Shingling Over Old Shingles: What’s Okay, What’s Not

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Asphalt shingles have been the most popular type of roof covering in North America for the past 150 years. Their popularity among homeowners stems from the fact that they are easy on the pocket, easy to install, easy to repair, and can last up to 50 years. Asphalt shingles are also a relatively energy-efficient roofing option and can be recycled to minimize landfill waste.

But while they are durable and long-wearing, asphalt shingles will eventually deteriorate. And once it’s time for a reroof, you’ll be faced with two options: tear-off or re-cover.

In a tear-off roof replacement, your roof will be stripped down to the wood decking and new layers of roofing material will be installed. In a re-cover (a.k.a. roof-over or overlay), your roofer installs shingles directly over the old material. For many homeowners, the latter is a good option because a tear-off costs a lot more and takes more time.

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But experts agree that a re-cover isn’t always the best solution. Below is a breakdown that should help you figure out which option will best suit your needs.

A roof-over is a good idea when…

  • Your home is relatively new.
  • Your old roof is up to code.
  • Your old shingles haven’t curled and are smooth enough to provide an even surface for the new layer of shingles.
  • Your roof’s supporting structures (e.g. beams and boards) are in good shape and can hold fasteners securely.

A roof-over is out of the question when…

  • Your roof sheathing is in poor shape. No-nos include large gaps between boards, water spots, ripples (a sign of delaminating plywood) and areas that feel spongy when walked upon.
  • Your existing shingles are rough, distorted or generally in bad shape.

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  • Your roof already has two layers of shingles. Most roofers strongly advise against going for a third because the deck may not be able to support the added weight. Tongue-and-groove sheathing may be strong enough to hold three layers of shingles, but other factors must also be taken into consideration.
  • You live in a hot and humid area. Multiple shingle layers may trap too much heat and cause your roof to “sweat”, which over time will result in a rippled, lasagna-like roof.

Is there a limit to shingle layering?

Layering works well for homes in areas that are prone to harsh weather conditions like hurricanes and snowstorms, provided the conditions listed above are met. As for limits to layering, most building codes allow up to two layers of organic or fiberglass asphalt shingles on roofs with pitches of 4:12 or lower. Roofs with steeper pitches are allowed up to three layers.

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The weight of the added material and the condition of the roof deck and old shingles will always be major considerations as well.

A Caveat

Some roofers consider re-covers to be little more than cosmetic procedures. They argue that while a roof-over may save you as much as 20% off the cost of a tear-off, it may cost you an additional 40% to 50% when the time comes for the roof to be replaced completely. However, take note that the situation will vary from one roof to the next, so discuss your options with a roofing contractor you can trust.

 

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Author Bio:

Dawn Smith is the owner and general manager of Peak Roofing Contractors. She’s been active in the Northern Virginia home improvement industry for more than a decade and is known among her colleagues and clients for her no-nonsense approach to roofing. Dawn carries on her family’s passion for home improvement both on and off the job and often writes about her roofing experiences and pro tips on the company blog.

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