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Will sprayfoam work here? Post New Topic | Post Reply
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Circle-D
Posted: Dec 06, 2006 06:51 PM
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Will sprayfoam work here?
I had a customer come to me today with a problem. She had a metal roof installed on her home a few years ago. He installed an addition to the building and changed the roof pitch some. He roofed right over the existing shingled roof of the building and over the open rafters of the new addition. He did not put any vapor barrrier under the metal. This is a vented roof. When the weather turns colder (15 degrees or so the last 3-4 days), the metal of course gets condensation on the bottom side. I suspect the filterglass insulation in the ceiling is letting enough heat to escape to melt the frost on the bottom side of the roof. This in turn soaks thru the filterglass insulation and drips thru the joints in her V-match knotty pine ceiling.My question: If I were to peel the roof off(next summer of course)and spray a layer of foam over the existing shingles of the old roof and onto the back side of the knotty pine in the addition, (after removing the wet filterglass)then reinstall the metal, would that seal and waterproof the building? Would I also need to install a vapor barrier between the foam and condensating metal roof? Would I be better of with just a vapor barrier, no foam? What would the experienced foamers here do with this situation? Thank you for your input. Skip |
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Melvin Chandler
Posted: Dec 06, 2006 08:41 PM
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I'm not an experienced foamer but I do own a 30 year old roofing company that has TONS of experience with this application. 1. Metal roof systems are not waterproof. There is no metal system that is seamless unless all joints are soldered. Much like slate, tile, shakes, etc., it's the roof below the roof that protects the structure. 2. Metal should never go over shingles just like foam should never go over fiberglass. 3. Wood strips should never go over shingles so as to allow for metal installations. The proper thing to do would be to pull the metal off to the deck and install an Ice & Watershield type product and then install the metal directly over it. On the open framed area; install a solid deck, Ice and Watershield and then put the panels back on. Otherwise, spray closed cell to the bottom side of the metal on the open framed area. As for foaming the existing structure, you probably could spray between the wood strips and then put the metal back on but I'm all for starting over and getting it right to begin with and not looking for alternatives to try to correct a bad situation. |
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Circle-D
Posted: Dec 07, 2006 08:55 PM
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HMMN.........interesting. Thank you,Newby for your response. It is a very common practice in this part of the country to see contractors put wood strapping over shingles to attach the new metal roof to. Some put a vapor barrier, others don't, this one didn't. As far as the existing roof goes I haven't opened the metal up to look but I'm told they changed the roof pitch when the addition was installed. I expect they just put up new rafters,laying the tops on the shingles and raising the eaves to get a flatter pitch. This being the case there would be no strapping to spray between. You should be able to spray a solid blanket of foam onto the shingles. I'm quite sure there is no solid deck under any of this metal. The open framed (addtion area) is finished with the V-match knotty pine so the underside of the metal is not accesible to spray against with out removing (and probably damaging)all the finished ceiling, thus my thought of removing the metal and fiberglass and spraying directly to the back side of the ceiling. Again thank you for your time. I've got all winter to figure out a solution. Any other ideas and viewpoints would be greatly appreciated. |
