dense pack cellulosePosted: October 16, 2012
The primary objectives of our rehab have been heat and weatherization. The latter has been accomplished by creating an eight inch wall cavity, filled with dense pack cellulose insulation.
After the demo of the lathe and horse-hair plaster, we built a new inner wall using 2×4 studs. We then attached a fine mesh cloth to the studs, and applied 1 x 3 pine strapping. The strapping would hold the mesh firmly after the cellulose was blown in place.
This photo (to the left) shows the mesh before the strapping. The photo to the right shows the strapping applied, and the cellulose being blown in place.
Cellulose is made of 80% post consumer recycled newsprint (we have gained a new respect for our print journalism family members!) treated with borates to resist fire, insects, and mold.
The Building and Construction Technology group at UMass Amherst has done studies on cellulose and reports “insulating a 1500 sq ft house with cellulose will recycle as much newspaper as an individual will consume in 40 years.” (Our house measures 1300 sf).
When I asked how stable cellulose was, the crew chief said the cellulose “will last as long as the house.” Dense pack cellulose – blown into place by high-powered fans – is effective at blocking air leakage through cracks, holes, and gaps. Our 190 year-old house had plenty of those.
The r-factor of cellulose (the rate at which heat is transferred through the cavity) is rated somewhere between 3.7 to 4 per inch of wall cavity. Because our inner wall studs do not line up with the old exterior studs, (the new studs are 16″ on center, but the old studs are at odd intervals) the thermal bridging is reduced. If the inner studs matched the outer studs, we would have a series of 16″ cavities. In our house, however, the new and old studs do not match up, creating a thermal cavity with more area, thereby creating a greater insulated mass.
At 4-r per inch we should surpass 30-r, putting us into the super-insulated category. I am told.
We blew the cellulose into the walls, the attic, and the crawlspace. Our attic insulation achieved an R-factor of 60.
Prepping the crawl space was a dismal task. A dirt floor, 16 feet long by 5.5 feet wide, with varmint holes below and spider webs above, I had to crawl into that space to apply the mesh netting. (I kept wondering if a gopher would poke up its head!) The space varies from 18″ to 9″ high – a wicked tight space to work overhead, lying on your back. For three hours.
It wasn’t much of a choice. Applying no insulation would leave a cold zone along our bedroom floor. That work achieved an R-factor of approximately 20.
On a cold January morning that will have been well worth the effort!
Next I plan to lay 10-millimeter plastic over the dirt floor to create a vapor barrier. Eventually, we will apply spray foam insulation to the brick walls of the crawlspace to create as tight an insulation as possible.