San Antonio Roofing: Article About Adding A Second Layer Of Shingles
Homeowners will often ask San Antonio roofing professionals if it is possible to lay new shingles over old ones. The answer is yes. There are some circumstances where placing new roofing over old shingles may be a reasonable option. However, there are many instances when this practice should be avoided.
Adding a second layer of roofing material can only be done with asphalt shingles. It cannot be done with wood or with slate. Two roofing materials, such as asphalt and cedar shingles, should not be mixed together. In order to put new shingles on top of old ones, the first layer should be in relatively good condition.
What are some of the benefits of adding new shingles over old ones? Contrary to what is popularly believed, multiple layers of shingles do not increase the water resistance of a roof. In fact, this can actually cause more problems. The primary benefit of adding a second layer of shingles is to skip the labor intensive tear off process and save money on a roofing job. However, even this is only a temporary fix. It's cheaper to leave the old shingles on, but there is additional prep work needed in order to do a reroofing job. Extra work must be done when it comes to adding new flashings, fixing or replacing broken vents, and realigning misshapen shingles.
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Putting a second layer of shingles on a roof may reduce the cost of the roofing job by about $1,000. However, when the time comes to fix the roof again in about 10 years, the homeowner will need to pay to remove and dispose of two layers of roofing. While there are a few benefits of adding a second layer of shingles instead of doing a complete tear down, there are many reasons why doing so is a bad idea.
One reason is that shingles are made to be installed over a flat surface. They are not designed to bridge dips or gaps. Second, extra shingles add extra weight. Good quality shingles weigh between 350 to 400 pounds per 100 square feet. Most roofs are designed to support the load of one layer of shingles plus snow. Adding a second layer of shingles can lead to the roof decking sheathing or sagging between rafters or trusses.
Adding a second layer of shingles may save a few dollars at the outset, but in the long run, it will be more expensive. Homeowners who are considering this option should definitely consult a roofing professional to get their opinion.