It may be surprising to learn that most building codes do not allow roofers to repair an existing double-layer roof. Insurance companies see the value of replacing old double-layer shingles with a new single-layer one. There are some situations in which it is necessary to tear off the roof completely. As mentioned earlier, homeowners are legally limited to two layers of roof tiles.
So, if you already have two layers, you'll need to remove them completely. In addition, if the roof is heavily damaged, it is likely that it cannot withstand the weight of a new roof and will need to be torn off. Ultimately, it's best to work with a roofing professional to determine if your roof is eligible for re-roofing. If so, you're likely to save quite a bit of money if you leave your existing roofing system in place under a new layer of shingles.
The opportunity to assess the condition of your roof covering is valuable, insofar as you can check if the wood is rotten and the presence of inadequate fastening elements. Once you've decided to re-roof, you'll need to decide whether to install your new roof over the existing one or if you're going to tear off the old one. Both of these costs may increase if several types of roofing material are involved for disposal. ExperTroofer is right, but you can add it to what you have by gradually accumulating tiles so that everything sticks together, you want the water to drain and not accumulate anywhere.
Even if only part of the roof shows signs of wear and tear, it's wise to consider doing all the work while the crew is on site with their scaffolding, ladders and equipment. By making the necessary repairs and adding fasteners to the coating (especially nails or ring screws), you will avoid drastic losses that occur when the coating comes off the roof, allowing rain to cause major damage to the interior. Contrary to intuition, partial roof renovation work is more expensive in terms of cost per square (an area of 10 feet x 10 feet). If you choose the latter option, you'll also need to decide if you're going to cover your existing roof or if you're going to remove it.
Repairing a section of the roof will also make it easier to mix the new with the old, since slight differences in color will be less noticeable. Therefore, in addition to increased labor and disposal costs, there may be an uneven effect on the ridges, as the old roof will end up a couple of inches taller than the new one. Starting the roofing work with a clean cover (removing old tiles and felt from the roof) also means that you have the option of adding a membrane that protects ice and water along the eaves. While this may seem like a way to save a few dollars, untrained homeowners can cause serious damage to their roof (or to themselves) if they use incorrect or irresponsible roofing techniques.
If the damage is more significant but is limited to one side of the roof, partial roofing is an option that will cost thousands of dollars less than repairing the entire roof.
