Whenever you spot damage or signs of wear and tear on your roof, you'll wonder how costly it will be to repair. You'll also have to consider whether a fix will be enough to resolve the issue or if you're likely to experience more problems in the near future.

Deciding whether to repair or replace your roof depends on a number of factors, but you'll generally be required to assess the condition of your roofing materials. Jeanne Huber, writing for the National Association of Realtors' home improvement site HouseLogic, says you'll waste money if you replace a roof when the former one has plenty of years left in it. On the other hand, repairing the roof can also send your cash down the drain if a replacement is more fitting.

Perhaps the simplest way to decide what to do is to check out the whole area of your roof. At least once a year, inspect the shingles and other roofing materials to see if there are any problems. If you don't want to get up onto the roof for this process, you can use a pair of binoculars to inspect it from the ground.

There are several warning signs that your shingles need to be replaced. Owens Corning, a roofing and insulation company in Toledo, Ohio, says shingles should not be cracked or curling. They also should not be missing their granules, which help protect the roof against the sun's ultraviolet radiation. The shingles may look bald if these granules are eroding, or you may find the granules in the runoff of your downspout.

Black algae will leave dark stains on the roof, but only creates a cosmetic issue and can be removed with a bleach solution. Moss is a more serious problem, since it can retain moisture on the roof and damage the shingle granules. While moss can easily be scraped off, you'll need to take steps such as treating the roof with a cleaner and installing sheet metal coated with zinc or copper to prevent the problem from recurring.

Inspect around any openings in the roof as well. Huber says any flashing or caulk, such as that installed around a chimney, should be in good condition. You should also look for any wear around any vents, skylights, or pipes.

Most homeowners become aware of a roof problem when they discover a leak. Even if you don't hear dripping water in the attic, you may spot peeling paint near the roof overhangs or water stains on the ceiling, in the attic insulation, around the fireplace, or near pipes that vent through the roof. Shifflett Roofing & Construction, a company in New Orleans, says you may also notice wallpaper starting to peel.

Determine whether the leak is coming from the roof or some other source. Plumbing, radiators, or air conditioning systems can also cause leaks that affect the interior of your home. You can make an inspection during a rainstorm or when snow is melting off the roof, or you can try to pinpoint the leak by using a hose to gently spray water onto the top of your home.

Repairs are usually the best option for limited damage. For example, you may lose a few shingles during a particularly bad windstorm. Huber says repairs to unforeseen damage caused by a natural event can often be covered by your homeowners insurance.

When replacing shingles, it is best to find materials that match the existing shingles in color and style as closely as possible. In addition to creating a seamless look, it can also avoid disturbing potential buyers if you are planning to put the home on the market. Joe Provey, writing for the home improvement professional Bob Vila, says a large patch of mismatched roofing material can look especially suspicious.

Even if the damage is more significant, you may be able to address it with a repair rather than a complete replacement of the roof. Partial reroofing can be very expensive, but it will also be less expensive than replacement.

The age of your roof should play a part in your decision. John Rogers, writing for Angie's List, says most roofs will last 20 to 25 years. If your roof is nearing the end of its life expectancy, it may be more cost effective to replace it. Otherwise, your repair will only last for a few years, or until another problem arises and requires you to reroof the home.

One way to save money and get a new roof is to simply install new shingles over the old ones. However, Provey says this can only be done once; if the home has already been reroofed once in this way, you'll need to remove both layers and start over at the roof deck.

Reroofing over an existing layer of shingles carries other disadvantages as well. The shingles won't attach to the underlying shingles as well as they will to the roof deck, making them more vulnerable to wind damage. Huber says the roof will usually only be rated for 15 years and will have a more uneven appearance.

If you decide to replace the roof, take the opportunity to see if any other improvements are needed to this part of the home. You should inspect the roof deck for damage, and might consider installing a waterproof membrane to further protect your home.

You may also be able to get a discount on your homeowners insurance if you use roofing materials that are more resistant to fire or environmental damage. Once you've installed a new roof, you can also consider whether to put up a solar power system to reduce your energy bills.