How do I know if a roof needs replacing or just repairing?

Age and the pattern of the damage decide it. An asphalt shingle roof in this climate lasts roughly twenty to twenty five years. Damage confined to one slope or one area after a storm is a repair. Granules collecting in the gutters, shingles curling at the edges across the whole roof, or a second layer already installed over the first all point to replacement. Repairing a roof in its final years costs money twice, because the next leak arrives before the repair has paid for itself.