--- title: "New Flat Roof Installation in Ontario | flat-roof-repair.ca" description: "New flat roofs for additions, garages, porches and new builds in Ontario. Slope, insulation, drains and membrane choices explained, with starting prices." url: https://flat-roof-repair.ca/services/new-flat-roof-installation/ last_updated: 2026-10-23 --- # New flat roof installation A new flat roof is easier to get right than an old one is to fix. The key decisions come before the membrane goes on: slope, drainage, insulation and how the roof meets the wall. ## Where new flat roofs go Most new flat roofs in Ontario cover rear additions, garages and carports, porches, dormer-style extensions and small commercial buildings. Modern designs also use flat roofs on whole houses. Each has the same job: shed water to a defined point, resist snow load, and stay airtight and insulated. Many contractors treat a new flat roof as a framing problem handed over to the roofer. We would rather work with your builder or designer early, because some mistakes cannot be fixed later. For example, a roof framed dead level will pond no matter how good the membrane is. ## What to decide before the roof is built - **Slope**: Frame a slope into the structure, or add it with [tapered insulation](https://flat-roof-repair.ca/services/tapered-insulation/). Water that sits on the roof for days is a warning sign. See [ponding water](https://flat-roof-repair.ca/problems/ponding-water/). - **Drainage**: Interior drains, perimeter scuppers or an edge to a gutter. Each needs a plan for overflow, since a blocked outlet is the usual cause of trouble. See [roof drains and scuppers](https://flat-roof-repair.ca/services/roof-drains-and-scuppers/). - **Insulation and vapour control**: Where in the assembly insulation sits decides whether moisture condenses inside the roof. Your designer or engineer sets the requirement; we build it. - **Membrane**: EPDM, TPO, PVC or modified bitumen, chosen for the building, budget and nearby fire concerns. See [choosing a material](https://flat-roof-repair.ca/guides/choosing-a-flat-roof-material/). - **Penetrations and edges**: Plumbing vents, exhaust vents, skylights and parapet or wall tie-ins should be planned so flashing is simple, not improvised. ## How a new roof is installed - **Plans or site visit**: Send drawings or photos, or we look at the framing before it is covered. - **Assembly proposal**: We describe the layers from the deck up, with options and prices. - **Deck and slope check**: Before membrane goes on we check that the deck is dry, fastened and sloped as designed. - **Installation**: Insulation, membrane, flashings, drains and edge metal, installed in sequence. - **Handover**: Photos of key details, and a note on routine maintenance for the owner. ## Starting prices for new roofs | Item | Starting price | |---|---| | Small flat roof replacement (garage, porch or addition) | from $4,000 per roof | | [TPO roof replacement](https://flat-roof-repair.ca/materials/tpo-roofing/) | from $9 per sq ft | | [EPDM roof replacement](https://flat-roof-repair.ca/materials/epdm-roofing/) | from $8 per sq ft | | [Tapered insulation (added to a replacement)](https://flat-roof-repair.ca/services/tapered-insulation/) | from $2 per sq ft | 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. Small roofs cost more per square foot because setup, flashing and edge work are the same whatever the size. Permit fees and structural work are separate. > Structural, snow load and permit requirements differ by municipality, and a new roof often needs drawings. Check with the local building department. Our [permits guide](https://flat-roof-repair.ca/guides/re-roofing-permits-ontario/) explains what to ask. ## Questions about new flat roofs **How flat is too flat?** A roof should have some slope so water drains, even if it looks level. Designers commonly specify a small slope toward drains. Ask your designer for the figure used on your project. **Can you build the structure too?** We install the roof system on a deck your builder or carpenter provides. We do not offer framing or general construction. **Is a flat roof right for my garage addition?** Often yes, since it is simple and affordable. See [garages and additions](https://flat-roof-repair.ca/property-types/garages-and-additions/) for the points to settle first, such as where the water goes. ## Related - [Flat roofs on garages and additions](https://flat-roof-repair.ca/property-types/garages-and-additions/) - [Tapered insulation](https://flat-roof-repair.ca/services/tapered-insulation/) - [TPO roofing](https://flat-roof-repair.ca/materials/tpo-roofing/) - [Re-roofing permits in Ontario](https://flat-roof-repair.ca/guides/re-roofing-permits-ontario/) --- Get a quote: https://flat-roof-repair.ca/request-a-quote/ ยท Email: info@flat-roof-repair.ca