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Single Layer Asphalt Roof

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September 22, 2025 at 9:09 a.m.

HannahFord7

Ann from California asks: I have a single layer asphalt roof on my house. It is 30+ years old but does not leak. I am going to reroof soon. Should I put felt down first or just reshingle?

September 22, 2025 at 9:10 a.m.

HannahFord7

Below is what our roofing expert John Kenney with Cotney Consulting Group had to say in response to your question:

Ann, you're doing the right thing by asking before diving into a reroof, especially with a roof that's over 30 years old. If you're planning a full tear-off, you want to install felt or synthetic underlayment before the new shingles go on. That layer provides a secondary moisture barrier, protects the deck during installation, and improves the shingle layout for long-term performance. It's a standard part of doing the job right.

Now, if you’re considering a roof-over (adding a second layer of shingles without removing the old ones), that does change things. Underlayment isn’t installed between layers; the new shingles go directly over the old ones. While this may be allowed by code in some areas, it can shorten the new roof's lifespan due to trapped heat and limited ventilation. It also masks hidden deck damage, something you won't know until it's too late. The original roof needs to be flat, dry, and solid for a second layer to perform even reasonably well.

If you’re investing in a roof you want to last, a tear-off with new underlayment gives you a fresh start and peace of mind. It's a better long-term solution, especially on a roof at this age. However, a roof-over can work if cost is a significant factor and the existing shingles are in good structural shape. Understand what you're trading off.

September 22, 2025 at 9:25 a.m.

alextolle

Below is what our roofing expert Jose Castellanos with Bumble Roofing had to say in response to your question:

We highly recommend a complete reroof which includes removing the existing layer of shingles, installing new synthetic underlayment (not felt), and installing new shingles on solid sheathing. I always advise against overlays (installing another layer of shingles on top of the existing shingles) for a few reasons. The first reason is that no manufacturer will warranty the material. The second reason is that an overlay is simply a band-aid and may not address underlying issues such as water damage, dry rot on plywood, or ventilation concerns.

October 6, 2025 at 2:48 p.m.

alextolle

Below is what our roofing expert Henry Staggs with The Arizona Roofer had to say in response to your question:

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