Why It's a Bad Idea to Roof Over Existing Shingles

The cost of a new roof is exceptionally high, and some homeowners look for a reasonably priced solution. Some roofers offer to place a second layer of shingles instead of replacing your entire roof to save money and time.

There are a few advantages to installing a second layer of shingles in Pittsburgh, as well as many disadvantages. We walk you through the positives and negatives of this process.

Why Homeowners Opt to Roof Over Existing Shingles

There are a few reasons homeowners may consider a second layer of shingles overlaying an old roof. Some of these factors include cost savings, less disposal, and a shorter time to completion. A roof overlay should not be the answer to an already suffering roof.

Cost Savings

When you add a second layer of shingles to your existing layer, cost savings happen in a couple of areas. First, you don’t have the disposal costs and dump fees for ripping off the old shingles and disposing of them. Second, you don’t have as many labor fees as you don’t need to rip off the old shingles and clean them up.


Some people decide to add a second layer of shingles versus a new roof because of convenience. You will have less cleanup to do after the job is complete because there is no need to tear down the old roof. There is less risk of damaging your landscaping and less hazard from falling debris.


It takes less time to add a second layer of shingles to a roof rather than replacing your entire roof. As long as there aren’t current issues with the existing roof that need to be repaired first, installation of the new roof happens much faster.

Why It’s a Bad Idea to Roof Over Existing Shingles

However, there are slight advantages to adding a second layer of shingles to your roof. We’ll review all the reasons you shouldn’t consider a second layer of shingles on your Pittsburgh home. Many find the disadvantages far outweigh the small cost and time savings.

Voided Manufacturers Warranty

You will notice that most, if not all, roof shingle manufacturers will void the warranty for a second layer of shingles. Research the shingles you would like to use before purchasing, and read all the warranty information. Only invest in the cost of a new roof with a guarantee that it will work.

Roof Decking Can’t be Inspected

The roof decking is the foundation of the rest of the components that make your roof. An important part of the roofing process is to check the roof deck for weak or rotting spots. This ensures the roof deck can handle a new roof.

Structural issues to your home may arise if your deck needs to be stronger and repaired. You need to remove the original shingles to be able to inspect the decking underneath properly. Long-term health issues can also occur from molding and rotting of the decking.

Does Not Fix Ice Damming

If your roof is prone to ice dams, be aware that adding a second layer of shingles to your roof may not fix the issue. Ice damming occurs when the snow on the edges of your roof begins to melt and refreeze. When this freezes, it can freeze between the layers of shingles, causing leaks into your home. When you add a second layer of shingles, you are not addressing the underlying issues causing the ice dams.

Heat Absorption

Shingles become extremely hot in the sun because they consist primarily of asphalt. Imagine how hot the pavement gets in the sun; your roof will get just as hot. Additionally, when you have two shingles layers, it doubles the heat absorption your home takes.

This additional heat layer will rot the shingles faster than if it were one layer on the roof deck. Because of this, you will oftentimes see a reduced lifespan of 40% of your new roof. Last, consider the increased energy costs of keeping your home cool in the hot summer.

Additional Weight

Your roof weighs a considerable amount, and asphalt shingles weigh between 275 and 475 pounds for every 100 square feet. Imagine adding a second layer of shingles to the first layer. This makes for a lot of additional weight.

Wintertime, for most in Pittsburgh, can also add snow and ice to the mix. Too much additional weight mixed with an unstable roof deck can lead to a structural collapse.

Trapped Moisture

Any moisture that gets between the two layers of roofing can cause long-term issues with the roof deck, insulation, and sometimes the shingles. The long-term issue with trapped moisture is that it will expedite the rotting of the roof deck. This will then send leaks into the attic area, further deteriorating the roof trusses.

Roof and Shingle Repairs Still Necessary

An issue with adding a second layer of shingles to the first is that the original problems with the roof had to be fixed. Roofs need to be replaced at the end of their lifespan. Oftentimes for asphalt roofs, you can expect to get about 20 years of life.

Roof vents, pipe boots, and flashing still need to be replaced, even if you are adding a second layer of shingles. If you forego replacing these pieces, you are sure to leak.

If you consider a second layer of shingles, you must repair damaged shingles before laying a second layer. This is where extensive repairs can get costly. Roof replacement is often only slightly more expensive than fixing damage and adding a second layer of shingles.

Curb Appeal

If you think adding a second layer of shingles will hide flaws in your existing roof, you may be mistaken. Shingles sit and seal against a flat surface. Asphalt shingles tend to take on the shape of whatever is under them. If the original shingles had inconsistencies, the new shingles would take on these deformities as well.

Another issue to consider is poor adhesions to the current layer of shingles. With poor adhesion, you may find peeling, curling, or slipping of the new shingle layer.

Home Resale Value

Adding a second layer of shingles to your roof could affect your home’s resale value. Insurance companies consider a second layer of shingles a liability to insure and often do not cover it. This becomes an issue when you try to sell your house because new prospective homebuyers will need help to insure the home.

Is Roofing Over Existing Shingles a Good Idea?

Adding a second layer of shingles to your Pittsburgh home may seem like a good idea at first. However, it can end up costing you more in the long run. Schultheis Brothers will always replace the roof to heed issues before they arise. Call our roofing experts today to schedule an estimate for your new roof.