--- title: "Flat Roof Leak Repair in Ontario | flat-roof-repair.ca" description: "Flat roof leak repair across Ontario: we trace water to its real entry point and fix that spot. Houses, condos and commercial roofs. Starting prices listed." url: https://flat-roof-repair.ca/services/flat-roof-leak-repair/ last_updated: 2026-10-23 --- # 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. ## 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](https://flat-roof-repair.ca/problems/flashing-leaks/). - **Seams**: Welded, glued or lapped seams can separate after many seasons of heat and frost. See [open seams](https://flat-roof-repair.ca/problems/open-seams/). - **Penetrations**: Vents, pipes, skylight curbs and rooftop units each have a seal that can fail. See [skylight and penetration repair](https://flat-roof-repair.ca/services/skylight-and-penetration-repair/). - **Drains and scuppers**: A blocked drain sends water to places the roof was never meant to hold. See [clogged drains](https://flat-roof-repair.ca/problems/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](https://flat-roof-repair.ca/problems/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)](https://flat-roof-repair.ca/pricing/) | from $350 per repair | | [Flashing repair or replacement](https://flat-roof-repair.ca/services/flashing-and-seam-repair/) | from $500 per repair | | [Roof drain or scupper repair](https://flat-roof-repair.ca/services/roof-drains-and-scuppers/) | 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. > If the same spot keeps leaking after repairs, or the roof is soft underfoot, the insulation is probably saturated. A patch will not hold, and the [repair or replace guide](https://flat-roof-repair.ca/guides/repair-or-replace-flat-roof/) shows when to step up. ## 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](https://flat-roof-repair.ca/guides/finding-a-flat-roof-leak/) 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](https://flat-roof-repair.ca/guides/flat-roof-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](https://flat-roof-repair.ca/problems/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. ## Related - [Flat roof repair](https://flat-roof-repair.ca/services/flat-roof-repair/) - [Ceiling water stains](https://flat-roof-repair.ca/problems/ceiling-water-stains/) - [Finding a flat roof leak](https://flat-roof-repair.ca/guides/finding-a-flat-roof-leak/) - [Emergency flat roof repair](https://flat-roof-repair.ca/services/emergency-flat-roof-repair/) --- Get a quote: https://flat-roof-repair.ca/request-a-quote/ ยท Email: info@flat-roof-repair.ca