Short answer: start in the attic during or right after rain with a flashlight, find the wet spot on the decking, then trace uphill. Water travels along rafters and across decking, so the entry point is almost always higher and often several feet away from the stain below.

Why the stain is not the leak

Water enters at a penetration, lands on the decking, follows the slope or a rafter, crosses to another part of the attic and finally drops through the ceiling. We have traced leaks that entered fifteen feet from where they appeared inside.

That is why a patch applied directly above the stain usually fails. The job is finding the entry, not sealing the exit.

Tracing it from the attic

  1. Go up during or just after rain with a good flashlight. Active water narrows the search enormously.
  2. Find the wet decking or the drip and follow the wetness uphill along the rafter or sheathing.
  3. Look for the highest wet point. That is usually at or near the entry.
  4. Check what is above it on the roof: a vent, a valley, a chimney, a skylight, a wall termination.
  5. Mark it. A nail pushed through from inside, or chalk, so you can find it again when dry.

The usual entry points, in order

  1. Pipe boots. The rubber collar around plumbing vents cracks at 8 to 12 years in Texas UV. This is the single most common non storm leak we find.
  2. Chimney flashing. Especially on older homes with masonry chimneys. See our chimney guide.
  3. Valleys packed with debris, which backs water sideways under the laps.
  4. Roof to wall transitions missing kick-out flashing.
  5. Skylights with aged seals or reused flashing.
  6. Wind damaged shingles whose seal strips broke months ago.
  7. Gutter overflow pushing water back under the roof edge.

Rule out condensation first

If moisture appears after a cold clear night with no recent rain, that is condensation rather than a leak, and the fix is ventilation and air sealing. Our condensation guide covers how to tell them apart.

When to stop

Do not climb onto the roof, particularly when wet. Do not cut into a ceiling to investigate. Do not run a hose on the roof while someone is inside unless you are methodical about it, because flooding the whole roof tells you nothing about where the water got in.

If you cannot find it from the attic, or the attic is inaccessible, that is the point to call someone with the equipment and the experience.

We diagnose leaks for free and tell you honestly whether it is a repair or something larger. Get in touch or call (210) 245-4125. For active intrusion see emergency roof repair.