Guest User
8/5/2004
We would like to replace our asphalt shingle roof with a metal roof. Is the use of a radient barrier underlayment a good idea? Is the addition of insulation as an underlayment a good idea? We live in North Carolina. Thank you!
Guest User
8/5/2004
Every job must be looked at individually, especially in regards to insulation. However, yes, I feel that radiant barriers are helpful. However, the shiny side must face an airspace in order to be effective. You might also talk to the manufacturer of your roofing and ask them what suggestions they have for creating an efficient system,/ Some manufacturers are using coatings with special reflective pigments. Generally, in regard to insulation, I would much prefer to see insulation down on top of the ceilings and then have good ventilation above that rather than try to add insulation on the roof deck.
Guest User
9/14/2005
What about laying 1X4s every four feet, then laying the radiant barrier, then laying additional 1X4s on top of radiant barrier, and last laying the metal roof? Would this add enough airspace in your opinion?
Todd Miller
Classic Products, Inc.
9/14/2005
This would create a fairly "dead" airspace which is helpful, especially in regards to blocking heat transfer by conductance. However, it does nothing in regards to venting excessive moisture. To truly get rid of unwanted heat and moisture, you must have a vented airspace, meaning that you have intake and exhaust vents.
Jim B
6/1/2006
On the insultion thing. . . I think I will finally get the Fabral SSR put on my garage (my garage could be the ultimate reference for Ice & Water shield) and - having chosen a dark grey finish - I would like to find a way to block heat from coming into the attic through the roof. I bought aluminum foil bubble wrap (radiant heat) and was thinking about suspending it a couple of inches below the underside of the roof and stopping short of the vented soffits. When finished, the house and attached garage will incorporate Hardi vented soffits at the eaves, Fabral vented ridge at all peaks, and as much gable vent as I can fit in. I would still use a kraft-backed R-38 fiberglass in the ceilings with poly styrene baffles to keep the insulation from blocking the soffits. My question is: Will my foil insultion reflect the radiant heat coming through the roof back out? or will it super-heat the plywood underlayment? And since the bubble wrap is supposedly a vapor barrier, will condensation collect on top of the bubble wrap and run down the slope onto my fiberglass? Or should I just put the buble wrap on top of the drywall ceiling, then lay un-backed R-38 on top of that?
Allan Reid
Dura-Loc Roofing Systems, Inc.
6/2/2006
I would suggest reading the building code and understanding their requirements for roof assemblies. They call for an interior vapour/air barrier to the warm in winter side . 10 mil poly is best and use accoustical caulking to seal all laps and penetrations. They have a minimum for insulation and an R38 is good. You then must ventilate between the insulation and roof covering. For attics it is 1 sf for every 150sf of ceiling are and it is to be balanced 50-50 bettween riudge and eave or it will not work. Gable vents wiull short circuit the air and leave hot spots. Do the calculations and adjust axccordingly. The code also calls for a moisture barrier under the roof covering to act as a secondary mebrane and to deal with any condensation. Fellt paper is the minimum.
Guest User
6/7/2006
. .not sure why I can't log in, but . . . anyway. . . My issue is trying to keep the sun's radiant heat from going through my (dark charcoal colored Fabrall SSR) rood and heating my attic. The tech 'stuff' from the bubble foil insulation people say to run the foil from ridge pole (continuous Coravent vented ridge) to vented soffit. This makes sense to me as the intake should come through the soffit and be funneled between the roof decking and the foil, up to the ridge and out. However, the space between the R38 fiberglass on top of the room below's ceiling drywall and the foil would then be unvented. Would gable vents still short-circuit the flow, or would the foil insulation create two 'zones'? Or should the foil insulation be layed between the roof decking and the standing seam panels?
Allan Reid
Dura-Loc Roofing Systems, Inc.
6/16/2006
The first two principles is to follow the building code and the roof manufactures recommendations. You must ventilate the attic space between the insulation and the roof covering to a minimum ratio of 1 sf of free air for every 150 sf of ceiling area and it must be provided 50% at the eave and ridge. This is the most important aspect of the roof to save energy and remeber it is minimum. Gable vents and power vents do not count as they short circuit the air flow. The foil then over the decking will do little unless it has a vertical vented free air space on minimum 1" and then it is the air space doing the savings not the foil.
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