Can a Roof Have Two layers of Shingles?
Yes, a roof can have two layers of shingles. However, when adding a second layer or buying a home with two layers of shingles, there are drawbacks to consider.
How Many Layers of Shingles Can a Roof Have?
Most local building codes and regulations limit you to two layers of shingles. For example, the 2021 IRC (International Residential Code) states:
R908.3.1.1 Roof recover is not allowed.
A roof recover shall not be permitted where any of the following conditions occur:
1. Where the existing roof or roof covering is water soaked or has deteriorated to the point that the existing roof or roof covering is inadequate as a base for additional roofing.
2. Where the existing roof covering is slate, clay, cement, or asbestos-cement tile.
3. Where the existing roof has two or more applications of any roof covering.
Basically, building codes allow a second layer of shingles if the existing shingles and roof decking are in good shape. Plus, you can’t install additional layers over slate, clay, cement, or asbestos-cement tile.
In addition, most shingle manufacturers also allow a double layer of shingles. For example, GAF, one of the largest roofing manufacturers in North America, gives its blessing for two layers of shingles.
Their guidance is similar to the building code. Specifically, the existing layer should be flat and defect free. However, they do not recommend a second layer over certain types of roofing.
GAF asphalt shingles should not be installed over:
- Wood shakes
- Tile roofs
- Metal roof
- Asbestos shingles
- Roll roofing
- Low-slope membrane roofs
- Insulation (direct application)
- Decks other than wood unless an approved specialty deck
What Does Two Layers of Shingles Look Like?
Many homeowners and home inspectors often mistake a single layer of roofing for two layers. This is because the edge of a roof typically has underlayment, an ice and water shield, starter shingles, and then the shingles.
When checking for multiple layers of shingles, lift one shingle at the eaves of your roof. If there is an older layer of shingles underneath (not a starter strip), then you have two layers of shingles.
Benefits of Two Layers of Shingles
The number one benefit of a second layer of shingles is saving money on your new roof. Labor costs are the most expensive part of new roof installation. So, you can save several hundred dollars on the labor of removing the old shingles. Plus, you’ll save on disposal fees.
However, some roofers may charge more for a “roof over.” This is because some roof shapes and designs make a “roof over” more complex and time-consuming.
Cons of Two Layers of Shingles
There are many cons to adding an extra layer of shingles that quickly negate any cost savings.
The most significant drawback of a “roof over” is the reduced life of the new shingles. Although there are no definitive numbers, most roofing professionals see 30-year roofs fail 5-10 years sooner.
With two layers of shingles, heat gets trapped between the top layer and the old layer. This extra heat accelerates the decomposition.
According to dumpsters.com typical 1200-square-foot roof with 3-tab shingles weighs about 1.5 tons. Whereas 1200 square feet of architectural shingles weigh about 2.5 tons. Likewise, two layers of architectural shingles weigh about 5 tons. Although most modern roof structures can handle that much weight, older roofs may not.
Another significant problem with a roof overlay is the potential for hidden damage. Removing the existing layer of shingles allows roofers to evaluate the roof decking for serious damage. (Not all damage is visible from the attic side) For example, there may be water damage, rot, or mold growth under the shingles.
Expensive Roof Repairs
Roof repairs are typically more expensive when there are multiple layers of shingles. First, leaks are harder to trace. Since water has to make its way through two layers of shingles, underlayment, and roof sheathing, the leak may show up far away from the original entry point.
Second, it’s much harder to repair two layers of shingles. So, if you end up with roof leaks, expect to pay extra for repairs.
Although not a prominent issue, a second layer of roofing is often unsightly. A single layer of shingles over a flat surface creates an aesthetically pleasing roof line. However, with two layers, the ridges of the bottom layer transpose through the top layer.
Do Home Inspectors Count the Layers of Roofing
According to InterNACHI, the dominant professional association for home inspectors, home inspectors are not required to use ladders or walk on roofs. Consequently, a home inspector is not required to count the layers of shingles or report the number of layers in their inspection report.
However, many home inspectors do use ladders and walk on roofs. The best way to know if your inspector will count the roof layers is to ask them before you hire them.
Generally speaking, you should not hire a home inspector who does not make an effort to count the roof layers.
Will Home Insurance Cover Two Layers of Shingles?
Yes, most insurance companies will issue policies on homes with two layers of shingles. However, when we contacted insurance companies to inquire about this, the only insurance company that replied was Liberty Mutual.
However, it’s a good idea to read your policy and ask your insurance agent about specifics. Typically, only the top layer of shingles is covered. Plus, there may be an additional premium added to your policy.
You can install a new layer of shingles over an older roof. The benefit of this is saving money on your new roof. However, in the long run, you will lose money due to the reduced life of the roof.
There are many significant drawbacks, and your best option is opting for full roof replacement.