circular saw. It speeds up the work immensely.
Earth Advantage residential specialist, Suzy Randles, performed a blower door test that measured the home's air leakage rate at an astounding 0.09 air changes per hour (natural). Although air leakage rates vary widely, typical construction is generally around 0.4 ACH, while 0.2 ACH is considered very tight.
How did it get so tight? The spray foam approach is the main reason. Tight windows -- most are either fixed or casement -- is another reason.
