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Gibbyplease · 11-01-2009, 06:25 PM

My smallish attic has 3.5 inch foil-faced batts between the joists. Some more insulation would obviously be a good idea and I plan to add R30 unfaced batts which are often available at Lowe's for 30 cents/sf (I'm in the Pacific Northwest). There is conduit and romex running here and there (which I don't imagine I'll need to access in the future) and the previous owner has used all sorts of odd bits of plywood to basically put a partial floor in above the joists (approx. 40% of the space).

Would it be okay to just lay the new batts down over the top of the plywood? Or would it be better to remove what I don't need?

ccarlisle · 11-01-2009, 08:22 PM

The foil on the batts acts as a vapour retarder, which in you area should be on the outside of the insulation. You risk wetting the new insulation...

Gibbyplease · 11-01-2009, 10:13 PM

Not sure I follow.
The foil is face down against the lath & stucco ceiling. Any additional fiberglass would just thicken the batts and all would continue to dry to the outside, under the ventilated roof.
Unless what you're saying is that the foil should be removed entirely and replaced with a lower-perm barrier, i.e. kraft paper?

ccarlisle · 11-02-2009, 07:07 AM

Oh, face-down is it? Well then OK, you can place new unfaced batts over that in the opposite direction from the frst layer.

Sorry, I just thought they were face-up...

Maintenance 6 · 11-02-2009, 07:37 AM

Regarding the plywood. Ideally, you should remove it. You don't want any air gaps between the original insualtion and the new. And don't insulate tight against the underside of the roof along the eaves. Allow about and inch and a half air space below the roof deck.

ccarlisle · 11-02-2009, 07:41 AM

yeah, good point...the plywood doesn't serve any purpose apart form preventing you from going through the ceiling below. Useful, but not required in your project.

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Attic insulation: clean before?

Attic insulation: clean before?

Attic insulation: clean before?

Attic insulation: clean before?

Attic insulation: clean before?

Attic insulation: clean before?