Blown Cellulose Insulation: Passive House Insulation
|use of spray wet cellulose in passive house|
Beyond using SIPs and Superior Walls as our initial exterior insulating material, and selected amounts of spray foam insulation (primarily for air-tightness), we selected blown-in "wet" high-density cellulose as our additional insulating materials within our secondary interior studded wall system.
Blown cellulose offers many advantages over other insulation media:
- Cellulose is extremely cost-effective (even though its R-value is somewhat low)
- Cellulose is environmentally friendly consisting of approximately 80 percent post-consumer recycled material, such as newspapers and blue-jeans
- While not strictly airtight, cellulose provides an level of air sealing other conventional insulation (like fiberglass batts) does not
- Borate treated cellulose, itself, has the highest (Class I) fire safety rating
- Cellulose enhances fire-resistance to the building, as it nearly eliminates the primary food of fire, air--behind the wall and in the cavities between the studs
- Borate treated cellulose offers a level of insect control
- Cellulose adds additional levels thermal mass
- Cellulose improves sound-deadening
- Spray-applied cellulose (wet-spray cellulose) improves airtightness, density, moisture (ie; mold) resistance, and potential settling issue
- Cellulose has extremely levels of embodied energy (energy used for its manufacture)
- Cellulose uses no VOCs, CFCs or HCFCs and does not off-gas, for improved interior air-quality, especially important for air-tight passive houses
We also chose to spray cellulose within all of our interior walls as well, to further increase thermal mass and to offer additional levels of sound-isolation between the rooms. To further help in sound-deadening of the drain pipes over head in the ceiling of the first floor, we netted the floor joists and filled them as well.
One additional point worth nothing: Using this material added a significant amount of moisture (humidity) inside the conditioned building envelope. Since the home was already air-tight and given the time of year, we relied on using de-humidifiers and fans to speed up the drying process (more on humidity levels in a later article). For a time, RH percentage levels increased to the mid-to-upper 60s and even >70% for a short period and required close monitoring and management for a short-time.
However, between the 5/8" drywall and the use of sprayed (wet) cellulose, we built a fortress. Of all the energy efficiency initiatives during our construction, I believe its use provided the biggest bang for the buck.