When cared for correctly, the average three-tab asphalt roof should be replaced at least every 18 to 20 years. If your home features architectural asphalt shingles, it will typically survive up to 30 years. However, there are factors that will shorten the lifespan of your asphalt roof, including weather damage and neglect.

Whether you have architectural or three-tab shingles, your asphalt roof will be covered with small granules. These granules serve several purposes, including protecting the asphalt underneath from the sun's rays and increasing the shingles’ fire resistance. As your roof ages, it's natural for the granules to fall off.

The first place you'll notice missing granules is inside the gutters. If there are a small number of granules missing and there are a handful of bare spots on the asphalt shingles, it is no cause for concern. However, if most of your shingles are missing granules and your roof is older, it's time to consider having the existing roof replaced.

Once again, the granules protect the asphalt shingle from ultraviolet damage. When the granules begin to fall off in large numbers, the asphalt beneath will weaken quickly, which can lead to further damage and leaks.

An obvious sign that your asphalt roof needs to be replaced is curling shingles. One major cause of asphalt shingle curling is the roof's age. Over the years, asphalt shingles will naturally dry out and shrink. Additionally, if your attic isn't properly ventilated, if the roof shingles weren't secured properly or if there are multiple layers of shingles, it can also lead to roof curling.

No matter the cause, if several of your asphalt shingles are curling, it is time to replace the roof. Eventually, the curling shingles will fall off altogether, leaving your home vulnerable to wind, snow and rain.

For many homeowners, mold and moss growth on their asphalt roof is unavoidable. However, if you keep this growth in check with regular maintenance, the presence of mold and moss is no cause for concern. It's when the mold and moss growth becomes extensive that homeowners have a problem.

In addition to causing damage to the shingles, the presence of mold and moss is often a sign of moisture problems. When moisture is trapped beneath the asphalt shingles, it can lead to decay. This decay provides the ideal environment for mold and moss to thrive.

If your asphalt roof is covered with moss or mold, contact a professional to not only have the roof replaced but also to pinpoint the cause of the infestation. This will help ensure your new roof doesn't need to be replaced prematurely because of mold and moss.