You can only install a new roof over an old one if the old roof is completely flat and level. Several factors can cause the existence of curly shingles; therefore, it is advisable to involve a professional roofer to determine the cause and replace the shingle before proceeding to a new roof. One of the main and simplest reasons why an overlap is not possible is when you don't have asphalt shingles. Installing a new roof over an existing one can only be done if you have shingles because you can only lay shingles over shingles.
It is not possible to mix materials or install a new layer on slate or wood tiles. Except asphalt shingles, no other roof covering for pitched roofs allows you the recovery process, directly over the existing roof covering. Roofing is not the same as roof replacement and there are certain conditions that your roof must meet to be a viable candidate for reroofing. This, together with the subfloor, roof covering and the original layer of shingles, will work as a combined protection against damage and prevent any leaks from entering your home.
When your roof starts to fail, but is generally in good condition, a new roof might be the best option for you. Some roofers install a waterproof shingle base layer (WSU) over existing shingles at the end of the eaves, as would be done with a roof placed over a bare siding. If you know it's time to install a new tile roof or even a shingle roof in your home, you may have heard that you can lay a new layer of shingle over your existing one. In some houses, the additional weight of the multiple layers causes the roof lining (roof) to sag between the rafters or trusses.
Even with all the benefits of installing new shingles instead of old ones, there are times when it is better (or even necessary) to tear off the old roof and start over. Installing new shingles over old ones effectively doubles the dead weight of the roof, so you need to make sure that your roof structure can withstand the additional load (which most roofers who are willing to install over the old one will not do). If you are still struggling between re-roofing and replacing the roof, you should contact a professional roofing contractor to find out which path is most beneficial to your home. Saving a thousand dollars with a simple roofing change may seem attractive now, but the associated costs of a later replacement due to poor foundation certainly won't.
If you plan to move in the near future, re-roofing could lower the value of your home and make it more difficult to sell. You'll save on short-term costs, but eventually you'll have to pay the full cost of a new roof at some point. Because of this, home inspectors often report double-layer roofs when they find them, and can warn buyers of possible problems associated with overlapping roofs.