Yes, you can put shingles over shingles, but you shouldn’t. Other factors to consider include weight increase, surface defects, and the prevention of full inspections.
Why You Should Not Add New Roofing Shingles Over Old Ones
There are a few universal reasons not to reroof with new shingles. Here are things to check out if you are seriously considering adding your new roofing shingles over top of the old ones.
Shingles Add Weight
Your roof is likely graded for a very specific amount of weight. This is factoring in the shingles and potential snow that could also accumulate. When you add extra materials over the top, you only add weight to the existing structure.
This creates an issue regarding how much your current roofing structure can handle. If you overload the roof, there is a chance that it may not be able to hold up. When this becomes a possibility, there is a chance that your home’s structure is unsafe with the chance of a potential collapse.
Shingles are Designed for Flat Surfaces
Shingles are not meant to bridge over gaps, humps, or dips. This includes the stepped texture that is created by overlapping shingles. While some experienced roofers have tricks for laying new roofing shingles over the old, there is still a chance that they are curled, cupped, or misshapen.
These defects will then telegraph throughout the new layer. If you decide that you absolutely have to re-layer your roof, use laminated or dimensional shingles since they are thicker and offer staggered edge profiles that help to hide any high spots or dips that might be in the old roofing.
No Visual Inspection
Without that tear-off process, roofers cannot see what the decking underneath looks like. A roofer worth their salt will perform a careful inspection, known as a “walking” inspection, to look for spongy and problem areas. This allows them to make localized repairs before the re-roofing process.
When you hire a less-than-reputable roofer to do the job, they might not bother with this portion of the process. This leaves your roof susceptible to any damaged areas, which could permeate through the new layer of roofing shingles.
There is a litany of reasons why it is not a great idea to shingle over top of an existing layer of shingling simply. Understandably, some don’t want to fork out the upfront costs of new roofing installations, but it is beneficial to not roof over the older roof layer in the long run.
The reasons above should be enough to deter you from simply laying the new roofing shingles over top of the old ones but just know that there are even more reasons why it is not a good reason to do so. You might save in the short term, but it will definitely cost you in the long run.
Take the necessary precautions when laying down your new roofing shingles and, if at all possible, remove the previous layer before doing so. It will save you a lot of trouble in the end.
Is It Possible to Put Shingles Over Shingles?
Placing old shingles over new ones is only possible with asphalt shingles, also known as composition shingles. You cannot place a new layer over top of slate or wood, and you should definitely never mix materials like laying asphalt shingles over cedar shakes.
And perhaps the most important rule for laying new shingles over top of old ones is that the old roofing has to be in pretty good condition. If you are laying new roofing shingles over an existing roofing system with a ton of leaks or damage, you aren’t doing yourself any good.
There may come a time when your existing roof just isn’t doing what it should. Leaks, broken shingles, and a litany of other problems can creep up, bringing you to the conclusion that you need to make a change to your current system.
Why People Add New Roof Shingles Over Top of Old Ones
The biggest reasons people lay down new shingles over existing ones are convenience and cost. Keeping the old shingles allows you to skip the messy labor and disposal costs of a tear-off. Also, having multiple roofing layers can create problems all its own.
It is important to note that both of these have caveats. It isn’t as simple as putting the new roof over the top of the old; special prep work needs to be done to complete the new installation. Things like removing ridge caps, vents, and misshapen angles are just the tip of the iceberg.
In addition, you might still have to replace or add new flashing. This can sometimes be tricky to do over old roofing. And the fact is that while you might be saving tear-off costs, you really are just delaying the cost. When you have to start over with a new roof, you’ll just have to tear it off and start over.
Putting new roofing over the existing structure is a “pay me now or pay me later” scenario. You will save on costs in the short term, but you will eventually need to pay for the full cost of a new roof at some point.
Final Verdict
It might seem like an obvious benefit to having multiple layers of protection on your roof, but that is not automatically true. As a matter of fact, having multiple layers of shingles does not mean that your roof is any more waterproof than it may have been before.
As a result, putting new shingles on top of old ones is a bad idea and a bad roofing practice. Furthermore, it is unlikely to save you as much money as you project because of long-term complications and other mitigating factors.