roof replacement

Old 12-10-08, 06:54 AM
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Join Date: May 2004
Location: cheverly, MD
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roof replacement

i am getting bids to replace my 20+ year old roof on a 45 year old house.

the existing roof is a single layer of shingles, looking in the attic, the roof itself is wooden slats (i think 1x6x12), no plywood. i cannot see any rot from inside the attic.

should l tell the roofing company to strip the old shingles, and install new? my understanding of local code is, it's OK for roofers to install new shingles over old if there is only a single layer.

are there any advantages or disadvantages to putting new shingles over old, beside to obvious savings on the add'l labor and landfill charges for disposing the old roof.

FYI..the existing shingles are in pretty bad shape, but only 1 small leak (patched)


Old 12-10-08, 07:50 AM
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As you state the obvious reason is to save money on removal and disposal.
The bad part is the look of the old shingles will telegraph through the new within a year or so. Imagine putting a paper roof over the old roof. While it is new and firm it looks smooth and slick. Then the paper gets wet and melts into the cracks and low spots. Now it no longer looks great. This is what happens with the new roof. Over time the heat molds the new roofing to the old.
One layer on a flat backing does not have any low spots to mold stays flat.
Plus if any damage happens to the 2 layer roof such as extreme wind or hail it takes twice as much work to repair it due to the 2 layers.
So there you have the pros and cons.
Oh and don't forget about the flashings. They are not going to tear off any shingles to check the flashings. They will only roof over them unless the flashings are obviously bad by seeing them. Double shingles will be double trouble at the flashing. Especially near chimneys. Usually involves lots or sealers.

Last edited by badeyeben; 12-10-08 at 07:55 AM. Reason: Part about flashings.

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