Re-roofing is a method of installing new shingles over the old ones so that the old shingles effectively become the underlayment for the new roof. This method of roof installation is typically chosen either to save money or to install new roofing when the old roof is relatively functional and undamaged.
1. Roof Inspection
Re-roofing can only be completed if the basic structure of your old roof is sound, and if the shingles aren't beginning to decompose. Your roofer will inspect both the exterior of the roof and the underside of the decking, via your attic, to determine if your home is a candidate for re-roofing. The roofing contractor will be looking for problems, like sagging sections of the roof or water damage on the interior of the roof. If these are found, re-roofing may not be an option.
2. Load Verification
Every roof is built to hold a certain amount of weight. This load limit is usually codified, and most homes are built to code. Your roofer will verify the load limit for your roof, then they will do a quick calculation to ensure that re-roofing won't put you over that limit. They must figure in the weight of the old shingles and new shingles, plus any additional weight, such as from snow, that could be placed on your roof. If the load comes up to less than the limit, your home can be re-roofed.
3. Level the Roof
Although the old roof can't have any major issues, small issues like loose decking nails or a few damaged shingles aren't a big deal. Your roofing crew will need to prep the roof before laying new shingles to ensure there is a flat, level surface. They may fasten down loose decking and nail down shingles that have become loose or are beginning to curl.
Now that the prep work is done, the new shingles will be installed directly over the old ones. Since there is no teardown or laying down of roofing tar paper, this process should go relatively quickly. The roofers may remove shingles along the eaves of your roof and replace them with a drip edge, but generally, there will be no shingle tear-off beyond this.
5. Trim Repairs
The final step is the same for both traditional roofing and re-roofing. Your roofing crew will replace any damaged or worn-out trim and make repairs to the eaves as necessary. Vents and other rooftop penetrations will be flashed and sealed to the new shingles so there will be no leaks.
Contact a re-roofing service to learn more about your new roof options.