Water entering a roof does not immediately appear on a ceiling. It soaks into decking, runs along framing, and gets absorbed by insulation. By the time it stains a ceiling, it has usually been getting in for some time.
Look in the attic
The most useful roof inspection available and the one almost nobody does. You are looking at the underside of the roof from inside, which shows things invisible from outside.
Daylight. Visible light where there should not be any means a hole. Where there is a hole there is water.
Staining on the decking. Dark patches indicate water has been reaching that spot. Note the location — it tells a roofer where to look.
Damp or compressed insulation. Insulation that has been wet loses effectiveness and stays damp far longer in a marine climate.
Rusty nails or frost on nail points. Both indicate moisture, though in Washington this can also be condensation from a ventilation problem rather than a roof leak.
Do this on a bright day with the lights off, so daylight through gaps is obvious.
Look in the gutters
Granules accumulating in gutters and at the base of downspouts is the clearest early sign of asphalt roof wear.
Those granules protect the asphalt from ultraviolet degradation. Some loss is normal, particularly on a new roof shedding loose material. Steady accumulation over time, especially with visible bald patches on the roof, means the surface is wearing through.
Look from the ground
You can see more than you expect with binoculars and a slow walk around the house.
Shingles that are lifted, curling at the edges, cupping or missing. Ridge caps out of line. Flashing that has pulled away at chimneys, skylights or wall junctions. Sagging in the roof line, which is structural rather than cosmetic. Debris accumulated in valleys.
Moss growth, and where it is heaviest — usually north-facing slopes and anywhere shaded by trees.
Look at the flashing specifically
Most roof leaks start at flashing rather than in the field of the roof. Chimneys, skylights, vents, dormers and where a roof meets a wall are the places to look first.
Any of these showing gaps, lifted edges, failed sealant or rust deserves attention before the wet season.
Notice the inside signs
Staining on ceilings, particularly recurring after painting. Bubbling paint on an upper-floor ceiling. A musty smell in an upstairs room or closet.
Stains near an exterior wall on an upper floor sometimes indicate a flashing or wall junction issue rather than a roof field leak.
The Washington moss factor
Heavy moss west of the Cascades means the roof is functionally older than its age suggests. Moss lifts shingle edges and holds moisture against the deck, so a fifteen-year-old roof under heavy canopy may be in worse shape than a twenty-year-old roof on an open lot.
If moss coverage is significant, treat the roof’s condition as more advanced than the installation date implies.
When to get a professional look
Anything you found in the attic. Visible flashing problems. Any sagging. A roof approaching 20 years west of the Cascades.
A paid inspection from someone not bidding on the work removes the obvious conflict, and it is worth considering before accepting any replacement recommendation.