What is the difference between a tear-off and a layover?

Exteriors Roofing
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In roofing, a tear-off removes all layers of shingles and underlayment from a roofing system. A layover typically refers to adding a new layer of shingles over the existing shingles.

In our Chicago area, we almost always do a tear-off. While some municipalities allow by code a second layer, we do not recommend it. Here’s why: covering a roof that is presumably in bad shape (which is the single most common reason for a new roof), with new shingles hides potentially hidden defects in the roof deck such as rotted wood, or delaminated plywood. In fact, we had a roof project this week in Rolling Meadows IL that, when looking at the old roof, looked fine. But there were 19 sheets of plywood that needed to be replaced. The plies were separating, and was not safe.

Another reason to do a tear-off is to add an ice and water shield. Over the past couple of decades the roofing industry has changed, and the International Residential Code now requires an ice and water shield along the drip edge and other parts of the roof. Without stripping the old roof off, it is difficult to determine whether or not this was ever installed, or installed correctly according to current code.

We have had scenarios where someone fell through a rotted garage roof (yes he escaped with only minor injuries), because the “big box” retailer who installed the roof skimped out and didn’t even install felt paper. The roof appeared somewhat normal, and a little weathered, but when walked on, the plywood split, and gave way. I remember that day - what a way to enter a garage. The person’s feet were dangling over the hood of the Buick inside with a 2’ diameter hole above.

Further, adding a layer of shingles adds stress to the roof structure. It is not uncommon for the shingles to weigh 240 pounds for a 10’ x 10’ area, potentially adding tons of additional weight to a typical home. The roof rafters may or may not be designed to handle the load, and may bend/break with the extra weight.

Almost always, it’s not worth saving a few dollars on this one.

Your governing jurisdiction may also have rules about the permissibility of layover vs tear-off.

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We recommend you remove existing roof shingles to be able to inspect all plywood but state code allows a second layer of shingle.

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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.

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We always recommend a tear-off, but I know it is not always in the budget. If you do decide to do a layover, I recommend replacing the chimney, walls, pipe boots etc.

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Also if you are using a longer life shingle dimensional/architectural you will be much better served by tearing off the existing roof. If you recover a roof you are now baking it from both sides. The layer of asphalt shingles underneath get way hotter than a plywood deck. So now it is not only getting cooked from the direct sunlight but the new shingle is also taking extreme heat from the second layer on the bottom. So you are buying a longer life shingle that you are not likely to get the extra life from because by recovering the existing roof you just shortened that life cycle. Along with all the other potential problems you might be covering up with the plywood deck. If there are areas of bad or soft plywood and you nail the roof over it you are more likely to have shingles blow off in the future.

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Reroof not recommend Here’s why: cover old roof that is presumably in bad shape and install new shingles over bad roof with potentially hidden defects such as rotted wood, or plywood. In not safe.