Angieslist.com suggests that a typical asphalt shingle roof will last about 20 to 25 years, depending on variables such as the quality of the shingles, the professionalism of the installation, homeowner maintenance over the years, and, of course, the weather.

Your roof should have several lines of defense or redundancies. If one part fails, such as when a shingle blows off, there should be other protective layers such as an underlying membrane, flashing around chimneys and sealants that prevent the roof from leaking.

Because 70 percent of U.S. homes have asphalt or composition shingle roofs, replacement roofs tend to be similar. According to Roofingcalc.com, the average roof size in the U.S. is 1,700 square feet. Professional roofers calculate area by 100 square feet, so it would take 17 “squares” to reroof the average home. Materials and labor can run anywhere between $350 and $550 per square, or approximately $6000 to $9350.

Leaks through the ceiling, missing shingles, frayed or curling shingle edges, or erosion of the mineral granules are all signs that it’s time to repair or replace your roof.  Have your roof inspected by a reputable roofing contractor, who can tell you if the roof was properly installed and maintained.

Check with your homeowner’s insurance company about coverage. Insurance.com warns that many companies will amortize coverage according to the age of the roof and refuse coverage if the roof has two or more previous layers of roofs or if the roof is 20 years or older.