In some situations, it is technically possible to install new asphalt shingles directly over an existing layer in Quebec. However, most certified roofers in Gatineau and Ottawa recommend against it. While roofing over old shingles can reduce the upfront cost of a project, it introduces a range of technical and warranty complications that often result in higher costs over the long run.
When Is It Technically Permissible to Roof Over Old Shingles?
Under the National Building Code of Canada as adopted in Quebec, a second layer of asphalt shingles can generally be installed over one existing layer, provided the existing roof deck is structurally sound, existing shingles are flat and not heavily buckled, attic ventilation meets current code requirements, and the additional weight does not exceed the structural design load. The Regie du batiment du Quebec governs these standards for residential construction — your contractor’s RBQ licence number confirms they are qualified to assess and certify compliance.
Why Most Certified Roofers in Quebec Recommend a Full Tear-Off
A full tear-off allows the roofer to inspect and repair the roof deck before installing new materials. It removes trapped moisture that would otherwise continue to deteriorate the wood underneath. New ice-and-water shield and underlayment can be properly installed across the entire surface. And it avoids the additional weight of a double shingle layer, a concern in a snow-heavy region like Gatineau. Our shingle roofing service at Cossette almost always includes a full tear-off as the default approach, ensuring a complete, warranted installation that performs as expected through Quebec winters.
What Roofing Warranties Say About Installing Over Old Shingles
Most major shingle manufacturers allow their materials to be installed over one existing layer, but only under specific conditions. Warranty coverage is often reduced in overlay scenarios, and the full workmanship warranty may not be available unless deck and underlayment conditions are verified and documented. Always ask your roofer for specific warranty terms before making a decision.
What Cossette Roofing Recommends
Cossette Roofing evaluates each roof individually during a free inspection. In most cases, we recommend a full tear-off to protect your investment and ensure a complete, fully warranted installation. We will advise on overlay only when the conditions genuinely support it and the homeowner has made an informed choice. Request a free quote and we will provide a side-by-side comparison of both options for your specific roof.
Frequently Asked Questions
Is it allowed to install new shingles over old ones in Quebec?
Under the National Building Code of Canada as adopted in Quebec, a second layer of asphalt shingles can generally be installed over one existing layer, provided the existing roof deck is structurally sound, existing shingles are flat, attic ventilation meets current code, and the additional weight does not exceed the structural design load.
Why do most certified roofers in Quebec recommend a full tear-off?
A full tear-off allows the roofer to inspect and repair the roof deck, remove trapped moisture, properly install new ice-and-water shield across the entire surface, and avoid the added weight of a double shingle layer. In a snow-heavy region like Gatineau, this added weight is a real structural concern.
Does installing new shingles over old ones affect my roofing warranty?
Yes. Most manufacturers allow overlay installations under specific conditions, but warranty coverage is often reduced. The full workmanship warranty may not be available unless deck and underlayment conditions are verified and documented. Always ask your roofer for specific warranty terms before choosing an overlay installation.
Does roofing over old shingles save money in the long run?
Not typically. While overlay reduces upfront labour costs by eliminating tear-off, it may lead to higher long-term costs. Trapped moisture can accelerate deck deterioration, hidden damage goes undetected, and warranty coverage may be limited. Over time, these factors often result in earlier-than-expected replacement needs.
What does Cossette Roofing recommend — overlay or full tear-off?
Cossette Roofing evaluates each roof individually during a free inspection. In most cases, they recommend a full tear-off to protect your investment and ensure a complete, fully warranted installation. They advise overlay only when conditions genuinely support it and the homeowner has made an informed choice.