Attic airsealing options with existing floor

Old 03-13-19, 05:08 AM
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Join Date: Mar 2019
Location: USA
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Attic airsealing options with existing floor

I have a 1961 rancher in Maryland. The attic is underinsulated with a combination of unfaced fiberglass batts on top of some old brown foil-faced batting (approx. R19 total) and I have condensation on roof nails due to warm moist air making its way into the attic. I would like to airseal and add blown-in cellulose insulation to get to at least R49. About 1/3 of the attic has 3/8" plywood flooring, some is a storage area and some runs along the length of the attic to provide an area to stand while servicing the AC air handler and ductwork. I will probably remove half the flooring and no longer use the attic for storage, but I still need easy access to the air handler and ductwork so some flooring needs to remain.

I've had 2 insulation contractors come out and make recommendations and provide estimates. First guy wants to remove all the flooring and existing insulation, airseal all penetrations into the attic, and then put whatever flooring is needed back and "dense-pack" the cellulose under the flooring. The non-floored area would be traditional blown-in cellulose. This guy wants to put in R60 where possible.

The 2nd guy suggests leaving whatever flooring I need and filling all the floor seams and openings with spray foam, as well as damming the open sides of the flooring between the joists to seal, then blow cellulose over top. This method sounds attractive to me due to the reduced labor involved, but I can't help but think that any warm air that gets into the attic under the floor will be trapped by the flooring and damming and cause moisture. He also says anything over R49 is overkill.

Am I correct in my thinking regarding the warm air being trapped under the flooring in the 2nd option? Is going to R60 going to give that much benefit over the code-minimum of R49?
Old 03-13-19, 06:32 AM
Join Date: Oct 2008
Location: New England
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Code minimums are based upon the cost of energy. If energy costs go up then you should have installed more. How is your crystal ball doing? I like r-60 especially where and when it is easy. Compare that to making your walls r-60. Not going to happen yet it would be basically the same savings.

The real issue is leaving a wood floor up there in any form. With good ventilation that attic will be close in temperature to the outside. Any air from inside the house will be loaded with moisture and if that reaches a cold enough surface then condensation will result. The best approach would be to elevate the walk area above whatever you install for insulation below it, even if it is just the r-19. Creating a space between the insulation and the walkway provides an escape for that moist air.

But as you have said, air sealing is the objective and that can best be done with the current insulation removed or at least moved to the side. I like to see the old removed, everything cleaned up, and then new insulation installed for many years of comfortable living.


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