Insulation factor of space between roofs

Guest User
7/14/2003
What is the R factor of the space created when installing a metal roof on a 2x4 strapped old metal roof? Is insulation in the gap even worthwhile? Fred
Todd Miller
Classic Products, Inc.
7/15/2003
An airspace has no R Value. If you put insulation in this space, then the R value will be based upon the type of insulation you use. I'd need to know more details on your overall construction but insulation directly beneath a roof panel or a roof deck can sometimes create an opportune space for moisture to condense. If you wish, call me to discuss. Todd Miller 800.543.8938 ext 201
Guest User
7/22/2003
I want to install a metal roof over my existing composite roof. We live in Tampa, FL. I have met with two different sales individuals. For the interlocking metal roof with stone granules covering the metal a polystick product was recommended to maximize reduction in air conditioning costs. The second individual was selling verticle solarshield metal roofing and recommended Fi-Foil radiant barrier. Can you comment on these two products.
Allan Reid
Dura-Loc Roofing Systems, Inc.
7/22/2003
Hi again. First off you need to determine if you have an attic or not. If you do the most important thing to do is to provide adequate ventilation. The next most important item is to choose a light colour roofing as it will reflect a higher portion of the suns rays and last ensure that it has ahigh emittance which means that what did not reflect will emitt back out. Same goes for a vaulted ceiling. The new US Intenational building codes call foe a minimum of 1" free ventilate air space over the insulation and under the roof covering. A metal roof installed on wood battens will meet the code here. As I am a manufacturer of both granular and painted metal I can as`sure you that metal has the solutions. Hope this helps.
Guest User
6/20/2005
Todd - I am in a similar situation. I have a 3" tectum ceiling/deck with two existing asphalt shingle roofs. I am considering having 2" of polyiso foam insulation that is approved for installation directly on the roof deck without a thermal barrier. The insulation would be placed on top of the existing shingle roofs in between 2x4 lathe boards every 2-3 feet apart. The 26 gauge metal Akzo 950 painted galvalume roof with a "R" design would be screwed to the lathing. I forgot to mention that I live in Alabama in a Frank Lloyd Wright inspired home with exposed beams and no attic ventilation b/c there are no soffits for air to come in through. Do you foresee any issues with this setup? Thank you so much. bhk
Todd Miller
Classic Products, Inc.
6/20/2005
This does not allow for a vented airspace but, ultimately, it will make the situation better than it is currently. You could work a 1" vented airsapce into this assembly, directly beneath the metal, perhaps.
Guest User
6/20/2005
Thank you for the response. Does this mean that you might try a 1x2 on top of a 2x4 with the 2" insulation? Would this setup potentially cause a weight issue? Just so you know, our exposed beams are at least a foot tall by 4 inches wide and are made of cedar. Thank you very much. bhk
Todd Miller
Classic Products, Inc.
6/21/2005
You may need to get a structural engineer involved to do some analysis. Ultimately, any airspace you add should have vertical flow so that you can work in eave soffit vents as intake and a ridge vent as exhaust. One way to do that would be to put down vertical boards next and not fill them entirely with insulation but leave a gap for venting, and then put on horizontal lathe (or solid decking) followed by metal roofing. (Underlayment first if you install solid decking.)
Guest User
6/21/2005
Thank you for your insight, Todd. bhk
Todd Miller
Classic Products, Inc.
6/21/2005
Sure. Good luck.
Guest User
6/22/2005
Todd - What do you think about PRODEX High R (FfmF) Foil-Foam-Foil insulation instead of the 2" foam insulation? This way, I could have a R-14.3 instead of R-12.1 with only 1/4" of thickness. It says that it is unaffected by moisture, and it better holds it's R-value vs. fiberglass in humid conditions. Could this be placed in between the asphalt shingles and the metal roof as previously planned? This would leave more than enough room to meet the 1" minimum for venting. Thanks for the additional help...I need it.
Todd Miller
Classic Products, Inc.
6/22/2005
This type of product would probably work. Double check with the roofing manufacturer to make sure they are okay with it.
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