Installing a new roof is a sizable investment and most homeowners want to ensure that they’re being wise with their money. As a cost-saving measure, some may look to eliminate the cost of the tear-off of the old roof by simply roofing the new roof over the old one. It may seem like a good idea to put new shingles over the old ones, thinking that it may offer additional protection. We believe this mentality to be a penny-wise and dollar foolish for the following reasons:
Most homes in the Midwest are classified as “moderate hail zones”. When a home receives this classification, it is illegal to install a new asphalt roof over an existing one. Check your local ordinances to see whether this is even a possibility before moving forward with the project.
Asphalt shingles are heavy and adding a second layer of them to your roof may compromise your home’s walls and roof structure. Even if your area does permit shingles to be placed on your roof in multiple layers, eventually you will incur the cost of removing them because your roof can only support so much weight before its integrity is compromised.
Roofing manufacturers have warranties in place to protect consumers from the cost of replacing a roof should their product malfunction. Manufacturer warranties oftentimes will not cover new shingles being layered on top of old ones. The reasoning being that it is unlikely that the new shingles will be able to lay flat. If the shingles are not laid on a flat surface, they won’t conform to each other the way they are supposed to. Winds that the shingles should be able to stand up to may cause them to loosen. This leaves the homeowner with repair bills or the cost of replacing the roof sooner than they should have had to.
It’s improbable that your current shingles will line up with the existing ones. This will prevent the current shingles from sealing properly and as a result, they may come off during high winds easier than they normally would.
Roof Deck Inspection
A roof deck is the underlayment that shingles are laid on top of. By adding shingles on top of the old roof, there is no opportunity to inspect the roof deck to ensure that the current wood is not wearing out. Worn out portions of the roof deck can cause leaking. Stripping the roof down to the roof deck, also give the nails being used in the new roof a better chance to hold.