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How Many Layers of Shingles Can Be on a Roof?

September 10th, 2021 | 5 min. read

How Many Layers of Shingles Can Be on a Roof?

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If you’re on a tight budget, you’ve probably already learned you can nail over your old asphalt roof instead of fully replacing it. However, this won’t be an option for most homeowners because of a few reasons. 

One of these reasons has to do with how many layers your asphalt roof already has. That begs the question, how many layers of shingles can be on a roof?

Here at Bill Ragan Roofing, our goal is to provide you with all the information you need to know to make the right decisions. That’s why we’ll be breaking down how many layers of shingles can be on your roof. 

After that, we’ll also give you the crucial information you need to know about nailing over your current asphalt roof. 

How many layers of shingles can be on a roof?

In most states, you’re only allowed to have 2 layers of shingles on a roof for fire safety reasons. However, you’ll still see roofs that have 3 or 4 layers today. 

2 layers of asphalt shingles

If you already have 2 or more layers, a contractor will recommend a full replacement. But if you're on a tight budget and the current roof has one layer of shingles, it is possible to do a nail-over reroof if the situation is right.

Most roofs won’t be a good candidate for a nail-over. To do a nail-over, an asphalt roof has to be near the end of its lifespan, and the shingles need to be lying down pretty flat (no lifted or cracked shingles, blisters, or bumps). 

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

4 things to know about nailing over your current asphalt roof

Now that you know that you’re only allowed to have 2 layers of asphalt shingles and that it’s possible to nail over your old roof. Yes, nailing over your old roof will be cheaper than getting a complete roof replacement

But if your current asphalt roof is a good candidate for a nail-over reroof, there are some things you need to be aware of before jumping right into your project. 

1. Your roofing contractor can’t inspect your roof decking

Roof decking (also known as roof sheathing) is the foundation of your entire roof system. When nailing over your old shingles, there’s no opportunity to inspect the decking before installing your new roof. 

rotten roof decking (roof sheathing)

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 can even add to the final cost of the job. 

On the other hand, your roof is taken down to its decking when getting a full roof replacement. This gives your contractor a chance to inspect the decking’s integrity to see if it can handle your new roof. 

If they find any problems with your decking, they’ll replace it before installing your new roofing components. 

2. The roofing contractor has to use your current roof flashing

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

When you get a nail-over, your current contractor must rely on the flashing already on your roof and the past contractor’s workmanship. If the metal’s integrity is compromised or the work was done poorly, you should not get a nail-over. 

If they use the compromised flashing during your nail-over, you will have leaks. This leads to spending even more of your hard-earned money on repairs and replacing the flashing. 

If you’re considering a nail-over, ask your roofing contractor if they saw any problems with your roof flashing. 

3. Upgrading 3-tab shingles to architectural shingles creates a lumpy roof

When getting a new roof in general, you need to consider if you want to keep your current type of shingle or if you want to upgrade. Most homeowners who have 3-tab shingles want to upgrade to architectural (also known as dimensional) shingles.

But if you want to upgrade your 3-tab shingle to an architectural shingle when nailing over, it causes an aesthetic issue. The issue happens 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 size difference creates a hump on your roof every 8 shingles. If you’re considering a nail-over, I recommend going over it with the same asphalt shingle you already have. 

4. Your roof won’t qualify for the best material warranty

Not only will upgrading your shingles lead to a lumpy roof, but you also won’t have the opportunity to get the enhanced warranty when nailing over your old roof. All asphalt shingles come out of the package with a material warranty from the manufacturer. 

3-tab asphalt shingles come out of the package with a 25-year warranty from the manufacturer. 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. Even if you get architectural shingles for your nail-over, you won’t be able to get the enhanced warranty. 

Your contractor’s workmanship warranty will still be the same, but you’ll only have the standard material warranty on your architectural shingles. 

Is a nail-over or a roof replacement right for you?

Now you know 4 things to know about nailing over your old shingles. If your roof isn’t a good candidate for a nail-over, you’ll have to get a full roof replacement

But if nailing over is an option for you, you need to know how a nail-over and roof replacement compare to each other to ensure you make the right decision. That’s why we wrote another article comparing nailing over vs. replacing 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. When getting a roof replacement with us, you can count on workmanship to give you a roof that lasts for decades. To back up that statement, we provide you with a lifetime warranty.

To ensure you make the right decision, check out Nail-Over vs. Roof Replacement to help you decide which one is right for you.

roofing material quiz

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