Reroofing over asphalt shingles
Bought my house 27 years ago in Seattle, where it rains all winter but is sunny most of the summer. Did complete tear off then, installed new 3/8″ plywood over original 1×6 skip sheathing, new roofing felt, new 3 tab shingles. Shingles are showing their age from UV exposure, so time for a new layer, which would be the second layer.
Yes, another tear off would be the absolute best. But there have never been any leaks, there are no missing or curling shingles, 6:12 slope drains well, metal flashing and drip edges all in good condition. So this particular roof seems like a good candidate for a reroof without tear off.
The only concern I have heard is that the first layer will “act like a sponge” if not removed. Is that really true?
Bicycle George
Replies
Here are some suggestions keep in mind while installing second layer of roof:
A.A second layer is more difficult to install properly. I won’t speak to a haphazardly done job. You will get what you pay for with that. Doing a second layer right means a lot of prep work goes into the overlay anyway, and flashing (which, remember, is the most vulnerable point on your roof) is harder to guarantee. The savings you’re going to see may be in the range of a modest 25%.
B.That second layer of shingles won’t last as long. That in itself eats away at the savings.
C.You could be adding weight to your roof with a second layer that your house cannot handle. This is especially true if there is huge snowfall.
To install new roof following points kept in mind:
1.To start installing shingles, line up aluminum drip edge flush with the edge of the roof and make a pencil line at the top on each end of the house.
2.Using the chalk line, snap a line between the two marks to get a straight edge.
3.Pull the drip edge down about a half-inch from that line to create a gap between the drip edge and the fascia board.
4.Nail the drip edge in place using 1¼-inch galvanized roofing nails and a hammer.
5.Repeat steps for gabled ends, installing the drip edge up the roof along the gable.
6.Lay out 30-lb. asphalt roofing felt paper and nail it in place using 1¼-inch galvanized roofing nails.
7.To lay out the design for the shingles, begin at the bottom of the roof and place a tape measure ½ inch from the edge of the roof to ensure the shingles overhang the drip edge.
8.Mark 12 inches up on the roof for the first course of shingles, then mark every 5 inches all the way up the roof to set your reveal. Do this on both sides of the roof.
9.Using the chalk line, snap a straight line on each 5-inch increment.
10.Use the chalk line to snap a straight line vertically every 6 inches.
11.Install a starter course by cutting off the three tabs on a shingle, leaving only the top tar section.
I agree with Mark. Doing an overlay is the cheap way to go and you get exactly that a cheap rook that will not look as good or last as long. If money is the issue, given the current roof isn't leaking wait a couple of years save additional money and then do it right.
Bing
Thx for all the advice. Original question was: does first layer act like a sponge? New question: why wouldn’t second layer last as long as first assuming equal UV exposure?
I'd like to see the science behind the reasoning that a second layer won't last as long as the first, if the first has good integrity. Heat retention? Maybe, but the failure modes are driven more by UV than anything else. Truth or myth?
Not a roofer by trade, but have done quite a few.
My guess is that the issue is more to do with the uneven surface promoting cracks in the new layer. The shingles that fail first on an asphalt roof are often the ones that are curved at intersections or over the ridge.