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I'm preparing to re-roof my home. The current roof is shingled and I have recently repaired a few leaking spots. I've taken a look at a few options and I have a few concerns regarding code and longevity. This home is located in Northern Florida with a 1.7 to 12 roof pitch and a small 24" tall attic, the existing shingles have plywood decking underneath.

I do not want to spend extra, do unnecessary improvements or add additional load (weight) to the existing roof.

Can I place the new metal directly on the existing shingles? I have been told and seen it done and I am concerned if I should use a water/vapor barrier. I would like to NOT install furring strips and/or Styrofoam. I have concerns regarding the noise from rain and I am trying to understand/evaluate the costs respectively.

  • Voting to close as opinion-based. There's no objective way to answer this question. It comes down to risk tolerance and quality standards. – isherwood Apr 17 '17 at 14:46
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    There is a legitimate factual question as to the advisability of putting a metal roof over (asphalt?) shingles. I assume that there is plywood decking under the shingles. – Jim Stewart Apr 17 '17 at 14:56
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    It's fairly apparent that the OP is looking for justification to ignore best practice advice and proven techniques to save time and/or money. That can't really be given objectively, in my opinion. – isherwood Apr 17 '17 at 15:39
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Best practice is to remove the shingles and repair the deck as needed; I don't think anyone would consider leaving the shingles as more than "something you might get away with" - certainly not a best practice.

From my "old-school" perspective, red rosin paper (moisture, not vapor, barrier, and not as slippery as tyvek, etc) and those furring strips you don't want, then metal. Depending on the current level of roof insulation, possibly also that foam you don't want.

If you have major concerns about rain noise, new shingles or a rubber roof (EPDM, white side up in your climate) might make more sense than metal.

  • Thank you for your prompt reply. If I would remove the shingles, why would I want the furring strips and the foam? I'd like to be able to walk on it for maintenance and it would seem that I'm either walking on the furring strips or bending the metal. – Jeffrey Michael Apr 17 '17 at 16:40
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It CAN be done. However, I agree with Ecnewal that it's best to remove the shingles, of course, but it can be done with some precautions: 1) Low slope application, 2) Perimeter treatment, fireplace and skylight flashings, 3) Warranty, 4) High wind installation, and 5) appearance.

1) Because your roof has a slope of less than 2:12, you'll need to install a double layer of "moisture barrier" not a "vapor barrier", but follow the roofing manufacturers recommendation. They may require a "peel and stick" , in which case it will be difficult to install over shingles. (Do not rely on the shingles for your moisture barrier. Install as if on the roof sheathing.)

2) Eave and rack flashing will need extra attention because they will be installed over shingles (and presumably on existing flashing.) Also, verify you have sufficient depth around fireplaces, skylights, etc. to add the metal roofing.

3) You COULD void the warranty installing the Metal roof over the shingles. Verify with your installer that the installation is warranted and that you want a WRITTEN 30 year (min.) warranty at the conclusion. (By the way, metal shingles may be cheaper than the standard standing seam metal roof, although the slope may be too low. ) Also, you only want a CONCEALED fastener standing seam type installation.

4) Make sure the fasteners are extra long to penetrate the extra thickness.

5) If the shingles are not perfectly level, then the metal roofing will have bumps in it too. With shingles, it's not so apparent, but metal will show.

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