WHY ADD NEW ROOF SHINGLES OVER OLD ONES? (AND 9 REASONS NOT TO!)
When considering a roof replacement, simply adding new roof shingles over existing ones can be an option that homeowners consider. Our local roofing experts dive into the main reason why you might want to add new roof shingles over old ones, and 9 reasons why this isn’t a good idea. If you have any questions after reading this article, contact our team and one of our experts will get in touch with you shortly.
Initial Price. It seems simple; skip the first step of tearing off and save lots of money. While it’s true; it would save about $1,000 on the average size project, it really hurts in the end which is why we don’t do it as a company. The savings is made up of the labor to tear off the old shingles, as well as the costs to take them to the recycler.
However, this savings benefit has its caveats. It's clearly easier to leave the old shingles in place, but there's some special prep work involved with a re-roof (removing vents, ridge caps and misshapen shingles, among other things) and you still have to replace or add new flashing, which sometimes can be tricky over old roofing. All of that fumbling around can add up quickly with additional labor and materials, and you're really just delaying the cost: when it's time to replace the roof again and you have no choice but to start new again since two layers is the maximum allowed in California.
Why Not Add New Roof Shingles Over Old?
As suggested above, the potential cons of re-roofing tend to outweigh the potential pros, but it all depends on your situation. The following list includes some universal reasons not to reroof as well as some considerations or things to check out if you're seriously considering adding new roof shingles over old ones.
1. Bad look. Shingles are made to be laid flat; they don't do a good job of bridging gaps, dips or humps, including the stepped texture of overlapping shingles. Re-roofers have tricks to lay new roof shingles over old so that the same step-ups between courses are maintained, but if any old shingles are cupped, curled or missing, those defects will show through to the new roofing layer. Many roofers recommend using laminated, or dimensional, shingles for re-roofs because they're thicker than standard shingles and often have a staggered edge profile (for looks) that helps hide any dips or high spots in the old roofing.
2. Shingles add weight. Typical shingles weigh around 4 pounds per square foot, and chances are your roof structure was designed for a dead load of only one layer of shingles, plus extra for a safety margin. Installing new roof shingles over the old effectively doubles the dead weight of the roofing, so you have to make sure your roof structure can handle the extra load (which most roofers who are willing to install over the old will not do). That's also why building codes commonly limit re-roofing to no more than two layers. On some houses, the extra weight of multiple layers causes the roof sheathing to sag between the rafters or trusses.
3. No inspection of roof sheathing. This is our biggest reason that we, as a company, do not install roofing over old roofing. Without a clean tear off, our roofers can't see what the base wood looks like. A good roofer will perform a careful "walking" inspection for spongy areas and other problems, and they can make localized repairs before re-roofing. A not-so-good roofer might be less conscientious.
4. Can't replace underlayment. The underlayment that is laid between the roof sheathing and the shingles is there for a very good reason; water has a way of getting under shingles, no matter how many layers of roofing you have. If the underlayment is old and deteriorated, it won't protect your roof deck from water that gets past the shingles. We also use a self adhering membrane in the valleys for additional water proofing, and adding this membrane is not an option with a lay-over roof.
5. Lay-over roofing is rarely warrantied. This one is pretty self-explanatory. Be sure to check with the shingle manufacturer regarding all warranty issues and installation requirements before any roof project.
6. Local codes might not allow it. Two layers is the maximum in most areas, and some building codes allow only for one. This can be caught by an inspector or code enforcement officer at any time in the future, leading to a costly fix.
7. Shorter life span of the roof. Two layers of shingles are going to attract and retain a lot more heat than just a single layer, which can lead to the shingles prematurely deteriorating. Also, what about all that dark algae growth and bacteria on the original layer of shingles? Now all of that is trapped under a 2nd layer of shingles, again having the potential to shorten the lifespan of the top layer of shingles.
8. Flashing. A roofer who is willing to install new roofing over the old roofing without considering all of these points spelled out here, is probably not going to replace any of the flashing which keeps the water out of your home. Typically, we see evidence of adding some caulking around the old flashing, which may last a year or two, but not much more. If they are replacing the flashing, the additional labor that is required to work around the old shingles adds to the costs, chipping away at any potential savings.
9. Lay-over roofing does not look good on an inspection report. Adding new roof shingles over old ones is tempting to a lot of people planning to sell their house in the near future: why pay for a tear off if you can get away without it? Of course, it'll be the new owners who are stuck with the extra expense of a two-layer tear off down the road, along with any problems arising from an improper roof job. Because of this, home inspectors often report double-layer roofs when they find them, and they may warn the buyers of potential problems associated with lay-over roofs.
10. Long term price. Well, that’s odd; that reason is similar to the first and only reason to install new roofing over the old shingles! Well, the big difference it the ‘Long term’ Price. What we mean is, sure, you can save some money now, but long term, with the additional tear off and disposal of two layers later, and the potential for a lot of missed wood damage which can cost even more to do when it’s in worse shape than it is now, the additional costs and far exceed the little that was saved now.