When it’s time to replace a roof, many Canadians wonder: Can I install new shingles right over the old ones? It’s a tempting idea – saving time, labor, and money. But is this shortcut really a smart choice for the Canadian climate?
In this article, we’ll break down the key considerations: when it’s okay to shingle over existing layers, when it’s a bad idea, the pros and cons, and what Canadian building codes have to say.
What Does “Overlay” Mean?
Overlaying means installing new asphalt shingles – the most common roofing material in Canada—right on top of the existing layer without tearing off the old one. This creates a two-layer system.
Benefits of Shingling Over Existing Roofs
- 💰 Cost Savings
One of the biggest advantages is cutting costs. Removing the old shingles and disposing of the debris can run anywhere from $1,000 to $2,500 depending on roof size and location. Overlaying skips this expense. - ⏱ Faster Installation
The job goes quicker since there’s no need to tear off the old roof. This can be a big advantage if bad weather is approaching – especially before winter sets in. - ♻️ Less Construction Waste
This method is more environmentally friendly, sending less waste to landfills.
What’s the Catch? Risks and Downsides
Despite the perks, there are several reasons why laying new shingles over old ones might not be a great idea.
- ⚠️ Not Always Permitted
Most Canadian municipalities allow only two layers of asphalt shingles. If your roof already has two, a full tear-off is mandatory. Some cities may require removal even if there’s just one layer. Always check your local building codes before starting the job. - 🏚 You Can’t Inspect the Decking
Skipping the tear-off means you can’t check for water damage, mold, or rot beneath the old shingles. That hidden damage can lead to early failure of your new roof, no matter how good it looks from the outside. - 🌡 Extra Weight on the Structure
Shingles are heavy – around 100–150 kg per 10 m². Adding a second layer nearly doubles the load on your roof structure. That can be dangerous for older homes or roofs not built to handle the added weight. - 🌬 Higher Wind Damage Risk
In windy parts of Canada – like Alberta or the Atlantic provinces – adding new shingles over old ones can reduce wind resistance. The layers may lift or peel, especially if the original shingles are already worn or damaged.
When Is It Okay to Shingle Over?
Overlaying may be a viable option if all of the following are true:
✅ You have only one layer of existing shingles
✅ The old shingles are flat – no curling, blistering, or cracking
✅ There are no signs of water damage or rot
✅ The roof structure is in good condition
✅ Your local building code allows it
In this case, overlaying can be a reasonable short-term solution. If you’re considering this route, it’s wise to get in touch with professionals offering roofing services in Calgary to ensure your structure meets all the requirements.
Pro Tip: Use an Underlayment
Even if you’re overlaying, it’s strongly recommended to install an underlayment – a waterproof membrane between the old and new layers. Especially in colder climates, this extra layer adds moisture protection and extends the life of your roof.
When Should You Avoid It?
Shingling over old material is not advised in the following situations:
❌ There are already two layers of shingles
❌ You see signs of moisture, mold, or structural sagging
❌ The roof is over 20 years old and hasn’t had major repairs
❌ You need to upgrade ventilation, insulation, or other components
❌ You’re planning to install a metal or alternative roofing system
In these cases, a full tear-off is the right move.
Bottom Line: Overlay or Tear Off?
Installing new shingles over old ones can be an acceptable solution – but only under the right conditions. In dry areas with mild winters, like parts of southern Alberta, it might work. However, in most cases, a full replacement is the safer, longer-lasting choice.
To make the right call:
- ✅ Get a quote from a licensed roofer
- ✅ Check your local building codes
- ✅ Inspect the current roof’s condition thoroughly
If you’re local, consider getting a roofing estimate in Calgary to compare the costs and weigh your options properly.
Tip: If you’re planning to sell your home, a full roof replacement is the better investment. Buyers prefer the peace of mind that comes with a brand-new, single-layer roof – not a patchwork job.
