Insulation for Metal Roofing over Shingles

Guest User
3/30/2009
My partner and I just bought an existing, very remote, oyster farm with two cabins on it. One of the cabins has shingle roofing and leaks like a sieve, even though we put new shingles over the existing ones last year. This winter we had several storms with higher than normal winds (up to 75 kts) and a whle lot of rain (normal) with the lowest temperatures into the teens, but normally between 25 and 38 degrees. The cabin was unusable because it had so many leaks, possibly from the roofing nails, a flashing issue, or something else - we don't really know. Because the ceiling is made of hand-sawn yellow cedar, we don't want to ruin the aesthetics (or smell) of it by putting insulation on the inside. We are thinking of putting a 2x2 wood matrix over the existing shingles, nailed through to the rafters, filling the voids with 2" thick foam-board insulation and then putting metal roofing over it all. We will put an access / crawl ladder on the roof to reach the wood-stove pipes for cleaning and to reach the antennaes for the emergency radios. Does this sound like it would work, or do we need to strip the old shingles off and do something else in order to insulate and protect it from the heavy rains we get up here? Any thoughts would be appreciated. JBK
Todd Miller
Isaiah Industries, Inc.
4/5/2009
I would suggest working an airspace of minimum 1" running from soffit to ridge, vented, in the new assembly. Also, be sure that the roof you install is appropriate for an application of this nature.
Guest User
4/5/2009
Thanks for the reply. The idea of an airspace is good. We'll do it. What do you mean about the roof being appropriate for an application of this nature? Do you mean the type of meatl roof we will use, or the strenght of the roof, etc.? Also, is there a need to be concerned about leaving the old shigles in place (as long as the roof is strong enough to support it), as it will provide more insulation? The present shingles have some moss, which we can scrape away, and are wet, which will dry over time as we heat the cabin. Thanks again for the reply and any further information you can give. JBK
Todd Miller
Isaiah Industries, Inc.
4/5/2009
I would not worry about moisture in the existing roof -- it will dry out over time and not be a problem Make sure that the roof you install is approved for installation over battens rather than just over solid deck. Not all metal roof systems can be installed over battens. All best
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