Find the entry point, then fix it
Flat roof leak repair
On a flat roof the stain on your ceiling is rarely under the hole. Water runs along the deck and the insulation before it drips, so the real work is tracing it back.
- Tracing, not guessing
- Houses and commercial
- Starting price listed
Why leaks on flat roofs are hard to place
A pitched roof sheds water in one direction, so a drip usually sits below the damage. A flat roof holds water, and a membrane over insulation lets water slide sideways between the layers. A drip can show up in a kitchen while the opening sits across the building, near a parapet wall.
That is why a quick dab of sealant over the stain so often fails by the next storm. A repair only lasts if it is made where the water goes in.
Where the water usually gets in
Flashings at walls and edges
Where the membrane turns up a wall or over a parapet, the termination can open with movement. See flashing leaks.
Seams
Welded, glued or lapped seams can separate after many seasons of heat and frost. See open seams.
Penetrations
Vents, pipes, skylight curbs and rooftop units each have a seal that can fail. See skylight and penetration repair.
Drains and scuppers
A blocked drain sends water to places the roof was never meant to hold. See clogged drains.
Punctures and wear
Foot traffic, fallen branches and tool drops cut or crush the membrane, and old membranes crack. See cracks and alligatoring.
How we repair a leak
Your description
Where the water shows, when (rain, melt, wind-driven rain) and what you have already tried.
Roof walk
We look at drains, flashings, seams, penetrations and low spots, and test suspect areas where we safely can.
Opening up if needed
Where wet insulation is suspected we cut a small test area to see how far the moisture has travelled.
Repair at the source
New flashing, a patch, a seam repair or a section of membrane, matched to what is already on the roof.
Photos and notes
You get photos of the entry point and the repair, and a note on anything else that will need attention.
What a leak repair costs
| Item | Starting price |
|---|---|
| Small leak repair (patch, seam or puncture) | from $350 per repair |
| Flashing repair or replacement | from $500 per repair |
| Roof drain or scupper repair | from $800 per drain |
Starting prices in CAD before 13% HST, based on typical Ontario contractor rates (mostly Toronto and the GTA). The final price depends on roof size, access, the layers to remove, the membrane, drains and flashings, and is confirmed in your written quote.
A single accessible entry point is the low end. Several leak points, wet insulation or hard roof access raise the price, and we will tell you before work starts.
Help us find it faster
Photos of the stain
Wide and close-up, with a note of when it first showed.
Weather pattern
Does it only leak in wind-driven rain, only in spring melt, or after every storm?
Roof type
EPDM, TPO, modified bitumen, tar and gravel, or unknown. A photo of the top surface is enough.
Access
Roof hatch, ladder or interior stairs, and whether a neighbour's property is involved.
Questions about leak repair
Why is my ceiling wet when the roof looks fine?
Water travels. It can enter at a wall flashing and run along the deck before it finds a gap in the ceiling. The leak-finding guide shows how to narrow it down.
Can a leak be repaired in winter?
Often yes, with cold-applied materials, but adhesion is weaker in deep frost and snow must be cleared first. We may recommend a temporary fix and a permanent one in milder weather. See flat roofs in winter.
Will the ceiling stain disappear?
The roof repair stops new water. The stain and any damaged drywall are interior work. See ceiling water stains for what to check inside.
How do I know the leak is really fixed?
Wait for the next heavy rain or thaw and check the same spot. Note the date of the repair so any new stain is easy to compare.
Leak, damage or an old flat roof?
Send a few details and photos. We reply by email with next steps and a written quote.