Why flat roof leaks are tricky
Water on a flat roof travels. It slips under a cracked seam, runs along the deck, follows a viga or a joist, and drips out wherever it finds a low point in the ceiling. A stain in the living room can start at a canale on the other side of the house. That's why so many flat roof patches fail: someone sealed the spot above the stain instead of the spot where the water gets in.
Common sources
At the edges
Roof-to-parapet corners, cracked parapet caps, loose or rusted canales, and gaps around vigas.
In the field
Worn coating, blisters, split seams, bare spots in gravel, and low areas that pond.
At openings
Skylights, plumbing vents, swamp cooler stands and ducts, chimneys and solar mounts.
Behind the roof
Stucco cracks and failed caps that let water into the wall, then into the ceiling.
How we find it
- Look at the inside first: where the stain is, how big, how fresh, and when it appears (every rain, or only big storms from one direction).
- Walk the roof above and upslope of the stain, checking every seam, corner, canale and opening.
- Probe and moisture-check soft or suspect areas.
- Check the parapets and stucco outside, not just the roof surface.
- When needed, water-test one area at a time to confirm the entry point.
The repair
Once we know the source, the fix is specific: reseal and rebuild a corner, cut out and replace wet foam or felt, reset a canale, flash a skylight, re-seal around a viga, or patch and coat a seam. Every repair is coated or surfaced so it lasts. If the roof has too many failure points to chase one by one, we'll say so and show you why.
After the repair
Let a stained ceiling dry out before painting, and use a stain-blocking primer. If the drywall or plaster is soft or sagging, it should be opened up and dried. See how to find a flat roof leak.
Call us for a free look at your roof. You get photos of what we find and written pricing before any work starts.
Common questions
Can you fix a leak while it's raining?
We can usually stop active water with a temporary seal or tarp, then do the permanent repair when the roof is dry. See emergency flat roof repair.
Why does it only leak in big storms?
Wind-driven rain and heavy monsoon downpours reach places light rain doesn't: parapet caps, high on the walls, and canales that back up.
Will a coating stop my leak?
Not by itself. A coating protects a sound roof. The leak's source has to be repaired first, and any wet material removed.