Board sheathing air-wash?
I am remodeling a Victorian house with board sheathing in Vermont, I have added a second row of studs making my wall about 8″ thick. I am going to do airtight drywall.
The cellulose guys want a LOT to insulate, but I am concerned that if I use fiberglass, air-wash will get through the board sheathing into the fiberglass. Can I Tyvek the inside of the sheathing? (Tearing off the clapboards is not an option. It would clearly be labor-intensive, but I would do the work myself.
The attic is going to be really well sealed inside and out, so I’m less concerned about using fiberglass there.
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There is no practical way to install Tyvek on the inside of the sheathing.
To improve the airtightness of your sheathing layer, you have several options:
-- dense-packed cellulose;
-- Owens Corning Energy Complete system or the similar Knauf system (Ecoseal);
-- Flash-and-fill, using 2 inches of closed-cell spray polyurethane foam.
Johns Manville claims it's possible to dense-pack blown-in fiberglass: "Dense-pack JM Spider for drill and fill" for retrofitting existing walls:
I don't know if this is marketing hype or a good approach.