Stripping old shingles off a roof can be messy. Roofers have to toss the shingles down to a dumpster below, and even if they’re careful, they’re bound to get some shingle pieces on the ground. This has some homeowners wondering: can you re-roof over the existing shingles instead of doing a complete tear-off? The short answer is, “technically you could, but we strongly advise against it!” Here are some details to consider.
Roofing Over Existing Shingles
Many people wonder about this option because of the perceived benefits. They estimate that they could save labor costs if they skipped tearing off the shingles and just added another layer. Roofers typically spend the better part of a day stripping old shingles from the roof before putting the new roof on. If they didn’t remove the shingles, your roofing job would be quicker.
The roofers might also avoid having to rent a dumpster. This would lower costs since dumpster rentals are typically a few hundred dollars. Roofing over existing shingles also creates less mess. There would be less shingle debris and fewer nails in your yard after the project. But, for each of these perceived benefits, there are a host of other considerations that would advise against taking this route.
Cons of Roofing Over Existing Shingles
There are more downsides than there are upsides to roofing over old shingles. The primary one is the potential for problems with the roof deck to go unnoticed. If your old roof has been leaking for a while, the roof deck has probably been exposed to moisture. It may have some rotten, compromised areas which need to be replaced. But without stripping the old shingles off, the roofer won’t see and be able to replace the damaged roof decking. It will continue to lose structural integrity over the years and may cause your roof to start sagging. Even if you do not have visible leaking, it is impossible to see the structural integrity of the roof deck without stripping the old shingles. For that reason, many roofers, including Titan, will not even attempt adding an extra layer without taking the old ones off.
Another downside of adding an additional layer of shingles without tearing off the old ones is that all of the roof system components, like flashing, vents, soffits and fascia will remain largely uninspected. It is impossible to see what is going on under the surface of the shingle layer without tearing off the old shingles.
The extra weight of the additional layer of shingles is also a concern. It can put additional strain on the roof deck, which can lead to cracks and damage if the roof deck is already weakening. Small roofs, in particular, can’t always support the weight of two layers of shingles, making it structurally dangerous. Homes that are non-standard also run the risk of being structurally compromised due to the extra weight of a second layer of shingles. Asphalt shingles are much heavier than you’d think!
Many shingle warranties are voided if the shingles are installed over an existing layer. This does vary from manufacturer to manufacturer, however.
There are also building codes to consider. Some municipalities, in storm-prone areas especially, will not allow two layers of shingles on a roof. While you might think two layers are better than one, rooftops with multiple layers of shingles are actually at a greater risk for wind damage.
If you don’t know how your old roof was installed, there are additional concerns that come with re-roofing over the old shingles. If the old roof lacks an ice barrier or proper waterproof underlayment, roofing over it removes your chance to have these protections added. This means leaks due to ice damage will still be a concern, even with both shingle layers in place.
Working With a Roofer
If you’re thinking of adding another layer of shingles to your existing roof, contact a licensed and insured roofing company. They can come to look over your roof and let you know if this is a good idea or not. In most cases, roofers recommend against this approach, but there may be a few minor exceptions, such as sheds and outbuildings.
If you’re looking for a roofing company in the Greater Cincinnati area, contact Titan Siding and Roofing. Our knowledgeable roofers provide free inspections and can tell you whether roofing over your shingles is a wise choice.