Insulating an older (1970) insulated attic
I have had a company quote damp cellulose insulation installation. They will install soffet baffles and blow in 16″ of insulation, 1158 sq ft, $3995. No air leak fixes. They will cover the whole-house fan that exhausts into the attic with pink insulation. They will not insulate the drop-down ladder. After reading your and others websites, I believe $3995 is expensive.
I have decided to fix the air leaks myself: fan, stairway, 2 stack pipes, and septic vent pipe.
My question: After I blow in the insulation (I’ll try to compact it by blowing toward the rafters), would it be all right to staple 4 mil poly over the cellulose insulation to further compact and further restrict air movement thru our ceiling??
We burn wood in winter and AC in summer. We live in Grass Lake, MI, south of I 94, east of Jackson, MI.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Are you installing 16" of cellulose at the RAFTERS (under the roof deck with 1" of soffit-to-ridge venting in every rafter bay), or on the attic floor, between and on top of floor joists?
If there is going to be any 4-mil polyethylene anywhere in the stackup it needs to be on the warm-in-winter side of the insulation.
Billie,
No, you don't want to install polyethylene on the top of the cellulose. It will trap moisture and lead to problems.
Here are links to three relevant articles:
Air Sealing an Attic
How to Insulate an Attic Floor
Borrowing a Cellulose Blower From a Big Box Store