When patching stops being worth it

Daylight or damp in the attic

Go up on a bright day with the lights off. Pinpoints of daylight through the deck, dark staining on the sheathing, damp insulation or rust running down a nail shank all say water is getting in and has been for a while.

Repeated repairs in different places

One leak is an event. Three leaks in three different areas inside two years is a pattern, and the pattern means the covering has reached the end of its service life rather than suffered a specific failure.

The age on the paperwork

Age alone is not a reason to replace. Age plus any one of the symptoms above usually is.

Granules in the gutter

The granules are the sunscreen. Losing them in volume means the asphalt beneath is being cooked directly, and from that point the roof ages in years rather than decades.

Sagging along a line

A ridge or a plane that dips is a structural signal rather than a covering one. It usually means decking that has been wet long enough to lose strength, and occasionally framing. This is the one symptom that should not wait.

Shingles that curl, cup or go brittle

A roof near the end goes hard. Shingles that were pliable enough to seal down in the sun no longer bond, and the first serious wind takes them.

In short

If two or more of these apply, get somebody to look at it and give you a remaining-life number in years. That single number turns the decision from a worry into arithmetic.