A lumbered slope framed over a flat roof deck to move water toward the drains, with a two-ply system installed over it.
Lumbered Slope Build and Two-Ply System, Toronto
Open Lumbered Slope Build and Two-Ply System, Toronto
Flat roofing in Thornhill, York Region
Thornhill Flat Roof Repair, Installation, and Replacement
Flat and low-slope roofing in Thornhill, York Region. Free written quotes, manufacturer and workmanship warranties, and an emergency line that answers at night.
What you get from Flat Roofs Toronto
24/7 Emergency Response
Leaks do not wait for business hours.
Free No-Obligation Quotes
Scope, system and number, in writing, first.
Manufacturer & Workmanship Warranties
The materials and the installation are both covered.
Flat Roofs Only
Low-slope work is the whole business, not a sideline.
How Flat Roofs Age in Thornhill
Thornhill is older than the subdivisions further north, and the roofs show it. Postwar bungalows and split levels here have picked up rear additions, family room wings and enclosed porches, nearly all finished with small low slope decks tied into the original sloped roof. Many are already on a second or third membrane. Newer infill and full rebuilds add modern flat roofed sections along the same streets. On the commercial side, strip plazas and low rise office buildings line the Yonge Street spine, carrying rooftop mechanical and interior drains. Tall trees shade most of the older streets, and their debris is the most reliable cause of a blocked outlet anywhere in the area.
What We Do on Thornhill Roofs
In Thornhill we replace and repair addition and garage decks, rebuild the flashing where a flat section meets the sloped roof, reflash and replace leaking skylights, clear and rebuild drains and scuppers, re roof plaza and low rise commercial fields in stages, and take emergency flat roof calls 24/7.
Where Thornhill Sits in Our Service Area
The plan opens on this part of the GTA. Every city we cover in the region is in the legend beside it.
Select a region on the plan
Systems That Suit Thornhill
Small additions and rear wings in Thornhill take SBS modified bitumen in two plies, or fully adhered EPDM. Skylight heavy decks benefit from liquid applied detailing around the curbs. Plaza and low rise commercial fields suit TPO, or PVC under kitchen exhaust. Compare every flat roofing system.
Two Ply
Modified Bitumen
Torch-applied or self-adhered SBS in two plies, with a granule-surfaced cap. The default on Toronto houses because it handles tight perimeters, curbs and wall terminations without a wide sheet.
- 15 to 20 year service life
- Redundant second ply
- Repairs patch cleanly
Torch Free
Cold-Ply
The same two-ply build assembled in cold adhesive rather than with an open flame. It is what we specify over occupied buildings, beside vinyl siding and anywhere a torch is not welcome.
- No open flame on the roof
- Low odour on occupied buildings
- Granule-surfaced cap
Single Ply
TPO and PVC
Hot-air welded thermoplastic sheet, laid in wide rolls with far fewer seams. It suits large commercial fields, and the reflective white surface keeps a warehouse roof cooler through a Toronto summer.
- Welded rather than glued seams
- Reflective white surface
- Fast over large areas
Rubber
EPDM
A synthetic rubber membrane that stays flexible through freeze thaw movement and takes ponding better than most. Common on garages, additions and small commercial decks.
- Flexible in cold weather
- Tolerates standing water
- Simple to detail and repair
Local Considerations in Thornhill
The conditions that decide how long a roof here lasts, and what we detail differently because of them.
- Meltwater and shed snow from the sloped main roof land on the addition deck below, and the ice that builds at that step is what drives water back under the membrane.
- Old, tall trees over the established streets drop leaves and seed into scuppers and drain baskets, and a deck with a single outlet ponds within hours once it plugs.
- Skylights and light wells are common on Thornhill rear additions, and their curbs and counterflashing leak far more often than the field membrane surrounding them.
Recent Flat Roofing Projects
Real jobs photographed on site by the crews who did them.
Flat Roof Application Detail, Toronto
A detail from a flat roof membrane application, showing the finished surface of the system.
Attic Inspection and Blown-In Insulation, Toronto
Inspection of a flat roof attic space followed by blown-in insulation. The cavity is checked before any insulation is added.
Flat Roofing Advice
What we have written about keeping a low-slope roof watertight in this climate.
Flat Roofing in Richmond Hill: Best Systems for 2026
A practical 2026 guide to flat roofing in Richmond Hill: best membrane systems, real installed costs, Ontario Building Code insulation and drainage rules.
Commercial Flat Roofing in Markham: 2026 Guide
Commercial flat roofing in Markham: 2026 costs, membrane systems, drainage and Ontario Building Code rules, permits and maintenance for GTA building owners.
Commercial Flat Roofing in Vaughan: An Owner Guide
Commercial flat roofing Vaughan guide: 2026 costs, TPO, EPDM and modified bitumen options, drainage, permits and maintenance for York Region building owners.
Thornhill Flat Roofing Questions
Straight answers to what people ask us about a roof on this street.
The skylight on my Thornhill addition leaks. Is the skylight or the roof at fault?
Usually the curb and flashing rather than the glazing. On Thornhill additions the skylight sits on a wood curb, the membrane turns up that curb, and a metal counterflashing caps it. When the upturn is too short or the counterflashing has loosened, water enters at the head and runs down inside. We rebuild the curb detail and only replace the unit when its own seal has failed.
How often should a flat roof be inspected?
Twice a year suits most Thornhill roofs: in spring after the thaw, and in autumn once the leaves are down. The inspection covers drains and scuppers, seams and laps, flashing at walls and curbs, and the transition to the sloped roof. Small problems caught then cost a fraction of what the same problem costs after a winter of water sitting on it.
What causes the leak where my flat addition meets the main roof?
That step is the hardest working detail on a Thornhill house. Snow slides down onto the flat deck, ice builds along the step, and meltwater ends up sitting higher than the membrane edge. If the upturn behind the siding or shingles is too short, or was never counterflashed, water gets in behind it. The repair is rebuilding that junction properly, not another bead of sealant.
Do you re roof plazas and low rise buildings in Thornhill?
Yes, commercial and residential both. Thornhill plaza and low rise office roofs get re roofed in sections so tenants and staff stay open, with interior protection under any area opened up and each section dried in daily. Rooftop units, exhaust curbs and interior drains are rebuilt as part of the scope rather than reused blind.
Nearby Areas We Also Cover
Flat roofing in the streets either side of Thornhill:
Richmond Hill • Markham • Vaughan • Concord • All of York Region
Google Reviews
Reviews From Across the GTA
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Get a Free Flat Roof Quote in Thornhill
Free, no-obligation quotes across Thornhill and the rest of York Region, and a 24/7 emergency line on (647) 333-3528.