Type of insulation
We are building a brick home with 2X6s wall. With OSB sheathing covered with tyvek. The mechanical is almost complete. We will have geothermal heat. We live in central Illinois.
The plan for the walls was 2″ closed cell foam with the remainder of the space filled with dense-packed cellulose. Our budget is being squeezed, and I am considered filling the 2×6 walls with 100% cellulose or the BIB fiberglass. We have already had the furnaced sized based on the calculations of the form. I still plan to use the foam on the rim joists, so I am worried that the dense-pack cellulose will allow for air infiltration. Also from reading on the forum, Cellulose can be a problem for a broken pipes..
Sorry my question: Will going will there be a significant increase in air infiltration by going with all dense cellulose or BiB fiberglass. Will the increase cause me to increase the size of my furnace. Should I bite the bullet and stay with my original paln.
Thanks,
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Replies
I think you mean you're building a wood-framed home with brick facing. I trust there is a ventilation gap behind the brick with weep holes or other means of drainage at the bottom. OSB is the worst choice of sheathing, particularly behind a reservoir cladding like brick which can hold large quantities of water, and Tyvek is the worst choice of housewrap because it has the highest vapor permeance.
But, if the exterior details are well-designed and well-crafted to avoid exterior moisture intrusion, and the house is new and built tight and well-ventilated, then either the Flash-n-Fill or dense-pack systems of insulation should work (though, if you're in climate zone 5, you will have trouble getting R-20 in a wall full of thermal bridges).
Other possibilities include interior rigid foam board with dense-pack behind it, or cross-hatched framing (horizontal 2x3s inside the studs) with dense-pack - but either of those will slightly decrease interior space.
There are several ways to create an tight envelope, including careful detailing and caulking of drywall and air-tight electrical boxes.
None of these options should have an appreciable effect on furnace sizing. And no insulation or wall system survives a major plumbing leak - that should be the least consideration in choosing (there shouldn't be supply pipes in an insulated wall).
Philip,
I agree that you chose the wrong sheathing.
Your walls will be subject to inward solar vapor drive during the summer. As long as you don't install interior polyethylene, your wall will probably work. But it's always best to include foam sheathing instead of OSB behind brick veneer. Foam sheathing would have reduced the danger of inward solar vapor drive, would have reduced thermal bridging through the studs, and would have improved the thermal performance of your wall.
That said, 5.5 inches of cellulose isn't much insulation -- about R-20 in the stud bays, a number that will be reduced significantly by thermal bridging through the studs.
I would advise you to install cross-hatched (horizontal) 2x3s as Robert suggested -- or borrow the money for the closed-cell spray foam.