Ice Dam Repair on a Commercial Roof: Remove, Repair, Prevent
How ice dams form on flat and low-slope roofs, how the ice comes off safely, and how to stop it coming back.
Call 1-833-775-7663 Oakville head office · Roof repair for commercial, industrial and institutional buildings across Ontario
Karol Rajkowski
Vice President, OYH Roofing
Published October 18, 2026 · 13 min read
Short answer
Ice dam repair on a commercial roof is three jobs: getting the ice off without cutting the membrane, repairing the flashings, edge metal, gutters or membrane it damaged, and fixing why it formed. On most commercial buildings, ice dams start at cold roof edges, gutters and drains, where meltwater from heat lost through the roof refreezes.
What is an ice dam on a commercial roof?
A ridge of ice that forms where meltwater runs onto a colder part of the roof and freezes, so the water behind it has nowhere to go. The National Research Council of Canada (NRC) describes four conditions that make one: snow on the roof, outside air below freezing, heat from the building or the sun to melt the snow, and a cold edge where the water can freeze.
Flat roofs get them too. The installation manual for RAYCHEM IceStop, a roof de-icing cable, says ice dams may occur on flat roofs at the edge flashing and at drains. On a poorly drained flat roof, NRC adds, meltwater pools and freezes in a sheet that is hard to see. The sheet rarely harms the roofing, but water that freezes in cracks, wrinkles or holes can tear a membrane apart.
| Where | Why ice builds there | What it can damage |
|---|---|---|
| Edge flashing and gutters on low-slope roofs | Edge metal and gutters sit outside the heated building and stay colder than the roof | Edge metal, gutters, downspouts, the wall below |
| Roof drains and scuppers | Meltwater runs to the outlet and freezes in a cold strainer, sump or scupper | Membrane and flashing at the drain; water backs up and ponds |
| Mansards, canopies and sloped sections | The overhang is not warmed from below, so water from the warmer roof above freezes there | Shingles or metal panels, soffits, walkways and doors below |
| Lower roofs beside taller walls or roofs | Snow drifts and slides onto them, and meltwater drains onto them from above | Extra ice load; wall and parapet flashings |
| Around exhaust fans and warm equipment | Heat from fans and units melts snow that refreezes nearby | Flashings at curbs and penetrations |
| Deep or uneven snow in the sun | Thick snow insulates the roof, and sun melts it unevenly | Anywhere the meltwater meets a cold spot |
Heat drives all of it. NRC names heat lost through the roof as the main reason snow melts in freezing weather, with the sun second, and estimated that on insulated buildings melting can start at about -9°C outside. An IIBEC paper (U.S., 2010) notes that a roof can meet the energy code and still form ice dams.
Why do ice dams form so often in the GTA?
Because GTA winters keep crossing 0°C. On a freeze-thaw day, snow melts in the afternoon and the water refreezes at night, which is how ice dams grow. Environment and Climate Change Canada's 1991 to 2020 climate normals work out to about 81 such days a year at Toronto Pearson and about 84 at Hamilton's airport, with March the busiest month at every station.
| Month | Toronto Pearson | Toronto (City) | Hamilton (airport) |
|---|---|---|---|
| November | 13.1 | 7.3 | 13.9 |
| December | 14.9 | 11.0 | 14.7 |
| January | 10.6 | 10.0 | 9.8 |
| February | 12.7 | 11.3 | 11.6 |
| March | 17.1 | 12.9 | 17.1 |
| April | 8.9 | 4.2 | 11.0 |
| Whole year | 81.1 | 57.2 | 83.8 |
Downtown Toronto, close to the lake, averages fewer freeze-thaw days, but a building's own heat loss can melt the snow on its roof on days that stay below freezing. Toronto Pearson also averages 114.5 cm of snow a year, and March has the most freeze-thaw days at all three stations, so ice dams can keep forming well after the coldest weeks. Our winter preparation guide covers what to do before the first snow.
When should you worry about an ice dam on a commercial roof?
