Do you need a new roof?? Let's look at a few things.

Making sure your roof is solid and doing its job is very important. Look at these key areas to see if yours is in need of replacing.

25 years is about the max a roof can last.

Typically an asphalt shingle roof should last between 20 and 30 years according to The National Association of Home Inspectors.

If you have reached 25 years with your roof you probably have about 5 to 10 years, depending on your roof's condition. Also consider that all of your neighbors are starting to replace their roofing, it could be a sign that you should do the same.

If you see that the shingles are curling, it is time.

According to the National Roofing Contractors Association, shingles can curl in two ways: there's cupping, which happens when the edges of the shingles turn upward; and there's clawing, which is when the edges stay flat and the middle starts to come up. Both are signs that your roof is either already leaking or will soon have issues.

When entire shingles are missing, you may have a little time, but it might not be pretty.

If you look at it from a functional standpoint, there should be no problem with just replacing a few shingles here and there. The thing to know is this, if you are wanting a uniform look, you are probably out of luck. Shingle color availability changes, they discontinue some year by year, the weather fades the shingles that are in place and so you may end up having a patchwork quilt looking roof.

You usually can keep patching until a bigger issue appears.

If you have shingles that are cracked, it depends on where and how many.

Cracked shingles are typically a result of wind damage. If just a few shingles are cracked, you can certainly replace them. But keep in mind that if the cracking isn't isolated to one particular area and it's random throughout the roof, it is time to look at a new roof.

Usually once the cracking is visible, you will most likely have to replace the whole thing within three to five years.

If you are finding granules in the gutter, keep this in mind.

If you have a new asphalt roof and find granules in the gutters or scattered around, don’t worry those are just "extras." BUT if your roof is 10 to 15 years old then it is a sign of a bigger problem. Why? Granules help keep the sun off the asphalt and once the granules fall off and the shingles start to bake, your roof will deteriorate in a hurry.

No need to panic when the shingles are covered with moss or algae.

This is just a cosmetic issue and some people may choose to replace the roof just because they don't like the look of it. If you choose to replace your roof because of this, it is good to know that a lot of new shingles are algae-resistant.

Whatever you do don't take matters into your own hands by power washing or scraping at the algae and moss. You will inevitably chip off all the granules, which essentially renders your shingles useless.

You can use a wash that is one part bleach and one part water to remove algae or moss. Or, according to Good Housekeeping magazine, look into zinc strips that can be installed at roof peaks and will eventually eliminate the problem.​​

Seeing sunlight from your attic is not a good thing.

Look at it like this, if light can get in, so can rain, air and snow. Small leaks can be patched, but larger ones, structural damage, and the age factor might point you in the direction of a replacement.

It is time to worry with your entire roof is sagging.

A sagging roof is typically an indication of a structural issue, usually stemming from the decking in the attic or, worse, with the supports in the foundation.

Bottom line is, if you see a depression or a droop, call in an expert as soon as you can.

Source: http://www.goodhousekeeping.com/home/renovation/a34020/when-to-replace-your-roof/