Attic insulation
I have 20 year old home in SC that has fiberglass batts between ceiling joists and a few years ago I had blown fiber (12 inches) on top of that. However the area over the attached garage has never been insulated at all. Since we are having record heat I’ve decided to insulate the garage area since yesterday it was over 100 degrees in the garage. I am not sure that I am getting full benefit out of the
existing insulation due to pot lites and perhaps the soffit vents may be blocked or partially blocked.
I had an insulation contractor come out today and he wants to rake the insulation down where it may be blocking soffit vents and placing a product that is composed of bubble wrap that has foil on both
sides and caulk and seal the the underside of the rafters to about 18 inches from the ridge vents. This material is to seal the entire attic space thereby negating the effect of pot light penetrations etc. In other words he wants to seal it from top plate on exterior walls to with in the area just below the ridge
vents channeling the air that is radiated through the roof up to the ridge vent. He is not recommending putting insulation in over the garage.
I hope you can make sense of this and can give me your opinion on such a procedure.
thanks in advance
Jerry Harris
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Replies
I think you should consider an energy auditor
including blower door test and IR Camera...
I agree with John on having a more thorough diagnostic done by someone who is not selling an insulation product.
What the insulator is selling is mostly a radiant barrier, and although that approach is not in use here (heating climate, little/no AC) it apparently does have some merit in sunny cooling climates, which apparently you have.
HOWEVER... the bubble foil product in this situation makes no sense to me. Why the bubbles? Does he claim he can create a conditioned attic by stapling this product to the bottom of the rafters and sealing it around the edges? Does he claim he can move the pressure boundary up to the rafter line? I am really skeptical of this part. I do think the RB might have some minor benefit. but it doesn't need the bubbles, and there's no way he can build an airtight bag in your attic with this stuff.
The vent channels from the eaves to the ridge... you want those, but all you need for that is baffles that keep the insulation from spilling out against the eave vents. The person who installed the blown-in should have installed those, typical cardboard or plastic chutes. I can't imagine why they were omitted.
I would tell the radiant barrier/attic bag guy you don't need it. Find someone who will perform blower-door-guided air sealing of your attic floor. They set up the blower door to pressurize the house, then go in the attic, move insulation out of the way in small sections, and find the air leaks. They use canned foam, caulk, rigid insulation board, sheet metal, and whatever else to seal the leaks.
The can lights might need boxes built around them, or consider replacing them with IC/AT types with air-tight trims (solid lenses are best in my experience). Make sure the insulation is uniformly distributed and shoot for 18" thickness or more (yes, thinner at the eaves because it has to be).
As I said, there may be some merit to a radiant barrier, but not in the form of bubble foil. If you find the right insulator/home performance guy (you'll know when you see the blower door and hear them talk about air sealing) ask them about RBs.
You could have the garage attic treated in a similar manner, and it would probably reduce heat flow into the house to a small degree, assuming the wall between the house and garage is minimally (or not) insulated.
Thank you David, I had misgivings about the RB. I appreciate you taking the time to get me
running in the right direction.
Jerry