As soon as ice is building at a roof edge, gutter, scupper or downspout, or water shows up inside during a thaw. NRC warned that falling icicles can be a significant hazard to people and property, so ice over a door, walkway or parking area is urgent even when nothing is leaking yet.
- Icicles and ice ridges at gutters, scuppers, edge metal or canopy edges.
- Water inside during a thaw, often along exterior walls or at top-floor ceilings near the perimeter.
- Ice at downspout outlets or over drains: water is not leaving the roof. Our drainage repair guide explains frozen drains.
- Gutters pulling away or edge metal bent by ice.
- Twisting, bending or cracking in the structure. Ontario's Ministry of Labour advises having a professional engineer assess it; see our snow load guide.
The safe first steps happen on the ground and inside: keep people out of the area below, move stock away from drips, contain the water, photograph the damage for your insurer, and call a roofer. CRCA, the Canadian Roofing Contractors Association, tells owners to stay off the roof and to use only qualified, insured roofing contractors.
How is ice dam repair done on a commercial roof?
In six steps, and the order matters: make the area safe, open a path for the water, then repair the damage and fix the cause. Ice dam repair that stops once the ice is gone leaves the damage under it and the reason it formed.
| Step | What happens | Why |
|---|---|---|
| 1. Make the area safe | Fence off the area below; keep staff off the roof; contain water inside | Falling ice and hidden roof edges are the main hazards; the Ministry of Labour says snow drop areas should be secured |
| 2. Find the ice and the cause | A roofer checks the edges, gutters and drains, and the inside of the building | The fix depends on whether heat loss, drainage or drifting snow made the ice dam |
| 3. Open a path for the water | Ice cleared from drains, scuppers and gutters; snow removed with plastic tools | CRCA names steam for clearing ice at drains; makers ban metal tools on the membrane |
| 4. Repair the damage | Flashings, edge metal, gutters and membrane repaired to the maker's details | Patches extend at least 150 mm past the defect (CRCA, IKO) |
| 5. Check for wet insulation | Moisture survey, confirmed with core samples | CRCA: remove and replace wet insulation. NRCA: infrared scans need cores |
| 6. Fix the cause | Air sealing and insulation, drainage repairs, heat cable where it fits | NRCA: ice dams start with heat and air leaking from the building |
Steps 1 to 3 are often urgent. Permanent repairs can sometimes wait for a dry, milder day, because many membrane adhesives have minimum application temperatures, listed in our winter preparation guide.
How are ice dams removed without damaging the roof?
With heat and plastic, not force. CRCA's bulletin on ice on roofs names steam, or careful chipping, for clearing ice from drains, and the membrane makers we checked rule out the tools most people reach for. Natural Resources Canada warns that attacking ice dams with an axe or ice pick damages the roof surface.
| Method | What the sources say | Verdict |
|---|---|---|
| Steam | CRCA names steam for clearing ice at drains; no roofing maker we found publishes a pressure or temperature limit | For trained crews; ask the membrane maker for its limits |
| Plastic shovel, rubber-edged shovel, soft broom | IKO: only plastic shovels on flat roofs. Elevate: a rubber-edged shovel or soft broom, leaving a thin layer of snow | The accepted tools for snow |
| Metal shovels, rakes, picks and axes | SOPREMA: metal shovels and rakes should not be used. Natural Resources Canada: axes and ice picks damage the roof | Not on a membrane roof |
| Snow blowers and other machines | Elevate: not under any circumstances. IKO: mechanical equipment may damage roofing materials | Not on a membrane roof |
| High-pressure water | SOPREMA: not without its written approval | Avoid |
| Rock salt and calcium chloride | CRCA: avoid both; they corrode metal flashings. NRCA: de-icing salts are corrosive. Elevate: calcium chloride is less risky, near drains only, rinsed off. Carlisle: EPDM resists both chemically | The sources disagree; ask the membrane maker first |
Figures often quoted online for ice dam steamers, such as staying under 300 psi, come from equipment makers and contractor videos, not from roofing makers or CRCA. The aim is to open a path so meltwater can reach a drain, scupper or gutter, not to strip the roof bare; Elevate even asks for a thin layer of snow to be left on the membrane.
