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Dear Roofing Experts, I am re-roofing a small house with standing seam galvalume, mill finish, and contacted several reputable roofers for estimates. Most of the quotes I have received have been for 26 ga. metal over a stripped and renailed roof, using a synthetic unerlayment. One, though has proposed 24 ga., leaving the existing shingles except where the decking needs to be replaced, adding 1 inch of expanded polystyrene, and then attaching the metal using 2 inch screws that penetrate the foam and the decking. I asked about using furring strips to create an air gap instead of the foam and they said that would risk condensation on the interior of the metal which would drip onto the roof and cause issues. Also, the house has a barrel dormer above the front door. Would it be possible and/or advisable to do this in metal? The same odd man out as mentioned above has suggested asphalt roll roofing for this section, while everyone else has said they could do it in metal. So my questions are: 1) Any reason to choose felt v synthetic underlayment? 2) Shingles - to remove or not? 3) Foam - is it valuable? About half of the attic is finished and does not appear to be well insulated; the rest is vented (but, of course, the vents could be shut and the whole thing could be insulated). 4) Assuming foam is used, I assume extruded polystyrene or polyisocynurate is better. None of them seem like very environmentally friendly materials, but is one better than others? 5) Mill finish, I know, loses some of its reflectivity as it gets a patina; how much, and is there anyway to improve the reflectivity of an older mill finish roof? Many thanks for your advice, and for the forums, which have been a great source of information.
Eric Novotny
An informed customer is the Best Customer!
ES, 1. Synthetic is preferable and not absolutely necessary but a benefit. 2. I always prefer to remove shingles and especially given you are in FL where the less thermal mass in the roof the better. 3. Foam would work but so would above deck venting. Condensation should not be an issue in FL and any moisture would drain out on the underlayment and out of the roof. 4. Poly-Iso has a greater R-Value per inch and is available with the foil facing (should face the underside of the roof but needs and air gap). 5. Keep it clean is the only thing you can do.

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