One of the most common questions that roof services get from homeowners is whether it is essential to completely remove an old roof, or if new shingles can be installed over them. Faced with the expense of a new roof, many wonder if it is possible to save money by just adding new shingles over the bad ones. While it may be possible for a roofing company to do this, whether it should be done depends on many different things.

Roofing Over Old Shingles - What the Law Says

Every state has different laws about roofing, one of these laws specifically addresses the practice of adding new shingles over old. Since every layer of shingles adds more weight to the roof structure, roof services are required to abide by local building codes, which limits the number of layers a roof can have on it. Most states are limited to two or three layers depending on the roofing material used, and the pitch of the roof. However, even though multiple layers may be allowed by law, this does not mean it is a recommended practice.

Assumptions About Laying New Shingles Over Old

The biggest assumption about laying new shingles over old is that it will save the homeowner money, since they do not have to pay a roofing company to tear the whole old roof off. The second assumption is that with multiple roofing layers the roof is more protected, even if the underneath layer is old. While both of these ideas seem reasonable; unfortunately, they do not always work. In the end, many homeowners who attempt to save the work and money of completely tearing off the old roof end up with a greater expense when they begin to experience leaks, and then both layers must be removed.

Why Multiple Layers of Shingles Is Not Recommended

Laying more shingles on top of a bad roof is not going to fix the potential problems that could occur with that older layer. This is especially true if roofing services have already found that the roof is leaking, which frequently means the underlayment, and possibly even parts of the decking need replacing. Old shingles that are deteriorating will continue to do so, even if there is a newer layer on top of them.

Putting a new layer of shingles over an old layer also increases the chance that the top layer will not adhere well, or lay flat enough, both of which are necessary for the roof to be water resistant. Shingles that do not lie flat are also much more prone to being peeled off in high winds. An experienced roofing company will almost always recommend against the installation of new shingles over old ones for these and many other reasons.

Final Choices

The most important thing for homeowners to realize is that getting the best new shingle roof requires their roof services techs to fully remove the old one first. When multiple layers already exist, a roofing company should remove all layers before new shingles are installed. In circumstances where money prevents this, and the cost savings becomes a main factor, layering shingled roofs should be done with caution. Re-roofing should only be practiced over roofs that are not actively leaking, and have shingles that are still lying completely flat without buckling or curling. 

Homeowners must always keep in mind that a roof company is limited by law as to how many layers of shingles can be installed on a roof; and that regardless of financial circumstances, the old layers may have to come off anyway. A new roof laid directly over underlayment and decking also prevents the likelihood of premature shingle damage and leaking, which can end up creating an even bigger problem. Laying a new roof over the old one should only be done by roof services as a last resort!

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