do you need a vapor barrier with cellulose insulation?

J

Do I need a standard 6 mil poly vapor barrier with dense cellulose exterior wall?

jeff Chormann Published: May 1, 2020, 9:18 a.m.Last updated: May 6, 2020, 3:09 p.m.

I'm renovating a 1915 bungalow in masachusetts with no  existing wall insulation. I've opened the wall cavity and plan to use a dense pack cellulose to achieve R-14.  The exterior wall is plank sheathing with paper wrap, followed by shingles, then 1/2 celotex foam board and vinyl siding installed in the 1980's.  No rot or leakage is visible from the inside.  My question is if I install a poly barrier over the cellulose on the inside under the drywall,  will I then cause vapor to be trapped between the outside vinyl /foam board and poly barrier.  The foil faced foam board is  not completly tight against the underlying shingles and I assume does allow for some air movement underneath it and  the vinyl siding. 

Thanks

Responses (1)

G
Gregg Tate May 20, 2020, 10:39 p.m. Reply

Personally, I think I would be very cautious in changing your current wall, and i'd probably chose Rockwool over cellulose, then use a smart breathing membrane instead of straight poly