--- title: "Flat Roofs on Houses in Ontario | flat-roof-repair.ca" description: "Flat roof repair and replacement for Ontario houses: rear additions, porch roofs and whole-house flat roofs, with materials, access and what to prepare." url: https://flat-roof-repair.ca/property-types/houses/ last_updated: 2026-10-23 --- # Flat roofs on houses Most Ontario houses with a flat roof have one over a rear kitchen, a family-room addition, a porch or a dormer. The roof is small, but it sits directly above a heated room. ## What is different about a house roof A house flat roof is almost always a wood-frame roof: joists, plywood or board sheathing, insulation and a membrane. Wood reacts to trapped moisture, so a small leak that goes unnoticed for two winters can mean wet insulation and soft sheathing, not just a patch. Older homes in Toronto, Hamilton and Ottawa often have a flat section built decades ago with little or no slope and a thin layer of insulation. The roof is also close to people. You hear the work, you smell the adhesive or the torch, and the ceiling under the roof is the one that shows a stain first. That is why a house job is planned around the family: which room is below, where the ladder goes and whether the dog can be in the yard. ## Problems we see most on houses - **Ponding at the back of an addition**: A slight dip or too little slope leaves water sitting. See [ponding water](https://flat-roof-repair.ca/problems/ponding-water/). - **Failed flashing at the house wall**: The joint where the flat roof meets brick or siding is the most common leak point. See [flashing leaks](https://flat-roof-repair.ca/problems/flashing-leaks/). - **Ceiling stains below**: The stain is often several feet from the actual opening. See [ceiling water stains](https://flat-roof-repair.ca/problems/ceiling-water-stains/). - **Blocked scuppers and small drains**: Leaves from nearby trees fill small outlets and the roof holds water. See [clogged drains](https://flat-roof-repair.ca/problems/clogged-drains/). - **Cracked old tar and gravel or roll roofing**: Old materials dry out after many freeze–thaw cycles. See [cracks and alligatoring](https://flat-roof-repair.ca/problems/cracks-and-alligatoring/). ## Materials that usually suit a house - **EPDM**: A single rubber sheet with few seams, well suited to small, simple roofs. 20 to 30 years. See [EPDM roofing](https://flat-roof-repair.ca/materials/epdm-roofing/). - **Modified bitumen**: A multi-layer system that handles foot traffic and is easy to patch. Many contractors use cold-applied or self-adhered versions where a torch is unsafe beside wood framing. See [modified bitumen](https://flat-roof-repair.ca/materials/modified-bitumen-roofing/). - **TPO or PVC**: Heat-welded white membranes; useful when the roof is sunny and the room below overheats. See [TPO](https://flat-roof-repair.ca/materials/tpo-roofing/) and [PVC](https://flat-roof-repair.ca/materials/pvc-roofing/). ## How a house job is planned - **Look and measure**: We look at the roof, the ceiling below and the access at the side or back of the house. - **Decide repair or replace**: A local repair is reasonable if the layers below are dry. Wet insulation points to replacement. See [repair or replace](https://flat-roof-repair.ca/guides/repair-or-replace-flat-roof/). - **Plan the day**: Most house roofs are a one- to three-day job in dry weather. Torch-on work needs a clear plan for fire safety; cold-applied systems avoid the open flame. - **Protect the property**: Tarps over gardens and decks, a dumpster or a tear-off chute, and a magnet sweep of the yard at the end. ## What to prepare as the owner - **Photos**: The roof from a window or ladder, the ceiling stain, and the wall where roof and house meet. - **Rough size**: Length and width of the roof in feet or metres. A tape measure on the ground is enough. - **Access**: Where a ladder or a small lift can stand, and whether a dumpster fits in the driveway. - **History**: Roughly how old the roof is, whether there is more than one layer, and where it has leaked before. See [preparing for a roof quote](https://flat-roof-repair.ca/guides/preparing-for-a-roof-quote/). ## Starting prices for houses | Item | Starting price | |---|---| | [Small leak repair (patch, seam or puncture)](https://flat-roof-repair.ca/services/flat-roof-leak-repair/) | from $350 per repair | | [Small flat roof replacement (garage, porch or addition)](https://flat-roof-repair.ca/services/flat-roof-replacement/) | from $4,000 per roof | | [House flat roof replacement (about 1,000 sq ft)](https://flat-roof-repair.ca/services/flat-roof-replacement/) | from $8,000 per roof | 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. Prices per square foot for each membrane are on the [pricing page](https://flat-roof-repair.ca/pricing/). ## Questions from house owners **Do I need to move out while the roof is done?** No. You stay in the house. Expect noise from tear-off and some smell from adhesives or heat-welding, so plan to keep windows near the roof closed. **My flat roof is over a kitchen. Is there anything to protect inside?** Move items off the ceiling area and cover cabinets near it. Tear-off can shake dust loose from old ceilings. **Can a new flat roof have a skylight or a deck on it?** Yes, but both need proper curbs, flashing and a protected membrane. See [skylight repair](https://flat-roof-repair.ca/services/skylight-and-penetration-repair/) and [rooftop deck waterproofing](https://flat-roof-repair.ca/services/rooftop-deck-waterproofing/). ## Related - [Flat roofs on garages and additions](https://flat-roof-repair.ca/property-types/garages-and-additions/) - [Flat roof replacement](https://flat-roof-repair.ca/services/flat-roof-replacement/) - [EPDM roofing](https://flat-roof-repair.ca/materials/epdm-roofing/) - [Repair or replace a flat roof?](https://flat-roof-repair.ca/guides/repair-or-replace-flat-roof/) --- Get a quote: https://flat-roof-repair.ca/request-a-quote/ · Email: info@flat-roof-repair.ca