There are a lot of perfectly legitimate reasons to consider laying a new roof on top of an older roof. Convenience and cost are the two biggest, and it makes sense. Without having to tear off your old roof, wouldn’t installing a new roof be a much easier, cheaper process?
That said, you’re right to be vary, vary wary if a local roofer suggests you simply install a new roof on top of your old one. In a vast majority of cases, the risks posed by “overlaying” a new roof far outweigh the potential cost and time savings.
Here’s what you need to know about installing a new roof over an old one.
Shingles Add Unnecessary Weight
Did you know that most areas’ building codes actually limit the layers of shingles at two? There’s a reason for that: Most roofs aren’t designed to hold the exponential weight of multiple layers of shingles. A single square foot of shingles can weigh upwards of 250 pounds! The structural integrity of your roof could be in jeopardy if you apply too many layers of shingles, so overlaying is a particularly risky option for older homes.
Your Old Roof Isn’t a Flat Surface
Shingles, particularly asphalt shingles like those most common here in metro Atlanta, are designed to be installed on a flat surface. They don’t do a great job sealing over bumps and humps, which your old shingles certainly create. Of course, an overlaid roof will be installed on top of a relatively flat underlayer, but if there are any cupped, curled, or misshapen shingles underneath, those defects will simply transfer onto the new layer.
Overlaying Doesn’t Reveal Anything
One of the best things about having a brand new roof installed (after your old roof has been removed) is that a professional roofer can take a good, hard look at what’s going on underneath. If decking, flashing, or any other components of your roofing system need to be shored up, they’re easily addressed once the shingles are off. If your old roof isn’t removed, roofers have to guess what’s going on underneath and there’s little that can be done to tackle slow-emerging leaks, cracks, or other foundational issues. Replacing the roof’s tar paper – the paper layer installed on bottom to keep your roof watertight – is one of the primary purposes of replacing your roof altogether.
Re-Roofing Can Void Warranties and Kill Home Sales
It’s entirely possible that the manufacturer’s warranty on your new shingles could be voided if you install the shingles on top of an old roof. If your roofer is encouraging you to install over your old roof, ask specifically to see a copy of the manufacturer’s product warranty. An overlaid roof can also serve as a “red flag” to homebuyers should you choose to put your home on the market. They might wonder – for good reason! – if you’re covering something up, or what’s going on underneath your old roof. Potential homebuyers will always find out if your roof has been re-roofed because any good inspector will note the condition on an inspection report.
If you’ve been advised to install a new roof, there are likely already significant issues present with your old one. It’s almost always best just to start fresh with a new foundation for your new roof rather than to re-roof. Why put a Band-Aid on the situation you’ll eventually need to address anyway?