Snow also hides skylights and hatches. Ontario's Ministry of Labour reports a roofing worker who sat on a snow-covered skylight that gave way, and IHSA has counted 10 deaths from falls through skylights since 2002. Workers on a roof must use fall-arrest or travel-restraint equipment.
What damage do ice dams leave on a commercial roof?
Most of it is at the edges and inside layers you cannot see. Water held back by an ice dam finds open laps, cracked flashings and gaps at the edge metal, and when it freezes there, NRC says, it can tear the membrane. The weight of the ice also damages eaves, gutters and edges.
- Edge metal and gutters. Bent or split edge metal, gutters pulled off their brackets, crushed downspouts. CRCA notes that edge metal tends to split at or near the joints.
- Flashings. Flashings at walls, curbs and parapets opened by ice or overwhelmed by a fast thaw. See our roof flashing repair guide.
- Membrane. Splits, opened seams and cuts, many from the ice removal itself; Elevate lists snow shovel damage among common causes of roof damage. See our membrane roof repair guide.
- Wet insulation. Water under the membrane soaks the insulation, which then insulates poorly.
- Inside the building. Stained ceilings, wet walls and damaged contents, which IKO's roof warranty, for one, excludes.
Repairs follow the membrane maker's details. CRCA's reference manual says to find how far the moisture has spread, open the membrane to inspect the insulation and deck, replace wet insulation, and make the patch at least 150 mm larger than the defect on every side. NRCA notes that infrared cameras see temperature differences, not moisture, so suspect areas are confirmed with core samples. Our leak detection guide explains how leaks are traced.
Ice building up on your roof?
Keep people clear of the area below and stay off the roof. Call us and we will look at what can be done safely now and what should wait for a proper repair.
Call 1-833-775-7663Request an assessmentHow do you stop ice dams from coming back?
By keeping heat in the building and getting water off the roof. NRCA (U.S.) says ice dams are caused mainly by heat leaking through poorly built thermal and air barriers. Ontario's Building Code makes the same point in its own terms: on larger buildings, insulation and air barriers must be designed to limit ice damming on sloped roofs.
- Air sealing and insulation at the edge. Building Science Digest 135 names thin insulation, thermal bridging and air leaking into the roof as the causes. The fix belongs in a re-roof or an envelope repair, not a patch; our flat roofing material guide covers insulation for cold roofs.
- Drainage that works in winter. Strainers, scuppers and gutters cleared in the fall, and outlets that stay open. See our guide to ponding water on a flat roof.
- Ventilation for sloped sections. On small buildings, the Building Code requires attic and roof spaces above the insulation to be vented unless shown to be unnecessary, but exempts the lower part of a mansard. Building Science Digest 135 calls it bad practice to try to ventilate away large air leaks, so seal them first.
- Eave protection on shingled sections. On small (Part 9) buildings with shingle, shake or tile roofs, the Building Code requires eave protection from the edge at least 900 mm up the slope, to a line at least 300 mm inside the inner face of the wall. CMHC notes that these membranes do not stop ice dams; they keep the water out when one forms.
Heat cable is a partial answer. RAYCHEM's IceStop manual says its cable is designed to remove meltwater, not accumulated snow; on flat roofs it runs around the perimeter and continues through gutters and downspouts, with ground-fault protection on each circuit. NRCA (U.S.) advises against heat cables on roofs and points to the heat and air leaks instead. In Ontario, heat cable is electrical work: the Electrical Safety Authority (ESA) says anyone hired to do it must be a licensed electrical contractor, who files a notification before or within 48 hours of starting. For heat cable at drains, see our drainage repair guide.
What do Ontario's rules say about ice on a commercial roof?
