Guide
What a flat roof costs in Ontario
Flat roof prices run from a few hundred dollars for a leak repair to five figures for a house roof and much more for a commercial one. This guide shows starting prices and explains what moves the number.
Start with the type of work
Roofers price three different kinds of work, and mixing them up is the main reason quotes look wildly different. A repair fixes one defect and leaves the rest of the roof alone. A coating or restoration adds a new surface over a sound roof. A replacement removes the old layers and installs a new system. Each has its own price logic.
Repairs are priced per visit or per defect because the cost is mostly the call-out, the materials for one patch and the time to find the real source of the leak. Replacements are priced by area, because membrane, insulation and labour grow with the roof.
Repairs and service visits
| 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 |
| Skylight, curb or vent reflashing | from $350 per opening |
| Roof inspection with written photo report (house) | from $250 per roof |
| Maintenance visit (drains, seams, flashings, photos) | from $295 per visit |
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.
Replacement by membrane
| Item | Starting price |
|---|---|
| EPDM roof replacement | from $8 per sq ft |
| TPO roof replacement | from $9 per sq ft |
| PVC roof replacement | from $11 per sq ft |
| Modified bitumen (torch-on or SBS) replacement | from $8 per sq ft |
| Built-up (tar and gravel) roof replacement | from $9 per sq ft |
| Commercial roof replacement | from $8 per sq ft |
The commercial rate applies to large roofs where the area spreads fixed costs. Smaller roofs cost more per square foot.
Whole-roof examples and extras
| Item | Starting price |
|---|---|
| Small flat roof replacement (garage, porch or addition) | from $4,000 per roof |
| House flat roof replacement (about 1,000 sq ft) | from $8,000 per roof |
| Roof coating (restoration) | from $3 per sq ft |
| Tapered insulation (added to a replacement) | from $2 per sq ft |
| Rooftop deck waterproofing membrane | from $22 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.
What moves a quote up or down
Roof size
Bigger roofs cost less per square foot because setup, safety and disposal are spread wider. A garage roof pays the fixed cost on a tiny area.
Number of layers to remove
Each old layer adds tear-off labour and disposal weight. Two or three layers of old tar and gravel make a roof noticeably more expensive to strip.
Wet insulation and rotten deck
Hidden damage found at tear-off is priced per sheet or per area. Ask for the unit price in the quote.
Access and lifting
A ladder, a hoist or a crane. A roof with no side access and no driveway costs more to supply and clear.
Insulation and slope
Adding insulation or a taper to fix ponding costs extra but often solves the root problem. See tapered insulation.
Penetrations and flashings
Every vent, curb, drain and skylight needs its own detail. A roof with many penetrations takes longer than a clean field.
Season
Ontario roofing runs mainly from spring to late fall. Cold weather limits some adhesives and torch-on work, which affects scheduling more than price.
Why quotes differ
Two quotes for the same roof can differ by a third and both be honest. One may include tear-off of every layer and new insulation; the other may cover over the old roof. One may count edge metal, flashings and drains; the other may leave them as extras. The cheaper quote is often the shorter scope. Market research for Ontario found bids for the same scope commonly differing by 30 to 50 per cent, which is why a written scope matters more than the bottom line.
Compare quotes by asking each contractor to list the same items: tear-off, deck repair allowance, insulation, membrane, flashings, edge metal, drains and cleanup. See preparing for a roof quote and hiring a flat roofer.
Repair now or replace later: a cost view
A repair is cheap relative to a new roof, but five repairs in three years add up. If the insulation is wet or the membrane is cracked across the field, repairs will not hold. A useful test: if repairs this year and next year together reach a third of the replacement price, ask for a replacement quote as well. The details are in repair or replace a flat roof.
Coatings can also bridge the gap. A restoration coating, from $3 per sq ft, can extend a sound roof, and coatings commonly last 7 to 20 years, depending on the coating. They do not fix wet insulation or open seams, so a moisture survey comes first.
A worked example, in words
Take a house with a flat roof of about 1,000 square feet, two layers of old roofing and one drain. The quote has to cover removing both layers and the disposal, repairing a few sheets of deck, new insulation, the membrane, edge metal, flashing at the house wall and the drain. Some of those lines are fixed, some scale with area, and the deck repair is an allowance that may go up or down once the roof is open.
Now take a garage roof a quarter of that size. The membrane line shrinks by three-quarters. The setup, the disposal run and the flashing detail do not. That is why the garage price looks high per square foot, and why the large-roof rate in the table is a different number from the small-roof one.
Questions about flat roof cost
Why is a small roof more expensive per square foot?
Setup, disposal and safety costs are about the same on a small roof as on a large one, so each square foot carries more of them.
Should I pick the cheapest membrane?
Not by price alone. Compare the full scope and the service life. See choosing a flat roof material.
Is HST included?
The starting prices on this site are before HST. Your written quote will show the tax.
How do I get a firm number?
Send the roof details through the quote form. For larger or uncertain jobs the firm number follows a look at the roof.
Leak, damage or an old flat roof?
Send a few details and photos. We reply by email with next steps and a written quote.