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Can You Put Three Layers of Asphalt Shingles on a Roof?

December 6th, 2021 | 6 min. read

Can You Put Three Layers of Asphalt Shingles on a Roof?

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A roof replacement is a big investment. Because it’s such a big investment, some homeowners try to save money where they can. 

One of the ways they do this is by nailing over their current asphalt shingle roof. But sometimes, there are already two layers of shingles on their current roof. 

That’s when we’re asked, “Can’t you just put a third layer of shingles on my roof?” The answer to this question is actually quite simple.

For over 30 years, the team at Bill Ragan Roofing has helped homeowners understand all aspects of the roofing industry and the “why” behind certain rules and laws. Even when it’s something as simple as the number of shingle layers you’re allowed to have on a roof. 

To start this article, we’ll get right to the point of if it’s possible to put three layers of asphalt shingles on your roof. After getting that answer, we give you the 4 warnings you and other homeowners need to know about nailing over your old roof. s

Can you put three layers of asphalt shingles on a roof?

No, you can’t put three layers of asphalt shingles on a roof. In most states, you’re only allowed to have two layers of asphalt shingles on a roof for fire safety reasons. 

can you put three layers of asphalt shingles on a roof

But that doesn't mean you won’t still see roofs with three or four layers today. And some roofing contractors will still install more than two layers.

However, a reputable roofing contractor will recommend a full replacement if you already have two or more layers. Now, if your current roof only has one layer of shingles, it is possible to do a nail-over reroof if the situation is right.

Just be aware, most roofs won’t be a good candidate for a nail-over. If your asphalt shingle roof is near the end of its lifespan and the shingles are flat (no lifted or cracked shingles, blisters, or bumps), your roof might be a good candidate for a nail-over. 

The roof also must have only a few penetrations, a small amount of flashing, and no walls that butt up against the shingles. However, it’s ultimately up to what your contractor finds during your roof inspection that determines if a nail-over is an option.  

4 warnings about nailing over your old asphalt shingles

Now you know your roof is only allowed to have two layers of asphalt shingles. Remember, if you have more than two, you’ll have to replace your roof.

But if you only have one layer and want to try to save money, a nail-over might be a possibility. Before you try that though, there are some things you need to know about nailing over your old shingles. 

1. Your roof decking can’t be inspected

Roof decking (also known as roof sheathing) is the foundation of your entire asphalt shingle roof system. Unfortunately, there’s no opportunity to inspect the decking when nailing over your old shingles. 

rotten roof decking(Rotten decking)

If there is a problem with the decking and one of the boards breaks during installation, the contractor will take off the old shingles, replace the decking, put the old shingles back on, and start installing again. This adds to the time it takes to replace your roof and even adds to the final cost of the job. 

Unlike nailing over, your roof is taken down to a clean decking when getting a full roof replacement. This means your contractor has a chance to inspect the decking’s integrity to see if it can handle your new roof. 

And if they do find problems with your roof decking, the boards will be replaced before installing your new roofing components. 

2. Your current roof flashing has to be used

Roof flashing is metal material placed anywhere the shingles butt up against something, such as a wall, chimney, or in open valleys. It's one of the most crucial roofing components that every roof needs to have. 

roof flashing around chimney(Flashing on chimney)

If you get a nail-over, your current contractor must rely on the flashing already on your roof from the last time it was replaced. If the metal’s integrity is compromised or the flashing job was done poorly, you should not get a nail-over. 

If they use the compromised flashing during your nail-over, it’s guaranteed you’ll have leaks. If you’re seriously considering a nail-over, ask your roofing contractor about the condition of your roof flashing before agreeing to any work.

3. Your new asphalt shingle roof won’t qualify for the best warranties

All asphalt shingles come out of the package with a material warranty from the manufacturer. For example, 3-tab asphalt shingles come out of the package with a 25-year warranty. 

On the other hand, architectural asphalt shingles have a 30-year warranty that’s prorated after 10 years (coverage diminishes over time). But when you use all the roofing components from one manufacturer for your roof replacement, you can get the 50-year non-prorated enhanced warranty.

Because a nail-over doesn’t replace certain crucial roofing components, you won’t qualify for the enhanced warranty. Even if you get architectural shingles for your nail-over, it won’t be possible to get the enhanced warranty. 

Your contractor’s workmanship warranty will still be the same, but you’ll only have the out-of-the-package material warranty on your asphalt shingles. 

4. Upgrading a 3-tab shingle to an architectural shingles creates an aesthetic issue

Before a roof replacement, you’ll need to consider if you want to keep your current asphalt shingle or if you want to upgrade. Most homeowners who have a 3-tab asphalt shingle roof want to upgrade to architectural shingles.

But when you upgrade and nail over a 3-tab shingle with an architectural shingle, it causes an aesthetic issue. This is because 3-tab asphalt shingles run on a 5-inch exposure (you see 5 inches of the shingle out of the full 12 inches) while architectural shingles run on 5 ⅝ inch exposure. 

This difference in size creates a hump on your roof every 8 shingles. That’s why I recommend nailing over with the same asphalt shingle you already have on your current roof. 

Is it worth it to nail-over instead of replacing your old roof?

Now you know the 4 warnings of nailing over your old asphalt shingle roof. But remember, it’s up to what your roofing contractor finds during their inspection if your roof isn’t a good candidate for a nail-over.  

But what if nailing over is an option for you? Is it really worth it to save money instead of just replacing it altogether?

To answer this question, you need to know how a nail-over and roof replacement truly match up. That’s why we wrote another article comparing a nail-over to a full roof replacement on key factors like lifespan, cost, and more. 

The team at Bill Ragan Roofing has provided homeowners in Nashville and surrounding areas with high-quality roofing services since 1990. We work with you and your budget to ensure you get a roof that lasts for decades. 

Check out Nail-Over vs. Roof Replacement to help you decide which one is right for you and your upcoming roofing project.

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