Owners must keep roof snow and ice from endangering people, and crews who clear it must be protected from falls. Under the Occupiers' Liability Act, an occupier must take reasonable care that people on the premises are reasonably safe. The Municipal Act lets municipalities require owners to remove snow and ice from roofs, and several GTA by-laws do.
| Municipality | What the by-law requires | By-law |
|---|---|---|
| Toronto | Where roof snow or ice may fall on a street, sidewalk or lane and becomes dangerous, remove it immediately, and warn the public while removing it | Municipal Code Ch. 719, s. 719-4 |
| Toronto | Roofs free of leaks, unsafe objects and dangerous accumulations of ice and snow | Municipal Code Ch. 629, s. 629-20A |
| Mississauga | Roofs weather-tight and free of loose objects and excessive ice and snow; eavestroughs and drainpipes in working order | By-law 0654-1998, ss. 10 and 37 |
| Brampton | Where snow or ice is likely to fall on the street, remove it forthwith, with adequate warning to people passing | By-law 242-76, ss. 2 and 3 |
| Markham | Remove roof snow and ice that is a hazard to the normal use of walkways, driveways, parking areas and entrances | By-law 2017-27, s. 4.14 |
| Oakville | No roof snow clause; roofs must be free of conditions that may create a health or accident hazard | By-law 2023-074, s. 13(4)(b) |
- Workers. Ontario's Ministry of Labour says workers on a roof must use fall-arrest or travel-restraint equipment, and that areas where roof snow is dumped should be secured. The construction regulation, O. Reg. 213/91, also calls for a fence along a public way where work may endanger people using it.
- Building design. The Building Code requires provision to minimize hazardous conditions where water, snow or ice can accumulate on a building (Part 5), and covers extra ice loads from meltwater and sliding snow (Part 4). Ask your designer how these apply to a new canopy, an addition or a re-roof.
- Insurance and warranty. Document the ice, the damage and the dates for your insurer. Our roof leak insurance guide and roof warranty guide explain what each usually covers.
How does OYH Roofing handle ice dam repair?
OYH Roofing repairs, replaces and maintains flat roofs on commercial, industrial and institutional buildings across Ontario from its head office in Oakville. On an ice dam call we look at the building from inside and outside first, clear the drains, scuppers and gutters so water can leave the roof, repair the flashings, edge metal and membrane to the maker's details, check the insulation for water, and tell you in writing what caused the ice dam and what needs a designer, an electrician or an engineer.
See our completed projects, including the 53,000 sq ft industrial roof in Mississauga, the City of Mississauga building at 3185 Mavis Rd and the Marriott Hotel in Vaughan, and our pages on commercial roof leak repair in Toronto and in Mississauga.
Frequently asked questions
Can ice dams form on flat roofs?
Yes. RAYCHEM's heat cable manual notes that ice dams may occur on flat roofs at the edge flashing and at drains, and on commercial buildings they also form at gutters, scuppers, canopies and mansards. On a poorly drained flat roof, NRC notes, the ice can be hard to see, because meltwater freezes in a sheet instead of a ridge.
When to worry about ice dams on roof?
When ice builds at gutters, scuppers, edge metal or downspouts, when water appears inside along exterior walls or top-floor ceilings during a thaw, or when ice hangs over a door, walkway or parking area. Keep people clear of the area below, stay off the roof and call a roofer. Twisting, bending or cracking in the structure needs an engineer.
What is the best tool for removing ice dams?
On a membrane roof, makers accept plastic or rubber-edged shovels and soft brooms for snow, and CRCA names steam for clearing ice from drains. Metal shovels, picks, snow blowers and high-pressure water can cut or tear the membrane. No roofing maker we checked publishes a steam pressure or temperature limit, so ask yours before the work starts.
Can I remove ice dams myself?
Not on a commercial roof. CRCA tells owners to stay off the roof and use only qualified, insured roofing contractors, and Ontario's Ministry of Labour says workers on a roof must use fall-arrest or travel-restraint equipment. Snow can hide skylights and roof edges. From the ground, keep people away from falling ice and photograph the damage.
Is ice damming covered by insurance in Ontario?
