Home » Blog » Roofing » Can you roof over existing shingles?

Sometimes we’re called out to quote a residential Colorado roofing service and we find that someone has roofed over existing shingles. That is, they’ve added new shingles over old, damaged or worn-out ones. Often when we see this, it was the homeowner that installed new shingles over the old ones, and not a roofing company. Most roofing companies know not to do this.

In this post, I thought I’d share why you shouldn’t roof over existing shingles.

two layers of roofing shingles

older green roofing shingles underneath newer, white shingles

Weight

Asphalt shingles are heavy. A bundle weighs between 50 and 80 pounds. The roofing deck (that’s the wooden structure below the singles) wasn’t designed to support the weight of two layers of roofing shingles. When you install a second layer of roofing shingles, you’re compromising the stability and integrity of your home or structure.

Lay Flat

Shingles are designed to be installed onto a flat, solid surface, such as your roofing deck, not a flexible, wavy surface such as another layer of roofing shingles. Each shingle depends upon a flat surface to function properly. When you install roofing shingles onto an existing layer of shingles, that existing layer is not flat or solid.

Security

Roofing shingles are installed by first nailing one row to the roofing deck, then another row covering approximately 2/3 of the first row, then a third row covering 2/3 of the second row, and so on. The nails securing the second row of shingles actually go through the second row and the first row of shingles. If you install new shingles over existing shingles, your nails will need to go through two new shingles, plus the two old shingles, so four shingles total. Normal roofing nails aren’t long enough to go through four layers of shingles. As a result, your roof won’t be as solid or secure.

The cover-up

What if there’s an unseen problem with the first layer of shingles, such as a leak? If you just roof over the problem, you’re not fixing the leak – you’re just covering it up. What’s more, if there’s the slightest bit of mold or algae on the first layer, and you add another layer of shingles on top of that, that mold or algae will spread due to the warm, humid environment you just created for it, and you just shortened the life of your new shingles.

Inspection

When you go to sell your house, the inspector will notice two layers of shingles, and they won’t like it. Neither will the new buyers. You will have to tear it all off and start over. You may as well do it right the first time. If you are local, call our Colorado roofing company and we will provide these services the correct way.

Summary

If you’re reroofing yourself, you might be thinking it’ll save you some time now by leaving the old shingles down and install new ones right over top. This will only cause problems later. Do the job right the first time and remove those old, worn-out, or damaged shingles before you install new ones.

If you are nearby and are in need of Colorado roofing services, contact us now! We install and repair roofs in Greeley, Loveland, Fort Collins, Denver, and surrounding areas.

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