Can I add a second layer of shingles to my roof?

The short answer is yes, you can lay new roof shingles over the old ones. Let’s take a look at why some homeowners go this route and then we’ll consider a few reasons why we don’t recommend it. But before we get started, one thing must be clear: adding new roofing over old (sometimes called a “roof over or re-cover”) is possible only with asphalt shingles (also called “composition shingles”). You can’t do it with wood or metal, for example, and you should never mix materials, such as laying asphalt shingles over cedar shakes. Also, the old roofing has to be in pretty good shape.

Why do some homeowners choose to add additional layers?

Adding additional layers does not make a new roof any more waterproof, on the contrary, it often creates its own problems. The reason some homeowners choose to do it is to save time and money. By keeping the old shingles on, they skip the messy and labor-intensive tear-off step and they will save some money on the roof project. Even though you will save money in labor by not tearing off the old roof, you will need to do some special prep work (removing vents, ridge caps and warped shingles, among other things) and you still have to replace or add new flashing, which sometimes can be complicated over old roofing. Getting rid of the tear-off and disposal can easily save $1,000 to $2,000 depending on the size of your roof, but you’re really just delaying the cost: when it’s time to replace the roof again and you have no choice but to remove the existing shingles (two layers is the maximum allowed in most areas), you’ll have to pay extra for the two-layer tear-off and disposal.

Why adding additional layers is not recommended?

As we have seen so far, the potential cons of a roof over tend to outweigh the potential pros, but it all depends on your situation. The following list includes some reasons not to do a roof over as well as some things to check out if you’re seriously considering adding a second layer of shingles.

  • Shingles are designed for flat surfaces. Asphalt shingles are meant to be installed over a plywood deck. When adding a second layer of shingles, the bumps or imperfections from the old roof will transfer to the new layer. Your roof will not look as good as when you do a full tear-off.
  • Shingles add weight to your roof. Most likely, your roof structure was designed for a dead load of one layer of shingles, plus extra for snow and a safety margin. Installing new roof shingles over old doubles the weight of the roofing, so you must make sure your roof structure can handle the extra load. That’s also why building codes usually limit roof overs to no more than two layers. On some houses, the extra weight of multiple layer causes the roof decking to sag between the rafters or trusses.
  • No visual inspection of roof deck. In order to thoroughly inspect the roof decking and address any potential issues with it, you need to remove the existing shingles.
  • Unable to replace underlayment. The underlayment installed between the roof decking and the shingles is there to prevent water from coming in through the roof deck and into the attic. If the underlayment is old and damaged, it won’t protect your roof deck from the water that gets past the shingles.
  • Impact on warranty. Make sure you check with the shingle manufacturer regarding all warranty issues and installation requirements before adding a second layer.
  • Potential red flag for buyers. For many homeowners who are planning to sell their house in the near future, adding a second layer of shingles might sound like a good idea: why pay for a tear-off if you can just skip 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 having multiple layers of shingles. Because of this, home inspectors often warn the buyers of potential problems associated with roofs with multiple layers. As you can see, even if you’re selling your house, adding additional layers is not advantageous as it may discourage potential buyers.

In conclusion, Portland Quality Roofing Inc recommends removing all existing roofing material before installing your new roof. The temporary savings are just not enough considering the risks associated with re-covers.