metal over hot roof

mark allegrezza
Hi, I am wanting to add a metal roof over my existing hot roof. The roof is 2x6 tounge and groove (car decking) running the legnth of the 4-12 pithced cathedrial roof. With about 3 inches of fiberglass board over that, and then tar and gravel over that. It has held up well for being built in the fifties, but has cracked down the whole ridgeline which i have temporarily fixed with a ridge cap. I was thinking of bulding it up with a little more foam board insulation and a little air space in there, but am really not sure how to secure through the existing insulation? I was not wanting to tear the existing roof and insulation off, but was going to do a little patch work first in a couple places instead. But should I just screw or lag threw the existing insulation into the car decking? Any input would be appreciated. Thanks, Mark
Todd Miller
Isaiah Industries, Inc.
I would encourage another layer of decking over the new insulation and airspace and yes that would have to be lagged through to the tongue and groove. Perhaps others will have some other thoughts. You may want to consult a structural engineer as this is really more relevant to them than to metal roofing specifically.
Eric Novotny
An informed customer is the Best Customer!
While the removal of the existing roof will be a tangible expense, in a perfect world, I would prefer to see that removed down to the T&G decking. and ideal world, here is what I would propose: -remove existing roof to T&G decking -install ice and water over to T&G to air seal -installation of R-25+ insulation layer direct to covered T&G deck -installation of purlin/batten to create over deck airspace (screen vents on both eave and ridge to prevent any infestation) -installation of new deck (plywood deck) -installation of new roof That is my utopian approach. Work within normal ranges I would recommend Todd's approach. Another layer of insulation, deck, and air space.

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