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TOPIC: Roofing over existing roof

vented roof over old roof

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I could not find the answer that I am looking for out of the postes so here it goes. The house is a prefab Wisconsin home. One half of the roof has a vaulted celing and the other part has an attic. There is no venting for any of the roof which leads to a lot of ice build up. The first 2 feet of the roof from the eve up is metal. the metal holds the eve on to the house, if I take the metal off the eve would fall off of the house.(prefabs shipped with the eves folded on to the roof.) What I was thinking of doing is strip the shingels off of the house and leave the metal holding the eves on. lay 30# roofing felt down, then nail 2x4's or 1x4's on the roof verticaly.(I could nail also these to the eves to secure them better) re sheet the roof on top of the new strips and lay 30# felt on the new sheeting, then shingle. adding a ridge vent and mabey leaving a 1/2" space at the bottom between the facia and the new d edge for ventalation. My questions would be: how air space should I have? Should I put a foil backed ridgid foam insulation on top of the old roof or would this be a waste? How do I vent the end by the facia? Any help would be appreciated. thanks.
Dan Alder

4/10/2009
Here goes Dan. You could do it either way. Personally, I like to have a solid deck(sheathing). If your existing attic has no ventilation at all, then adding the rigid foam insulation would be beneficial on your heating and cooling costs. Any airspace for ventilation would help. I haven't ever seen any engineering studies that say you need a certain size gap with x amount of cfm flowing under the metal for adequate ventilation. [email protected]
Guest User

4/11/2009
The ICC calls for a minimum 1/2" vented airspace. I think 1/2" is bare minimum and it must be unobstructed. Todd Miller
Todd Miller
Isaiah Industries, Inc.

4/12/2009
Thanks Todd.
Guest User

4/12/2009