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In many cases, provided the existing shingles are in reasonably smooth condition and the decking below them is sound and provided you use an appropriate underlayment between the old shingles and new roofing, this can be done.
However, before proceeding, check with the metal roofing manufacturer to make sure that they are okay with this being done given the product design and metal thickness you choose.
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I talked to 2 contractors. One uses a framing over my shingle roof (1 layer only). The second one says he installs the metal directly over the shingles. No framing, insulation, etc. Is this safe? Some people have said that installing directly over shingles would cause the shingles to hold moisture and rot the roof decking. PLEASE HELP!
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If the installation is direct over the old shingles, I would suggest a layer of underlayment. This would usually be 30-pound felt, possibly with a slip sheet on top of it, or a layer of polymer based underlayment.
In any event, make certain that the installation method being used is approved by the manufacturer of the roofing material. This is critical!!!!
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In most cases, yes, you can install many metal roofs over your current shingles. This is often easier to do with shingle style modular or heavily corrugated products than it is with smoother standing seam profiles.
A slip sheet is a non-asphaltic product which would be installed over a standard roofing felt underlayment for the purpose of preventing the underlayment from sticking to the roofing.
There are, however, newer polyer underlayments which act both as the underlayment and the slip sheet. Product names for these are SharkSkin, RoofTopGuard, Titanium, and Tri-Flex.
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We live in a small cabin type home with at least three if not four layers of shingles on the roof and several are pretty rough looking. My husband being the tight budget minded person he is, is talking about putting a Tin roof over all these shingles to save money instead of having them removed. We have heard both ways 'leave on' and 'take off' ... he will not listen me so I'm asking experts (men) what do you think? Our roof guy will not say ... he is just going to get us two estimates ..one with shingles and one to remove shingles...HELP!
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The only legitimate "expert" to answer this question is a structural engineer (of either gender). And even then, a site visit would be important.
However, let me share a few thoughts.
If there is a building code in effect where the home is located, a special waiver will have to be obtained to allow installation over more than one layer of old shingles.
From a practical standpoint, the new metal roof may add less weight than the old layers of roofing have lost with worn-off granules and evaporated oils.
I have seen successful installations over multiple layers. However, the structure must be able to handle the weight load.
If there are any areas where the old roof is showing signs of excessive weight or where leaks have been abd there might be rotten wood, they must be addressed by removing the old roofing.
If you try to go over the old roofs, you must be installing a product which can be installed in this manner, per its manufacturer.
Shingle style and more heavily formed metal products will be more forgiving of going over an uneven surface.
I realize I am not giving you an answer but I do hope I am giving you some more criteria for making your final decision.
6/25/2003
Or copy this URL: https://www.metalroofing.com/spirit/comment/1930/find/Isaiah Industries, Inc.
6/26/2003
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Or copy this URL: https://www.metalroofing.com/spirit/comment/1932/find/Isaiah Industries, Inc.
10/4/2003
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Or copy this URL: https://www.metalroofing.com/spirit/comment/1934/find/Isaiah Industries, Inc.
10/9/2003
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Or copy this URL: https://www.metalroofing.com/spirit/comment/1936/find/Isaiah Industries, Inc.
10/19/2003
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