Installing Foil radiant barrier
jrs48073
| Posted in Energy, Heating & Insulation on
hello everyone, I’m new to this discussion group and a novice do-it your selfer.
I live in Royal Oak Michigan and have a hot 2nd floor ceiling (I have a tri-level) and want to reduce this thermal load for better cooling.. the asphalt shingle roof has roof vents, gable vents, and sofit vents. I have ~ 6 inches of FG insulation. I’m thinking that a radiant barrier (Foil-foam-foil from Prodex) is a good solution before I invest in more insulation.
Do I install the foil flush to the roof decking or leave an air gap by attaching foil to the rafters?
I’d appreciate any comments and suggestions.
Jay
Replies
On the rafters. But, this stuff is a vapor barrier. Are you going to be all right with that?
I'm not so sure of it's performance. The r-value claims fluctuate and seem to be a bit generous. No real firsthand knowledge but picked this up keeping my ears open.
6'' of fibreglas isn't a large amount. Are the ceilings flat with rafters above or is some of the upstairs ceiling clipped with the ceiling on the rafters?
A great place for Information, Comraderie, and a sucker punch.
Remodeling Contractor just outside the Glass City.
Quittin' Time
You need an airgap of at least 1/2 inch to have the radiant barrier to work. The Tyvek site shows Mike Guerten of FH installing a new Tyvek radiant barrier. You might be better served by insulating more in your attic.
Hi,
It needs an air gap to work.
Here is a bit of info on installation and benefits:
http://www.builditsolar.com/Projects/Conservation/Southface14radiantbarriers.pdf
Gary
Jay,
You would get better performance by blowing cels over the existing fiberglass. It would block both radiant and convective gain.
Do a search on BT, lots of info.
KK
Close off the gable vents.
Look at the paybacks in Florida where there's a lot more cooling to do!!! Leave the venting as is and add more blown cellulose insulation (up to R50) after airsealing the attic. The extra will save on winter heating bills also.
http://www.fsec.ucf.edu/bldg/pubs/cr978/#Economics