Eastern Ontario
Flat roof repair in Cornwall
We repair, replace and maintain flat roofs in Cornwall: houses, garages and additions, condo and apartment buildings, plazas, offices and warehouses. Send photos and a few details for a written quote.
Flat roof services in Cornwall
Much of Cornwall's housing is older, and older houses often have flat roofs over rear additions, porches and garages. Typical signs are a stain on the kitchen ceiling, water at a skylight or a roof with several worn layers. Cornwall has one of the ten heaviest design snow loads of the 40 cities on this site, so drains and parapet flashings get extra attention. We find where the water gets in, fix that spot and tell you how much life the rest of the roof has.
When a roof is past repair, we replace it with EPDM, TPO, PVC or modified bitumen, and fix the drainage so water does not sit on the new membrane. Owners and property managers also book inspections and maintenance visits.
Canal, mills and distribution centres in Cornwall
Cornwall's development accelerated with the Cornwall Canal, built from 1834 to 1842, and its population grew from 7,419 in 1921 to 43,639 in 1961. Courtaulds ran a rayon mill until 1992, and Domtar's paper mill closed in 2006. The Seaway works of the 1950s changed the waterfront and the rail network. Newer industry includes a business park with a Walmart distribution centre of 1,500,000 square feet. Census data shows about 70% of homes were built before 1981.
Many houses date from the mill and post-war years, so flat roofs over rear additions and porches are often found on older brick homes. Downtown, along Pitt Street and Water Street East, there are commercial buildings with flat roofs. Cornwall Square and the surrounding retail carry broad low-slope roofs. The former mill sites and the business park contain some of the largest roofs in the city, which are low-slope by design, and they need regular drainage checks.
Cornwall weather and your flat roof
Ontario's Building Code sets the climate values used to design roofs in each municipality. They show what a flat roof in Cornwall has to handle.
- 2.2 kPaGround snow load (about 46 lb per sq ft)
- 0.4 kPaRain load added to snow (Sr)
- 25 mmRain in a 15-minute storm (design value)
- 103 mmRain in one day, 1-in-50-year storm
- -23 °CJanuary design temperature
- 4,250Heating degree-days per year
- 0.41 kPaHourly wind pressure, 1-in-50-year
That snow load is about 2.4 times the Toronto figure. Snow drifts against parapets, walls and rooftop units, and the weight sits on the roof for weeks. Drains that freeze shut leave meltwater nowhere to go.
A design storm can drop 25 mm of rain in 15 minutes. On a flat roof that water has to reach a drain or scupper quickly, so clear drains and sound drain flashings matter as much as the membrane.
Environment and Climate Change Canada climate normals (1991–2020) record about 198 cm of snowfall a year at the Cornwall station.
Source: Ontario Building Code, Supplementary Standard SB-1, Table 1.2
Homes and buildings in Cornwall
The age and type of buildings shape the flat roofs we see. These are the 2021 Census figures for Cornwall.
- 70%Homes built before 1981
- 10%Homes built since 2001
- 59%Detached and semi-detached houses
- 5%Row houses and townhouses
- 5%Apartments in buildings of 5+ storeys
- 46%Households that rent
About 70% of homes in Cornwall were built before 1981, more than in 34 of the 40 Ontario cities on this site. Older houses often have flat roofs over rear additions, kitchens and porches, sometimes with two or three layers of old roofing on top of each other. Replacing one usually starts with a full tear-off and a look at the wood deck underneath.
46% of households in Cornwall rent. Landlords and property managers can send photos and the tenant's description of the leak, and we reply with the scope and a quote by email. See apartment buildings.
Starting prices in Cornwall
| Item | Starting price |
|---|---|
| Small leak repair (patch, seam or puncture) | from $350 per repair |
| 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 |
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.
See all prices.
Roofs we work on in Cornwall
Nearby cities
Flat roofs in Cornwall: questions
How much does flat roof repair cost in Cornwall?
A small leak repair starts from $350 per repair and a new house flat roof starts from $8,000 per roof. Prices in Cornwall depend on access, layers to remove and the membrane. See pricing.
Why does my flat roof in Cornwall leak in late winter?
Melting snow refreezes at drains and edges overnight, then backs up under seams and flashings during the day. See ice and snow damage.
Do I need a permit to replace a flat roof in Cornwall?
City exemptions include 'Replacing roofing or shingles'; roof-mounted solar PV panels need a permit. That wording is about shingles, so ask how it applies to a flat roof membrane. Rules can change, so confirm with the building department before you start. See re-roofing permits in Ontario.
My Cornwall house is older. Can the flat roof go on over the old one?
Sometimes one new layer can go over one old layer, but on older houses we often find two or three layers already, wet insulation or soft deck boards. Then a full tear-off is the safer choice. See repair or replace.
Do you also work near Cornwall?
Yes, including Ottawa, Kingston, Belleville and the rest of eastern Ontario. See Eastern Ontario.
Leak, damage or an old flat roof?
Send a few details and photos. We reply by email with next steps and a written quote.