You have several missing or loose shingles.
This could be due to storm damage, or it may be because your roof is past its prime. When shingles become loose or fall off, your roof, as a whole, isn’t going to be very useful in protecting your home.
Your shingles are curling, cracking, dry, or blistering.
If your shingles begin to show any of these signs, it usually means they have reached the end of their life, and you probably need to have a new roof installed. Blistering could also be due to high humidity levels (contact with too much moisture), which is usually the result of a poor roof ventilation system.
The roof is sagging.
A sagging roof could mean several things: your roof could be weak and deteriorating; it could have been installed improperly; or it might be supporting too much weight (snow, ice, etc.). Whatever the case, roof sagging is a clear sign that your roof needs to be replaced. If you don’t act soon, it could collapse.
There are dark/dirty areas on your roof.
Darker areas usually appear when granules begin to fall off shingles. This means your shingles have aged and should soon be replaced. Dark patches could also signal algae or moss growth on your roof, which should be removed as soon as possible.
You have granules in your gutters.
When shingles begin to lose granules, it means they have reached an age where they aren’t as effective as they should be and must be replaced. Shingles lose more and more granules as they get older.
You notice several exposed or loose nail heads.
If nails begin popping out of place, the holes and spaces around the nails that remain are susceptible to water penetration and can lead to leaks in the roof. The damage this moisture causes might force you to replace your roof sooner than expected.
You have water damage inside your home or attic.
If you have water leaking into any parts of your home or attic, there’s a good chance that your shingle underlayment is inadequate or flashing on your roof has deteriorated. Mold and mildew can result from inadequate roof ventilation.
There are areas where flashing is missing or damaged.
Flashing is placed around projections that intersect with your roof, such as your chimney. If the sealing around these structures is broken or damaged, water can easily leak into your home.
Your roof is over 20 years of age.
If you have an asphalt shingle roof, it will typically last 20-25 years before it needs to be replaced. If your roof was installed over the top of the previous roof (shingles on top of shingles), then you may need to replace your roof sooner.
Your heating and cooling bills have gotten noticeably higher.
This could be a result of insufficient attic ventilation or a damaged/leaky roof that lets bad air in and good air out.