When it comes to any project, there’s usually a way to save a few bucks. Reroofing over your old shingles (shingles over shingles) is one of them. There are plenty of articles and how-to videos showing how to re-roof over existing shingles. Professionals also used to do it all the time. So then, based on this information, you should just layer shingles on. Right?
No.
Well, why not?
It comes down to some important factors. But having a reference point is also good, so take a look at the cost of a roof replacement in Calgary.
Does Installing Shingles Over Shingles Really Save Money?
If you’re considering reroofing over existing shingles, the main reason is usually to save money on the tear-off. So, you go ahead and get a new roof done on top of the existing shingles. Maybe you just want a different colour. But here’s the catch: even if the roof underneath is in good condition, you’ll still need to remove both layers when it comes time for the next replacement. If you’re curious, here’s what proper roof shingle removal involves. In reality, you’re not saving money, you’re just delaying the cost, and often worsening it down the road.
In a perfect world, all you’re doing is deferring payment. Unfortunately, more issues usually show up when you install shingles over shingles, especially if it’s done more than once.
The Problems With Installing New Shingles Over Old Ones
Why Layering Shingles Creates an Uneven Surface
A smooth, flat surface is key for a proper shingle installation. But when you install over existing shingles, the surface is already bumpy, and that creates a host of problems.
- Firstly, laying shingles on top introduces more stress because of the uneven surface, making them more prone to breaking and cracking before they reach the end of their lifespan.
- Secondly, fastening becomes more difficult. With extra thickness, nails may not be long enough to properly secure shingles to the roof deck. This problem gets worse with each additional layer.
Roof Weight Issues With Multiple Shingle Layers
Adding another layer of roofing materials adds significant weight, which strains your roofing system. In Alberta, heavy winter snow piles even more weight and really tests the structure. It’s one of the reasons why regular roof snow removal is so important. Smaller or older homes not designed for the added load are especially at risk.
How Shingles Over Shingles Affects Warranty, Insurance, and Codes
Most shingle manufacturers and insurance providers do not recommend more than one layer of shingles, and many don’t allow more than two under any circumstances. Even then, it’s not a best practice. According to the Alberta Performance Guide for Roofing, all shingles must be installed in line with the Alberta Building Code, which includes weight, ventilation, and structural requirements. Nothing in the code explicitly prohibits layering, but when you add weight and reduce ventilation, it’s much harder to meet those requirements properly.
Some roofers in Calgary will say it’s fine if the roof deck is solid and there’s only one layer underneath. We disagree. At Whalley’s Four Seasons Roofing, we’ve seen the long-term issues firsthand: extra weight, shortened shingle life, more leaks, and voided warranties. Our stance is simple, always tear off the old roof and install new shingles properly, so your home is protected the way it should be.
Why Leak Protection Is Harder With Layered Shingles
There are ways to seal over the top of an existing roof, but they’re rarely ideal. In Calgary’s climate, proper Underlayment and ice-and-water protection are essential. With a second layer of shingles, water can slip between layers more easily, leading to leaks and damage. If you’ve ever dealt with ice dams, you’ll know how important a good barrier system is.
Moreover, Calgary’s freeze–thaw cycles make things even worse. When water gets trapped between shingle layers, it can freeze and expand, creating cracks and hidden weak spots that aren’t obvious at first. Over time, this kind of damage spreads and makes repairs far more expensive than if the roof had been replaced properly from the start. What looks like a quick way to save money usually just covers up problems until they become much bigger.
Shingles Over Shingles and Home Resale Value
You might think adding shingles over shingles is smart when selling your, quick and cheap. But home inspectors and roofing inspectors report layered shingles to buyers right away. That often lowers the value of the home. It also raises red flags that other shortcuts might have been taken in maintenance. For peace of mind, it’s always smart to get a professional roof inspection before buying a home.
What to Do If Your Roof Already Has Multiple Shingle Layers
If your roof already has multiple layers, it’s worth scheduling an inspection. Best case, you just need to budget for a two-layer tear-off during your next replacement. Worst case, you could be facing foundation issues, ventilation problems, or wood rot from trapped moisture. Many of these problems show up in common Calgary roofing issues during winter. If you have more than two layers, get it checked right away. Waiting can lead to much more costly repairs.
Contact us for a roofing inspection to have that peace of mind for your home.
