It is possible to lay new roofing shingles over old ones. However, some limiting factors may come into play when considering this option. But before looking into this, it is prudent to understand some of the reason for wanting to lay new shingles over old ones.
Essentially, this is something called re-roofing, and it only is possible when dealing with asphalt shingled roofs. It does not work with the slate and wood shingles. Moreover, you cannot mix the materials when doing a roofing overlay. That means you cannot use asphalt shingles to lay them over cedar shakes.
Why Place New Roof Shingles Over The Existing Ones?
You can be forgiven for thinking that having several layers of shingles will enhance the waterproofing of your roof, but that is a misconception. Instead, what it can do is create unique problems. But if that is the case, then why would you consider laying new shingles over old ones? The issues of convenience and cost spring up because you will not have to worry out the time and cost of labor needed to rip out the old shingles. As such, you will be able to save some money on the reroofing project.
But even then, these benefits have caveats. For instance, you will have to do some special prep work on the old shingles, such as removing the worn-out shingles, vents, and ridge caps before reroofing. You also will have to add or replace the flashing, which may be a bit tricky to do over old asphalt shingles. Overall, you may be saving money when by avoiding the need to tear off the old shingles. But you also are only delaying the inevitable costs that will come up when you eventually need to replace the entire roofing system. That means you will have two layers of shingles to tear off, and this will require you to pay extra.
Or call: (612) 712-2877
Why Adding New Roof Shingles Over The Old Ones May Not Be Advisable
1. Ideally, the shingles are meant for flat surfaces. They are not the best choice when you want something that will bridge over gaps, humps, and dips. And the stepped textures the overlapped shingles create is also another concern.
2. Every shingle has a certain weight, and many of them on a roofing system will make it bulky. The quality asphalt shingles weight around 350 – 450 pounds per square feet of roofing when installed. With the standard roof structure designed to support the load of one layer of the asphalt shingles while also accounting for things such as snow, things go off when another layer of shingles is installed. Therefore, reroofing doubles the weight of your roofing.
3. Because there is no tear-off being done, there is no visual inspection of the roof’s sheathing. As such, roofers do not know the state of the underlying decking. And if you are working with a less conscientious roofer, then they may not take the time to carefully walk on the roof to check for spongy areas and other underlying problems that need fixing before reroofing.
4. Since no tear-off is done, then replacing the underlayment also cannot be done. The underlayment, which is tarpaper designed to make the roofing system watertight, may be worn out by the water. And if the tarpaper is old and deteriorated, it will be weak and not able to protect the roofing deck from water that gets past the layers of asphalt shingles.
5. By opting to reroof your home, you may affect the warranty of the new asphalt shingles. Therefore, it is wise to check the manufacturer’s warranty and installation requirements before placing the new shingles.
6. Some local building and construction regulations might not allow overlaying of shingles if there was another prior reroofing. The standard limit is two layers, and some states only allow one layer. For instances, towns in regions that experience heavy storms or roofing ice dam problems do not allow layering of shingles.
7. The asphalt shingle reroofing may not have a positive impact on an inspection report. Many people that are planning to sell their houses will consider reroofing. But it is wise to review all the effects of such a decision before its implementation.