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Thread
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Topic: Insulating and Ventilating New Flat Roof and Mansard
Author: Joe Williams
Date Posted: 7/2/2003
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We are purchasing a two-unit, 80 year old building in which 3/4 of roof is flat and 1/4 is clay tile mansard. The new flat roof will be EDPM rubber and new mansard will be shingle. We have been told that in all likelihood there is no insulation in the roof. Is there a way to insulate the ceiling beneath the flat roof and mansard after the old roof is torn off? One option an insulation contractor mentioned to us was tearing off about a 5' wide portion of sheathing (exposing rafters) down the middle of the building, then blowing in insulation. Another potential option I read about here is adding a "deck over the existing deck" in the form of a fairly recently-developed product that has poly-isocyanurate insulation pre-attached to the new deck material with pacers in between. It forms a new "suspended deck" with poly-iso spacers to hold it up over the attached insulation. Could this product be used over the mansard as well?
My other question related to insulation is ventilation of the roof. Should any ridge vents be added to the mansard? There is soffit around the mansard. Should any soffit vents be added? Does the flat portion of the roof need to be ventilated in some way?
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