What are the pros & cons with putting a new roof shingle over an old one?

Question

It's probably cheaper to leave the old one on for labor cost sake. It's the first original layer that needs replacing. I heard you are not supposed to stack more than 3 layers....

any problems with additional weight or fire hazard or leaks?

Answer 1

Yes, it is definetely cheaper not ripping off the old roof. You save on the labor cost plus removal of the old layer. In my humble opinion, that is the ONLY advantage. The downside is secondary leaks. You are placing new tiles on top of old ones that can and will buckle or are missing areas. Also you are adding a lot more weight. If you are going to keep the home, it is far better to have the tear off done and keep just one layer up there.

Answer 2

1

Answer 3

The national building code requires you to have only 1 layer on the roof. Also you will void the warranty on the shingles if their 2 layers.

Answer 4

New Roof Over Old Roof

Answer 5

pros cons putting roof shingle

Answer 6

Some city my make you remove all layers befor putting on new shingles. Check your local codes first.

Answer 7

Your local building code will determine how many layers of shingles are allowed. One square (100 sq-ft) weighs between 190 to 240 lbs, so you are looking at about 2 to 2.5 lbs per sq foot of dead load.

Roofs are designed typically for 10 or 20 lbs of dead load, so 2 layers of shingles would not be a problem for a normal roof. Unless you have the original design specs showing your roof can support 3 layers, I would limit to only 2 layers max.

IMO, the greatest disadvantage of adding layers to a roof is that if you have any existing leaks - and you don't fix them before adding a new layer, you will probably still have leaks to deal with after the re-roof.

A tear-off will let you fully examine the quality & integrity of the underlayment (OSB or plywood), any plumbing vents, ridges, and other roof penetrations such as chimneys or vertical walls and their associated flashings. Then you can implement necessary repairs, add new flashing or valleys where needed and be assured of a water-tight roof.

Answer 8

Usually there is no problem with weight-u are allowed three layers before you must strip everything and start over. I do not know of any additional fire hazards.
The plus side>>>Two layers of shingles will insulate the inside of your attic area better from the heat. This is a factor in southwestern and southeastern states. It is highly recommended to use tar paper over the existing shingles. Using tar paper over old shingles will also help blend any irregularities from the new shingles being nailed over the old roof. Removing the old roof is a laborious task and will add approxiametly 25% to the bill so going over shingles with a new roof is cheaper.
The other side>>>>After you remove an old roof(a big job considering the work involved, cost of hauling off shingles(be sure to check with building officials who might know of recycling places that will take shingles) it is nice to see what is underneath. If there is any bad areas, they can be repaired and it might show up possible problem areas that might have otherwise been hidden. Nothing beats a clean fresh plywood deck, and new shingles. THE END RESULTS ARE MUCH NICER.

Answer 9

Well, it's two for and two against. I have to agree with Dr.SPhil, every roofer I've ever talked to, and I deal with them all the time, says that two layers of shingles is the most load any roof should carry safely. If you think that's not the case, try carrying a couple squares worth of shingles up a ladder onto a roof and see how heavy they are. If you want to put a new layer on over the first layer, then the first layer has to be in fairly decent shape, they shouldn't be all cracked and curled or the new layer won't seal nor will it look good.

Answer 10

If your roof does not leak, you can have up to 3 layers. If your roof does leak, man rip it, and start over. I have a 80 year old house a few years ago I tried a chepp way out, now I have a home equity lone!