Layering Asphalt Shingles - Good Idea?

Lets make this simple

Lets make this simple. Roofing is expensive. So why not save a little money by adding one more layer of shingles on top of the old shingles? Double protection, right?

Wrong! There are many very important reasons why layering asphalt shingles is not a good idea.

1. Structure. Roofs are designed and built to carry a certain load (typically, one layer of asphalt shingles). Asphalt shingles are very heavy. Laminated architectural shingles weigh around 350 to 450 pounds per 100 square feet (one square). Once you start adding layer upon layer of asphalt shingles, you will dramatically increase the load bearing down on your roof decking. Imagine the weight of three layers of asphalt shingles and add on to that a good amount of wet snow. This can, and has, lead to catastrophic roof damage. If you drive through any old neighborhood having houses around the 100 year old range, you will find roofs with roof decking that is visibly bowed in toward the attic. This happens when multiple layers of shingles where installed on a roof. The roof decking simply cannot handle the extra weight.

2. Warranty. Shingle manufactures will not warranty their shingles if they are applied over old shingles. New shingles will not seal properly over old shingles. Shingles are manufactured with an adhesive that is engineered to glue itself to specific underlayment after being exposed to warm summer temperatures. Also, roofing material will fail quicker and have a reduced life if installed over less than ideal underlayment. Do not look to the manufacturer to stand by their product even if the material has a legitimate defect.

3. Existing Roof Problems. If your roof is leaking now, chances are that it will continue leaking even after another layer of shingles is added. Again, the adhesive on the shingles will not create a watertight seal. You also may have damaged roof decking. Damaged roof decking cannot be identified and properly repaired unless the old roofing material is removed prior to installing new shingles. Covering up damaged roof decking will only create bigger, more expensive problems in the future.

4. Cost. Save a little now, pay a lot later. If one were to add several layers of shingles on their roof, eventually there will be a time when all the layers will have to be removed. The older shingles are, the more difficult it is to remove them. The harder they are to remove, the more you will pay for labor. In my opinion, you are just postponing an eventuality. It will not only cost more to remove the shingles, it will also cost more to repair the damage caused by layering shingles. In most cases of layered shingles, expect to pay to replace the entire roof deck. This is not cheap by any means.

5. Building Code. Minimum building code, enforced by your local municipality, has been changing to help eliminate the problems and dangers caused by layering roofing shingles. Most municipalities in Wisconsin will no longer allow more than two layers of shingles on a roof. Please check with your local building inspector prior to adding layers of shingles to your roof.

When deciding on a new roof, take extreme caution if you are considering adding layers of asphalt shingles to your roof. More than likely, you will compound problems, create an unsafe weight load on your roof, and it will end up costing you more in the long run. My recommendation is that, under no circumstances, should have multiple layers of asphalt shingles.

by: Wisconsin Contractor

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