metal over shingled mobile home

jody tillman
8/11/2011
I plan to put a metal roof over the existing shingles. I will be using 29 ga. Classic rib painted metal. I have a ’99 manufactured home. Most of the ceilings slope with the roof (4 ½ pitch).The 2x6x14 rafters span from the exterior walls to the center wall, with drywall on the bottom of the 2x6 & 3/8” or 1/2” plywood, felt, and shingles on top with insulation in between. One room does not have center wall &is open between exterior walls. Needless to say, the roof is a little springy to walk on and is a little wavy which I guess is expected with m.h. Most people in the area install this metal over their existing shingles using 1 x 4s, 2’ o.c. w/out an underlayment. I see that I need to use an underlayment. I’ve been looking at different products and I am confused on which is best in this situation. The metal supplier sells 1/4" solar guard insulation. I have also looked at Prodex Total, single & double bubble insulation. All of which are expensive. Would I benefit that much from these or just use a synthetic felt? Should I be concerned with adding more weight and remove the existing shingles? If I do need to remove them, would the type of underlayment change? Also in my situation, do I need vertical 1 x 4s also?
Todd Miller
Isaiah Industries, Inc.
8/12/2011
My personal feeling is that if the metal roof you choose is light colored or has reflective pigment, these special underlayments may not accomplish much extra for you. That is just my opinion though. The underlayment manufacturers will probably disagree. Cross battening with vertical 2 x 4's first will allow some true convective airflow and ventilation. This will help tremendously with reducing summer cooling loads and avoiding the possibility of winter ice dams (though you may be too far south for that).
Eric Novotny
An informed customer is the Best Customer!
8/13/2011
All Radiant barriers need an air space to work properly. I agree with Todd that an air space will probably do more good than the radiant barrier will, however, if you get it cheaply enough it can't hurt.

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