Pros and cons of a new roof versus an overlay

Dear Angie: We need a new roof. A builder suggested overlaying over the existing layer of shingles. Is it wise to do this?  My concern is how would we know about any underlying damage?  I would appreciate any input about the pros and cons of this method.
– Kim T., Newton, Mass.

Dear Kim: In general, it is not good practice to overlay a traditional asphalt shingle roof versus a complete tear off and replacement for the very reason you stated: you can’t examine the decking to determine if there is any damage that needs repaired. If you don’t take your roof down to the sheathing, you will never know if you have proper underlayment, or are experiencing sheathing rot, or ice or water damage.

The best-case scenario for an overlay is sound decking; no previous or existing leaks; and a roof with no sidewalls where flashing is needed to tie in the roofing material to the exterior walls of the home. However, if you overlay, you cannot install an ice and water-leak barrier, as it has to adhere directly to the wood decking. So, if you have an ice dam in the wintertime, it could easily travel under the overlay and leak under the old roof.

The second layer is also more difficult to install properly compared to new shingles. Flashing around roof penetrations and sidewalls can be compromised. Plus, depending upon the size of your roof, you’ve added multiple tons of weight, which could pose a big problem if there is significant snow accumulation.

If there are any pros to overlaying a roof, it’s saving a little bit of money. But because of the amount of prep work involved in overlaying a roof properly, any savings are usually modest – maybe 25 percent – compared to a new roof. The shingles likely won’t last as long, so the job could actually end up costing you more in the long run. The savings simply don’t warrant the compromise of quality and potential risks.

That said, overlaying asphalt shingles with a metal roof could be an option, provided there is no underlying damage. Metal roofs offer energy savings but do cost more upfront than traditional asphalt shingles. They also last longer and stand up to foul weather better than shingles. No matter what type of roof you choose, make sure you tell your roofer to fix any underlying problems you have before installing any new roof.

The bottom line is your roof is arguably the most important component of your home. After all, it protects everything under it, so it’s not an area where you want to cut corners. When weighing the modest savings against the possible uneven appearance, reduced life expectancy, and risk of future leaks, I would advise against an overlay with new shingles. Find a quality roofing contractor who can assess your roof’s condition and do the job correctly.

Angie Hicks is the founder of Angie’s List, a provider of reviews you can trust on contractors, doctors, dentists and other service professionals. More than 1 million consumers across the U.S. use Angie’s List to help make tough hiring decisions easier.


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Comments

I have a 1949 1600 sf under roof with 8/12 pitches valleys and hips 2×6 rafters on 16" on center sheathed with 3/4 center matched lumber going over at least 1 layer of 3 tab shingles a partial tear took off the old tabs and left a nice wavy surface in pretty good shape. Over the top with shake faux architectural weaves over old valley cuts. The roof looks sharp. Being lifetime carpenter, I know the sheathing is good underneath in attic good and by using 1 1/4 tacks, I can feel the tecture of the wood when I drive the nails with my hatchet. Don't be fooled by all the hype about full tearoffs. Some codes require 3 and sometimes 4 layers of shingles on new houses. Roofs are designed to hold 40 to 60 pounds per square foot. 33 1/3 sf shingles weighs 90 pounds that's 3 pounds per sf------that's nothing for a house that weighs 80, 000 to 160, 000 pounds!!!

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