The Correct Way to Replace a Residential Roof

Old Shingles

• You can add new shingles over the existing roof rather than tearing off the old shingles. The old shingles must be in relatively good condition for this method to work. You never add a third layer of shingles to a roof. Placing new shingles over old ones has certain disadvantages, however. You lose the chance to inspect the sheathing for any rot or decay, and a second layer of roofing material adds more weight that the roof framing must support. Also, some manufacturers will not guarantee their shingles unless you remove the old ones.

Fastening

• Shingles can be fastened by either nails or staples. However, nails have become the preferred method, and many building codes no longer allow staples. The shingle's connection to the decking is weakened when a roofer puts the nails in at a bad angle or places them too shallow or too deep. Since this can happen quite easily if the roofer uses a pneumatic nail gun, a reliable hammer remains the best way to fasten the nails.

Flashing

• The metal flashing, one of the critical roofing materials, covers weak points in the roof where water might enter. The roof valleys, where two sections of the roof meet, have a significant vulnerability to moisture and need strong flashing to avoid leaks. Chimneys also require the installation of metal flashing. Merely using a sealant around the chimney will not suffice, notes Tom Fieza, author of "How to Operate Your Home." He also advises building saddle flashing, metal flashing in a wedge shape, to divert water around a chimney more than 3 feet wide.

Tips

• Take advantage of having a roof replaced by installing new gutters if you need them. This can add a few days onto the time needed to finish the roof. All shingles have a certain weight; the heavier the weight, the longer the shingle lasts. If you live in cold regions, using a special type of bituminous material as flashing can help prevent ice dams, which allow water to build up behind them and leak into the home.