There are several signs that a roof may need to be replaced, including:

1. Age: Most roofs have a lifespan of 20 to 25 years, after which they start to deteriorate.

2. Visible Damage: Signs of visible damage such as cracked, missing or curled shingles, rusted or missing flashing, or damaged roofing tiles, etc. may indicate that your roof is vulnerable to damage.

3. Leaks: Any signs of water damage on your ceiling or walls could be due to leakages from your roof.

4. Granule Loss: If you notice that granules from the shingles are clogging the gutters, this could be an indication that the roof has reached the end of its lifespan.

5. Sagging: Sagging or drooping rooflines could be an indication that the underlying structure has weakened over time, causing the roof to droop or sag.

6. Energy Bills: If you notice your energy bills are increasing and the insulation and ventilation of your roof are already in their top shape, it could be that your roof is not performing correctly.

7. Moss or Algae Growth: If moss or algae is growing on your roof, this may indicate that there is trapped moisture on your roof or the roof is deteriorating.

If you notice any of these signs, it may be time to contact a professional roofing contractor to evaluate the condition of your roof and recommend any necessary repairs or replacement.