While you can install new shingles over old shingles, we highly recommend NOT choosing this method. It can save you a little money up front, but could lead to bigger problems and expensive repair costs in the future. Let’s talk about why you may or may not want to shingle over your existing roof during your reroofing project:
Why choose the shingle over method?
If you choose to cover your existing shingles with new ones, there are a couple reasons why this is a positive solution.
- Cost savings: How much you can save really depends on the pitch (slope) of your roof. On average, it’s about 15% of the total cost. To think about it in dollars, you’d save about $1/square foot of roof.
- Less hassle: Tearing off the existing shingles takes about up about 30% of the job site time, not including clean up. Skipping the tear off and disposal step allows the roofing crew to get started on installing your new shingles right away.
The main reasons homeowners choose to double roof their house is because it makes the roofing process less expensive and takes less time. You don’t have to pay for tear off and disposal, nor does the crew spend time initially taking off your current shingles. Additionally, between removing and installing new shingles, precipitation won’t undermine the project since there is a layer of shingles already there.
Why NOT to choose the shingle over method?
Most roofing companies are going to recommend tearing off your current shingles and starting fresh with a brand new layer of shingles (some companies won’t even consider placing shingles over shingles!). The sales representatives aren’t trying to just charge you more money because they have to hit a sales goal, but this is just best practice for the longevity of your roof and security of your home. Here’s why:
- Roof deck and underlayment go unchecked: When roofers don’t tear off your current shingles, they aren’t able to inspect the status of the roof deck and underlayment. These are two materials that exist under your layer of shingles that add extra protection for your home’s interior. If roofers can’t get underneath the shingles, they can’t identify any problem areas such as soft, spongy, or rotting spots in the roof decking (wood framing of the roof). The underlayment (a moisture barrier) could be deteriorated which limits the moisture protection from shingles to your roof deck then into your home. You would also not be able to add an ice and water shield if you’re in an area that experiences winter storms.
- Bacteria growth on the first layer: Any existing algae or moss on your roof are trapped and can tarnish your second shingle layer. This could cause the lifespan of your new shingles to shorten.
- Added weight: One square (100 square feet of roofing) weighs about 250-400 pounds. Double that weight and you have a great deal of added stress to your roof structure. This could cause any damaged sheathing to worsen and infiltrate your ventilation and insulation.
- Shingle installation is designed for flat surfaces: Shingles are designed to be nailed into the underlayment, which is a smooth flat surface. Roofers use nails to fasten the shingles down; nailing the new layer of shingles on top of the original shingles causes penetration to the bottom layer. This could lessen the hold the nail has, increasing the likelihood of shingles blowing off. Additionally, there are going to be inevitable bumps and spaces where the raised and lower parts of the first layer of shingles can’t match the flat bottom of the new shingles, compromising your level of protection from weather.
- Warranties are voided: With many shingle manufacturers, if you place a second layer of shingles on your roof, the warranty could become invalid.
- Tear off required next time: In most towns, building codes set the maximum to two roofing layers. Next time you have to replace your roof, you will be required to remove both layers and pay extra for the double layer tear off.
- Scares potential buyers: Home inspectors often report the double-layer roof to the potential homebuyers since this will be an added expense for them down the road. Two shingle layers could cause problems to arise if the reroofing job wasn’t completed correctly. This could be a big turn off, so if you’re thinking about selling your home, consider tearing off and only have one layer of shingles!
Are there other materials to put on top of asphalt shingles?
If you’re thinking about replacing your home’s roof with something other than asphalt shingles, you could potentially leave your existing roof alone, depending on your local building code. Metal roofing materials would go well over your shingled roof! While metal could be a slightly more expensive option, there are plenty of long term benefits to consider, especially not having to tear off your existing roof. This would only be recommended if your shingles are in good standing condition because your metal will last 50 years or so while your shingles could experience buckling before your metal’s life has been spent.
Talk to roofing experts before making a final decision. Allow them to conduct an inspection to determine the status of your current shingles and explore what financing options are available if cost is the main driving factor for shingle layering.
Ready to talk now? We are excited to discuss this topic with you! Contact us today.
Editor’s Note: This post was originally published in January 2019 and has been revamped and updated for accuracy and comprehensiveness in September 2020.