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My house (in Orlando, FL) has a vaulted ceiling over the 2nd story with no attic space above the living space making it impossible to insulate using traditional insluation.
I am considering a metal roof (tile or shingle shake) due to it's energy efficiency and the perceived ability to insulate above this room. However I have spoken with several contractors and am getting information that conflicts with what I think I have read on this forum. One contractor told me that the metal roof itself (Decra) has reflective capabilities built into it and will reflect most heat giving it a R19 value. He also said I could put foam board under it that would add an R10 value giving it R29 insulating value.
Another contractor told me that the same product has no reflective capability and that he recommends installing a radiant barrier on top of the underlayment then laying 2" battens on top of the barrier and putting the metal tile on top of that. From what I have read about radiant barriers I thought you needed 4" of space minimum. He also said putting foam under the roof would only delay heat transfer not prevent it.
I am obviously confused. I have read that the newer metals can have a reflective coating that will indeed reflect heat so I'm not sure what to believe. Would it be possible to get a recommendation for the best way to install a metal roof so that it would reduce the heat transfer into my house?
Thanks,
Steve
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Hi Steve, great questions. And, you're right, a lot of confusion surrounds this issue.
First of all, the "actual" R Value of any metal roof will be very minimal. However, certain systems do have reflective properties which can provide an "apparent" R Value during sunny daylight conditions. Additionally, metal roofing lends itself well to ventilation in many cases which can play a huge role in efficiency as well.
Yes, many painted products are now available with coatings utilizing reflective pigments so that, even in dark colors, total solar reflectivity of 25% or more can be achieved. I believe that some of the stone coated products are using these pigments as well. Always turn to the manufacturer if you need a "final answer" to a question.
Also, light colored products will often have reflectivity of 50% and more.
Now, some metal roofs including many of the stone-coated products, can be vented directly beneath the metal by placing the products up on battens. To be really effective at that though, you need vertical battens first followed by horizontal battens. The resulting vertical airspaces can then be vented with soffit vents as intake and ridge vent as exhaust. This is very effective.
I will also say that many of the shake and tile profile products, even if not up on battens, have some good inherent efficiency because of the dead airspace which, to a large degree, separates the metal from the roof deck so that heat is not conducted from one material to the next.
As far as radiant barriers, yes, they need to face an airspace to be effective. Larger airspaces I believe will help the efficiency but the main thing they need is to not have direct contact in a "sandwich" between materials because the radiant barriers will conduct heat if they are in a sandwich. Additionally, if the radiant barrier faces a vented airspace, that is helpful.
Please note that Decra is not a member of the Metal Roofing Alliance. You may wish to check out the products produced by our member manufacturers as well.
Warmest Regards,
Todd Miller
10/27/2005
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Or copy this URL: https://www.metalroofing.com/spirit/comment/6963/find/Isaiah Industries, Inc.
10/29/2005
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