It depends on your policy. The Insurance Bureau of Canada explains that insurance covers unexpected and accidental events, not damage from a lack of maintenance or wear over time. Water that an ice dam suddenly pushes inside may be covered; repeated ice damming from a known problem may not be. IKO's roof warranty, for example, excludes interior damage.
What can I put on my roof to stop ice dams?
No product stops them on its own. Heat cable can keep a path open for meltwater at edges, gutters and drains, but NRCA (U.S.) advises against it and points to heat and air leaks as the cause. CRCA warns that de-icing salts corrode metal flashings. The lasting fix is sealing air leaks, adding insulation at the roof edge and keeping drains clear.
Need ice dam damage repaired?
Tell us about your building and what you are seeing, and we will set up a roof assessment and a written quote.
Call 1-833-775-7663Request an assessment
Karol Rajkowski
Vice President · OYH Roofing
Karol Rajkowski is Vice President of OYH Roofing, an Oakville-based ICI flat-roofing contractor whose projects include the City of Mississauga building at 3185 Mavis Rd and the Marriott Hotel in Vaughan. Learn more about the OYH team.
Sources
- National Research Council Canada: Canadian Building Digest 89, Ice on Roofs (1967); CBD 193, Estimating Snow Loads on Roofs (1978); CBD 228, Sliding Snow on Sloping Roofs (1983). CMHC: About Your House CE13, Attic Venting, Attic Moisture, and Ice Dams (2007, archived). Natural Resources Canada: Keeping the Heat In, Section 5 (2024).
- Environment and Climate Change Canada, Canadian Climate Normals 1991 to 2020: Toronto Pearson, Toronto (City) and Hamilton A.
- CRCA: Advisory Bulletin, Ice on Roofs (January 1998); Canadian Roofing Reference Manual, 13.2, repair roofing problems (2020).
- IKO: snow removal from commercial roofs (2020, updated 2024); Commercial Technical Specification Manual, Part 15 (VER1225); Diamond Shield warranty sample (2021). SOPREMA: Form 100 warranty sample with the Form 901 Care and Maintenance Guide (2025, U.S.). Elevate: Owner's Manual (2023, U.S.; distributor copy). Carlisle: approved ice and snow melts for EPDM (U.S.).
- nVent RAYCHEM: IceStop roof and gutter de-icing installation manual, H58067 (2019). Electrical Safety Authority: property owner and manager obligations.
- NRCA, Professional Roofing (U.S.): Technical Elements (January 2008); Ice dam busting (June 2012); Surveying roof moisture (December 2025). J. Straube, Building Science Digest 135, Ice Dams (2006). IIBEC Interface: Roodvoets et al. (August 2010, U.S.).
- 2024 Building Code Compendium, January 16, 2025 edition: Volume 1 (Div. A 1.3.3; Div. B 4.1.6.2, 4.1.6.11, 5.3.1.2, 5.4.1.1, 5.6.2.2, 9.19.1, 9.26.5.1) and Volume 2 (Note A-5.6.1.2.(1)). Ontario: Occupiers' Liability Act, s. 3; Municipal Act, 2001, s. 122; O. Reg. 213/91, ss. 26 and 65; Reg. 851, s. 85.
- Ontario Ministry of Labour: Alert: snow loading and roof failures (updated September 15, 2026); Workers falling through skylights (updated April 5, 2022). IHSA: fall hazards around skylights. Insurance Bureau of Canada: Does my insurance cover damage caused by extreme cold?
- Municipal by-laws: City of Toronto Municipal Code Chapter 719 and Chapter 629; City of Mississauga Property Standards By-law 0654-1998; City of Brampton By-law 242-76; City of Markham By-law 2017-27; Town of Oakville By-law 2023-074.
- OYH Roofing project records: 53,000 sq ft industrial roof, Mississauga; City of Mississauga, 3185 Mavis Rd; Marriott Hotel, Vaughan (October 2026).
OYH Roofing, 2120 Speers Rd, Oakville, ON L6L 2X8 · 1-833-775-7663 · info@oyhroofing.ca