The most useful roof inspection you can perform yourself does not involve going on the roof. It involves going into the attic, and it takes about twenty minutes. The underside of your roof deck records everything that has happened to it, and unlike the shingle surface, that record is legible to a homeowner.
Choose a bright day. Turn off the attic light and let your eyes adjust for a minute — daylight coming through the deck is the easiest finding to spot and it is invisible with a bulb on. Take a strong flashlight and hold it low, raking the beam along surfaces at a shallow angle rather than pointing it straight on. Raking light throws texture, staining, and moisture into relief in a way direct light flattens out.
Stay on the joists. Step between them and you go through the ceiling. If the attic is fully insulated with no walkway, work from the hatch rather than venturing across, and consider that a finding in itself — limited access limits any inspection, professional ones included.
Look at the decking construction first. Continuous panels mean plywood or OSB. Individual boards with gaps mean skip sheathing, which changes the economics of any future re-roof substantially. This is the single most valuable thing you will learn up there.
Any light coming through where it should not is a hole. Around penetrations, it may indicate a failed boot or flashing. At the ridge or gable, it may be intentional venting. Note the location and correlate it to the roof exterior.
These are water paths, and they are the most useful evidence in the attic. Water runs along the top edge of a rafter and stains the side. Crucially, follow them uphill — the entry point is above where you first see the stain, not below. A stain that continues to the top plate tells you water has been reaching the wall.
The tips of roofing nails protrude through the deck. Rust rings around them mean sustained moisture at that location. Scattered rust in one area suggests a localised leak. Rust across an entire slope suggests something else entirely, which brings us to the important distinction.
This is the diagnostic fork that matters most in Seattle. A leak produces damage radiating from a point — staining along a path, concentrated in one area. Condensation produces damage spread broadly and evenly across a whole slope, typically worst near the ridge and on the north-facing plane, with beading or rust on nail tips throughout rather than in one spot.
If your north slope is uniformly dark and your south slope is clean, you are almost certainly looking at an interior moisture problem, not a roof problem, and roofing work will not fix it.
Chalky or whitish tidemarks on sheathing are where water evaporated and left dissolved minerals behind. They record historic wetting even when everything is currently dry, which is useful for establishing that a repaired leak really was repaired — or was not.
Damp, compressed, or discoloured insulation marks where water has been arriving. Wet insulation also loses most of its thermal value, which makes the ceiling below colder and increases condensation, so it is both symptom and cause.
Exhaust ducts terminating in the attic. Follow the duct from every bathroom fan and from the dryer. It should exit the building through the roof or a wall with a proper hooded termination. A duct ending in open attic space — or connected to a roof vent but fallen off, which is extremely common — is depositing a continuous stream of humid indoor air onto your sheathing. This single defect frequently explains an entire moisture problem.
Blocked soffit intake. Look toward the eaves at the lowest point of the attic. You should be able to see the soffit vents and daylight through them. If insulation has drifted or been blown into that space, the intake side of your ventilation is closed, and no amount of ridge venting will produce airflow. Baffles are the fix and they are inexpensive.
Photograph everything, with something in frame for location reference. Note which slope and roughly how far from the ridge. If you found staining, note whether it is currently damp — touch it — because active and historic damage lead to different conversations.
Then, when contractors come to quote, show them the photographs and ask what they make of it. The quality of that answer is one of the better contractor screening tools available to a homeowner, because it requires reasoning about your specific building rather than reciting a sales sequence.
This post is part of our in-depth coverage of roof replacement in Seattle.
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