A roof overlay is when a new layer of shingles is installed directly over the existing old roof, without tearing the old shingles off first. It is faster and cheaper than a full tear-off because it skips the removal and disposal work. The tradeoff is real: an overlay hides any rot or damage in the decking, adds weight to the roof, traps heat, and usually does not last as long. Most building codes also limit a roof to no more than two layers.
An overlay, sometimes called a re-roof, is the shortcut version of a roof replacement. Instead of stripping the old shingles, a crew nails a fresh layer right on top.
Because it skips the labor-intensive tear-off and the disposal fees, it is the cheaper, faster option, and that lower price is what makes it tempting on a tight budget.
The problem is everything the overlay hides and adds. Nailing new shingles over the old ones means no one inspects the decking underneath, so any soft, rotted, or water-damaged wood stays buried and keeps deteriorating.
The second layer also adds significant weight to the structure and traps heat against both layers of shingle, which can shorten the life of the new roof. Building codes generally cap a roof at two layers total, so an overlay also uses up the home's only remaining option before a mandatory full tear-off later.
For a homeowner, an overlay can look like a smart saving and turn into a costly shortcut. The money saved up front is often spent later when the next replacement requires tearing off two layers at once and dealing with decking problems that were sealed in and left to rot.
In most situations a full tear-off is the sounder long-term choice, even though it costs more today.
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