Layering asphalt shingles over an existing roof is a good way to replace a roof quickly but is not always the best roofing
solution. While many contractors may encourage you to just add an additional layer to your roof, this suggestion can be a bad idea if your shingles are in bad condition or you have multiple layers of asphalt shingles already. Conversely, a roof that is relatively good condition can easily withstand asphalt shingle layering without any adverse affects.
The reason why many homeowners are drawn to the option of layering asphalt shingles over existing roofing is the reduced work, and therefore reduced cost, that is involved. If you plan on doing the roofing yourself, you can save yourself days worth of work by shingling this way. Of course just because you are shingling over an existing roof does not mean that you do not have to replace flashing and broken shingles before you begin.
The largest disadvantage to adding an additional layer of asphalt shingles over an existing roof is the added weight involved. Depending on the building code that governs your particular area, you may only be able to layer the roofing once. The next time you need to replace your roofing you would have to remove, or pay someone to remove, both layers. The building codes that allow layering of shingles often don’t have to worry about significant snow loads, so be sure to check your local codes. Keep in mind that the type of asphalt roofing that you have on your roof will affect the weight involved as well. Asphalt roofing that has a 30 year or 50 year warrantee may be significantly heavier than cheaper options and therefore less desirable when layering roofing.
If you determine that your roof can withstand the extra weight and the cost and time savings are worthwhile, you should determine if you are a good candidate to layer asphalt shingles over the existing roof. It is important if you are considering layering that the old roof is covered with asphalt shingles that are not bent, cupped, or warped and that there are no current leaks on the roof. Unexplained leaks will not necessarily be solved by layering asphalt shingles over the existing problem, and bent shingles will cause your new shingles to bend as well.
If you have either of these deterrents to layering, fix the problems before laying your new asphalt shingles. Leaks should be repaired and shingles can be removed and replaced before your new roof is installed. Keep in mind that many times leaks are the result of problems with the flashing, so carefully examine all areas of the roof to find any problems.
Before beginning you should also consider whether layering new asphalt shingles over your existing roof will void the warrantee of your new asphalt roofing. Some manufacturers will declare the warrantee invalid because layering new roofing over old shingles can affect the performance of the material. To avoid this hazard, call and ask about the manufacturer’s policy on layering. Then get something from the company in writing and put it in a safe place with your receipt just in case of any problems.
Layering roofing is a decision that should carefully be considered before any work is done. Talk it over with your contractor and be sure to do research on your own before attempting this. Keep in mind that if you are still in the house when you must replace the roofing again the cost will be greater to remove the extra layers, making current savings much less.