Protect the inside, find out what is above the wet spot, and work out which trade you are actually calling. In that order.
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Roof leaks: where the water actually gets in
A roof that leaks is rarely a roof that has failed. It is almost always one joint, one penetration or one flashing detail that has stopped doing its job, and the pattern of when the water shows up narrows it down fast.
Roofs almost never leak in the middle
Here is the single most useful thing to know about roof leaks, and it is the opposite of what most people assume: a roof almost never leaks through the middle of a slope. Water gets in where the roof stops being a simple plane — a chimney, a skylight, a plumbing vent, a valley where two slopes meet, the junction where a roof runs into a wall. Those are the places where two materials have to be persuaded to work together, and those are the places that fail.
That matters because it changes what you are looking for. You are not hunting for a hole. You are asking what is above the wet spot. Water that enters at a chimney can run down a rafter for eight or ten feet before it drops, so the stain on the ceiling is a poor guide to the entry point and the thing directly above it in the attic is a much better one.
The second most useful thing is when it appears. A leak that shows up only in driving rain with wind behind it behaves differently from one that appears in every shower, and both behave differently from water that turns up on a cold clear morning with no rain for a week — which is very often not a leak at all but condensation forming in the attic and dripping back down. Telling those two apart is the single question this site gets asked most, and it is why the Find the leak tool starts there.
This section works through the leak by location: valleys, vents, chimneys, dormers, the wall junction, flat and low-slope sections, and the specific case of a roof that has just been replaced and is leaking anyway. It also covers the first hour — what to do with the water inside while you sort out the roof.
What you will not find here is a set of steps for climbing up and fixing it. That is deliberate and we explain why on every page: falls from roofs are one of the most common serious home-repair injuries in the country, the evidence you need is visible from the ground and from inside the attic, and a wet roof deck is a genuinely dangerous place to stand. We also do not publish prices, and we do not give insurance advice.
Roof leaks guides
A valley carries more water than any other part of the roof, and it carries it fast. That is why it wears out first and why debris there matters.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.