Q&A - Layers of Roofing, How Many are Allowed On My Roof?

Is there such a thing as too many layers on my roof?

John asked, "My neighbor says I can put another roof over my existing roof that has two layers on it now. Is that true?"

It is advised you seek the local building department for an exact amount of layers that are acceptable. Every city and county vary with their own codes. Most steep-sloped roof products like tile, slate, metal and shakes only allow one layer. Asphalt shingles typically can have one more layer added over the top. For many years it was acceptable to put even the third layer. As roofers we look for this every this we do an estimate because it adds cost to the project. I’ve seen roof tear-offs that had multiple layers up to six.

Why recover versus a tear-off?

It is all about money. Some customers, and a few contractors, out there think they save lots of money doing an overlay but if you think about it there is prep time getting that old roof properly prepared to roof over. Any dry rot cannot be seen and becomes extremely costly repairing it later. Just selling the house and not caring about the future is a motivating reason to also do an overlay. The savings to me are just not worth leaving any roof on.

To answer your question John, The weight of the third roof is of concern. Since your house was designed for asphalt roofing materials, it probably has a load limitation of about 600 pounds per square (one square is 10 feet by 10 feet of area). With the weights of some asphalt shingles these days, some reaching near and some even over 400 pounds per square, a third roof could possibly do major damage to the roof structure and risk the life of anyone inside.

The best thing to do is to remove the two layers because the roof deck can now be inspected for dry rot and easily repaired being exposed. The new roof will now be installed nicely to the roof deck and definitely perform better than other options. KEEP THE WEIGHT OF AN ELEPHANT OFF YOUR ROOF.

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