Adding insulation to existing metal roof?

Guest User
1/31/2008
Hello- Hopefully someone here can help. A few years ago, I bought a 200-year old house that was in a serious fire back in the early 80's. Before the fire, the house had been two stories. After the fire, they only finished the downstairs and left the "attic" unfinished and un-insulated. As part of the renovation, the previous owner had metal roofing installed directly on 2x4 laff and 2x8 rafters. There is no sheathing, paper, plywood, etc. - just the bare metal attached to the laff and rafters. They insulated the ceiling of the first floor with R-19 fiberglass faced with craft paper. This is pitiful for how cold this climate gets. As a result, there is a considerable amount of condensation on the underside of the metal. When the weather is just right, the condensation gets so bad it drips off the roof. It's never been bad enough to do serious damage, but the attic is only used for storage and a little water hasn't been a problem. The attic has soffit vents and a very small ridge vent. There are several windows in the attic, I've tried leaving them partially open to aid in ventilation, but it doesn't seem to make a difference. We would like to renovate the attic into living space, but are concerned about the lack of insulation and the condensation problem. We live well out in the boonies, and can't find a local contractor who will touch this project. If we finish the attic, we will certainly need to add insulation. The problem we are facing is knowing how to deal with the condensation problem. We want to frame out the rooms on the second floor to 8' ceilings, which would leave several feet of space between the ceilings and the roof. Should we insulate directly on the new ceilings, and hope that we can add enough to prevent the transfer of hot moist air up to the roof? One contractor mentioned installing spray foam directly against the roof's underside - in addition to insulating on the ceiling of the new rooms. Is our problem really with ventilation, and not with lack of insulation? Another contractor mentioned installing power vent fans in each end of the roof to help draw air out, since the ridge vent seemed weak. Any thoughts or comments would be appreciated. This seemed like a straightforward project until we got such a mixed bag of responses when we asked contractors how to deal with insulation and ventilation to prevent condensation on the roof.
Todd Miller
Classic Products, Inc.
2/2/2008
Condensation occurs when warm, moist air hits a cool surface. Insulation and ventilation can both play roles in eliminating those conditions. That said, spraying the back of the roofing with closed cell polyurethane keeps moisture from reaching the back of the roof. It also insulates against the cold roof. It is one way to accomplish a good result without ventilation. A vapor barrier someplace between the living space and the roof is also helpful.
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