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TOPIC: Installation Process

Felt underneath metal?

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When roofing installed, is it necessary to put felt underneath metal? I have heard so many different opinions...but what to do?
Guest User

9/27/2004
I would never put down any roof without an underlayment. Check with the manufacturer for details.
Guest User

9/27/2004
can you use polarium underneath standard composit (ie. pro 30) type of shingle in place of felt? If so, do you place the foil side against the decking like you would do with the metal roofing?
Guest User

12/23/2008
I am not familiar with polarium. I take from your post that it is a radiant barrier though and in general radiant barriers do not do well in a "sandwich" situation -- they need to face an airspace. Also, one of the reasons I prefer underlayment is so that the rough surface of old shingles does not rub against the back side of the metal roof panels. Todd Miller
Todd Miller
Isaiah Industries, Inc.

12/23/2008
Richard, You can install polarium under your shingles. We still put down 30 lb. felt first though. We have used polarium quite a bit. It's not anything I try to sell, it has been at the customer's request. I am like Todd, I can't see it working against a solid deck. The president of Polarium sure does a hard sell though, he showed up on a job we were doing in Odessa, Tx last spring. I still don't want to use it and one last thing, the foil side does go down. [email protected]
Guest User

12/23/2008
Why is Polarium not a product you would use? I have had it recommended by several contractors. They make the claim that it is a radiant barrier that will save on heating and cooling.
Guest User

3/14/2009
Sharon, If I understand the concept of a radiant barrier, there is supposed to be an airspace between the radiant side and the attic. With the Polarium "sandwiched" between the roof and the deck, I have a hard time understanding how it could work. It appears there definitely would be heat transfer. It appears as though the Polarium could not reflect anything this way. You can look at an expensive aluminum window, one manufactured with a thermal barrier. There still is a heat/cold transfer from the outside to the inside, although not as much as a solid aluminum window. Therefore, the Polarium would act as a resistant to the transfer, but anything between the roof and the deck would, be it a dead air space or ice and water shield and to a lesser degree, even felt.
Guest User

3/15/2009
Thanks Wade Todd Miller
Todd Miller
Isaiah Industries, Inc.

3/29/2009
All Radiant barriers have to have an airspace, they become a conductive building layer once anything is pushed up against them. They have spray applied products for the underside of the building package in the "attic" space. They are made to be permeable so there are no water condensation build up problems.
Guest User

6/29/2010
It will not work between shingles and deck without an air space facing the aluminum coating.
Guest User

11/3/2010