Should I Remove My First Layer of Shingles Before Reroofing?

Published: 04th May 2011
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When home or building owners are in the market for a new roof, one of the first questions they ask is "Do I need to tear off my old roof, or can I just roof over it?" It can be a difficult question to answer because while it is possible to roof over a single existing layer of shingles, it is always a better idea to tear the old shingles off and install a completely new roof.

Up until the year 2000, it was legal to install up to 3 layers of shingles on a single roof. However, Utah’s building codes changed, and now the building codes allow only two roofing layers on a single roof.

It is easily assumed that the more layers you have on a roof, the more protection you have, but that is not exactly true. It is always better to tear off the entire roof: the underlayment, the shingles, and the flashings.

Even if your current shingles are ideal for installing a second layer, the new shingles will not line up to your current shingles. It creates an apron, essentially preventing the new shingles from sealing well. This can result in shingles blowing off easily in lower winds. Also, if you look at the roof from the ground, it will be visible that the shingles do not line up.

You may choose that you would still like to roof over your existing shingles to save money. It costs about half the price to roof over existing shingles. However, there are several requirements your roof should meet to make this decision viable.

First, has your roof been leaking? Chances are that the underlayment (a waterproof material installed just under your shingles) is leaking. The underlayment is very important because it can keep water out even when your shingles don’t. If your roof is leaking, you should definitely tear off your existing roof and install a new one with the underlayment done correctly.

Another factor is the condition of your current shingles. Are they laying flat on your roof? If the shingles are curling or bumpy, it would be difficult for the new shingles to lay down properly and thereby the sealer strip (a strip of tar that seals the shingles down) will not hold the shingles together in windy conditions. When this happens, the shingles will be prone to blowing off in patches with moderate winds, year after year. This could result in the roof’s life being greatly diminished.

In the event you have two layers, it is important to avoid the temptation to take off the top layer and go over the bottom layer. Aside from the fact that this is against Utah's Uniform Building Code, you will not have a smooth surface to go over with the top layer. If you can imagine all the nails from the top layer that are left behind, you can envision the problems that occur when nails are pounded down, or pulled. Either way, the asphalt shingles in the bottom layer get pretty chewed up!

When a new roof is put on any structure, it is best to replace the flashings as well. Flashings help the shingles seal to the pipes, walls and other roof penetrations in areas that leak most often. During a re-roof it is common for the roofing contractor to seal to the old flashings. Sometimes, these old flashings are not as sound as new ones would be, and they tear off, causing problems for the building owner.

Simply put, the best option when reroofing, is to remove the first layer and start over. The pro's are:

- The roof deck (usually plywood or 1x slats) can be inspected for damaged wood that needs to be replaced for strength as well as giving the new roof system's nails plenty of holding power.
- You can make sure the underlayment is done correctly, giving the roof a longer life.
- The shingles will seal down correctly, allowing the sealer strip to hold the shingles together during winds up to 110 miles per hour.

Even if your roof meets all of these requirements, a tear off and re-roof will always have better and longer lasting results. What seems like a lot of extra money spent on a re-roof will actually end up saving you even more money in the long run. Brady Roofing is a Salt Lake City Roofing Contractor who will ensure your roof is installed correctly, resulting in less work for you as the building or home owner. Contact us today for a free estimate, or visit our website at www.bradyroofing.net for more information.


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