---
title: "Flashing and Seam Repair in Ontario | flat-roof-repair.ca"
description: "Flashing and seam repair for flat roofs in Ontario: wall and parapet flashings, curbs, edges and open seams, where most flat roof leaks begin."
url: https://flat-roof-repair.ca/services/flashing-and-seam-repair/
last_updated: 2026-10-23
---

# Flashing and seam repair

The large flat sheet of a roof membrane rarely fails first. The joins do: the seams, the edges and the places where the roof meets a wall.

## What flashing is and why it fails

Flashing is the waterproof detail where the membrane meets something else: a parapet, a chimney, a wall, a curb or the roof edge. Walls and roofs move at different rates with temperature and frost, and that movement pulls on every flashing. The termination bar loosens, sealant dries, and water gets in behind.

Seams fail for related reasons. Heat and cold stretch and shrink the sheet, adhesive ages, and a lap that was never fully bonded lifts at the corner. The pages on [flashing leaks](https://flat-roof-repair.ca/problems/flashing-leaks/) and [open seams](https://flat-roof-repair.ca/problems/open-seams/) show what to look for.

## What we repair

- **Wall and parapet flashing**: Membrane turned up the wall, with a termination bar and sealant, covered by metal counterflashing or cap.
- **Roof edges and drip edge**: Metal edging refastened, replaced or re-lapped under the membrane.
- **Corners and transitions**: Inside and outside corners, where fabricated pieces matter more than sealant.
- **Seam repair**: Cleaned and rejoined by heat-welding on TPO and PVC, by adhesive or splice tape on EPDM, and by patching on bitumen systems.
- **Pitch pockets and penetrations**: Old pitch pockets are replaced with proper boots or collars. See [skylight and penetration repair](https://flat-roof-repair.ca/services/skylight-and-penetration-repair/).

## Repair sequence

- **Identify the failure**: Pull back loose areas, check the substrate and note whether the membrane or the sealant has failed.
- **Clean and prepare**: Seams and flashings only bond to clean, dry, correctly primed surfaces.
- **Rebuild the detail**: New membrane flashing, fresh terminations and, where needed, metal replaced or added.
- **Seal and test**: Check that every edge is bonded, and probe seams for gaps.

## Flashing and seam pricing

| Item | Starting price |
|---|---|
| Flashing repair or replacement | from $500 per repair |
| [Skylight, curb or vent reflashing](https://flat-roof-repair.ca/services/skylight-and-penetration-repair/) | from $350 per opening |
| [Small leak repair (patch, seam or puncture)](https://flat-roof-repair.ca/services/flat-roof-leak-repair/) | from $350 per repair |

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.

Long runs of wall flashing, masonry that needs repointing, and work at height raise the price.

> Many contractors use cold-applied or self-adhered materials where a torch is unsafe near wood framing and other combustibles. We choose the method based on the building, not habit.

## Questions about flashings and seams

**Is caulking a flashing a real repair?**

It is a short-term measure. Sealant dries and cracks with movement. A real repair rebuilds the detail so the sealant is a backup, not the barrier.

**Why does the leak only show in heavy rain?**

Wind-driven rain pushes water behind a loose flashing. In light rain the same gap stays dry.

**Do I need to fix the masonry too?**

If brick or stucco above the flashing is cracked, water can enter behind it. We note it in the report. The masonry repair itself is for a mason.

## Related

- [Flashing leaks](https://flat-roof-repair.ca/problems/flashing-leaks/)
- [Open seams](https://flat-roof-repair.ca/problems/open-seams/)
- [Skylight and penetration repair](https://flat-roof-repair.ca/services/skylight-and-penetration-repair/)
- [TPO roofing](https://flat-roof-repair.ca/materials/tpo-roofing/)

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