If you currently have a single layer of asphalt shingles on your roof, one of your main decisions when it is time to install a new roof will be whether you should remove the old shingles before installing your new roof or whether you should have the new shingles installed directly over the old ones. When calculating the labor involved in installing a new roof, removing and disposing of old shingles can raise the cost of the project around $100–$150 per 100 square feet of roof, which can significantly increase the overall cost of your project. However, there are several reasons why you should pay the extra cost to have the previous shingles removed.
Potential Warping and Buckling of Old Shingles
Just because you cover up your old shingles does not mean that they go away. They continue to age as they did before your re-shingling project. As shingles age, they usually warp slightly. This curling and buckling can transfer up through your new shingles, causing your new roof to look older sooner and potentially compromising the effectiveness of your roof.
Additional Weight of Your Roof
Each roof is approved to hold a certain amount of weight. When you add a second layer of shingles to your roof, you drastically increase the overall weight of your roof. This can be a problem if you live in an area where there are large amounts of snow in the winter or leaves in the fall. Additionally, in the future, you may not be able to add patches over multiple layers of shingles, which can result in minor repairs costing you more.
Full Inspection of Your Decking and Underlayment
Perhaps the most important part of putting a new roof on your home is checking the current decking and underlayment. Depending on the insulation in your attic, your roofing contractor may be able to check your decking from your attic. However, for the most thorough inspection of your decking, you should remove the current layer of shingles. This will allow your contractor to see weak or rotten decking and replace it.
Additionally, placing a new layer of underlayment can help prevent leaks and condensation, which will extend the life of your roof. It will not be possible to add a newer layer of underlayment if you do not remove the current shingles.
Re-shingling May Void Your Materials Warranty
When you install a new roof, you will usually be covered by two warranties. One warranty will be from your contractor and will cover the manual installation of the materials. This warranty is usually for between 1-5 years, depending on your contractor. The second warranty will be for the materials for your roofing. This warranty is usually good for much longer, sometimes up to twenty years, depending on the quality of the materials that you purchase. However, if you choose to lay new shingles over old shingles, you may void your material warranty, which can end up costing you more to replace your roof later.
You May Trap Mold and Algae Between Layers
When you place new shingles directly over old shingles, your contractor will have to thoroughly clean the old shingles. However, it may not be possible to clean them completely, and mold, algae, or moisture may get trapped between the layers. This can grow and cause problems on both layers of shingles, decreasing the effectiveness and life of your roof.
While you may be tempted to place your new shingles directly over your old shingles, you should seriously consider removing old shingles first. If you want to save money, you can look into removing the old shingles or disposing of them on your own. For more information on your roofing options, check out websites like http://dsbahr.com.