Montréal’s building code numbers for a new roof start with a ground snow load of 2.6 kPa and a wind pressure of 0.44 kPa, the two figures that drive every truss and fastening calculation in the region. Neither number is what actually lands on your rafters: the code applies exposure, slope and thermal factors before a ground figure becomes a roof load. If you’re pulling a permit or reviewing truss drawings for a house near Montréal, ask your municipal building department which factors were applied and whether your site matches the reference conditions used for that 2.6 kPa figure.
What is the ground snow load in Quebec?
The ground snow load used for design near Montréal is Ss = 2.6 kPa, with an additional Sr = 0.4 kPa of associated rain load, both published in the National Building Code of Canada 2020, Appendix C, Table C-2, under the entry for Montréal (City Hall), elevation 20 m. That pairing matters: Canadian code assumes rain can fall onto standing snow, so the rain component gets added on top of the snow figure rather than replacing it in years when a thaw arrives before the snow does.
This is a ground figure, not a roof figure, and the distinction is the single most common mix-up on this subject. The code doesn’t hand a truss designer 2.6 kPa and tell them to frame for it. Instead it runs the ground and rain values through a formula, S = Is[Ss(Cb·Cw·Cs·Ca) + Sr], where a basic factor lowers the number for an ordinary roof, and separate factors adjust for wind exposure, roof slope and snow accumulation before the load ever reaches a rafter. The specified roof load that ends up on a truss drawing is a derived number, never the 2.6 kPa printed in Table C-2.
Where the figure gets used
A structural engineer or truss manufacturer pulls this ground figure at the start of a design, then works through the formula for the specific roof: its slope, whether it sits in a sheltered or exposed spot, and whether the space below is heated. That derived load is what shows up on the stamped truss drawings a builder submits with a permit application, and it’s what a plan reviewer checks against. If you’re comparing quotes or reviewing drawings, the number to look for is the one already run through the formula, not the raw ground figure.
The code an inspector actually enforces in this province is the Code de construction du Québec, Chapter I – Building, built on the NBC 2020 and administered by the Régie du bâtiment du Québec for the buildings it covers. For a house of two storeys or fewer, though, Chapter I doesn’t apply at all: the municipal building by-law decides which edition of the National Building Code governs, so the exact factors a truss designer applies can differ from one municipality to the next even when everyone starts from the same Montréal-area climate data. Elevation and local exposure push the usable ground figure up in higher terrain and down along the river valley, so a figure measured at Montréal’s City Hall station is a starting point, not a province-wide constant.
How much snow can a roof hold in Quebec?
There’s no single depth or weight a Quebec roof “can take,” because the answer depends on the roof’s slope, its exposure, and what the snow itself has turned into by the time it matters. What the code gives instead is a derived design load, not a household rule of thumb.
From ground load to roof load
Applying the code’s usual basic factor to the NBC 2020 ground figure for Montréal, 2.6 kPa, an ordinary sloped, heated house roof lands somewhere near 1.8 kPa before slope and drift factors move it further. That’s an illustrative approximation of the general reduction the formula applies, not a figure a truss designer would use directly, since the exact basic, wind, slope and accumulation factors depend on that specific roof’s geometry and exposure. A steep roof shedding snow readily can end up carrying less than that. A roof with a wall or a taller neighboring roof feeding drift onto it can end up carrying a great deal more.
Drift is where roofs actually fail, far more often than uniform accumulation does. Snow blown off a taller roof section piles against a lower one, wind pushes drift up against a parapet or a dormer, and a valley between two roof planes collects snow that never reaches the eave to melt or slide off. Those local pockets can carry several times the uniform design load calculated for the rest of the roof, which is why an accumulation factor exists in the code’s formula in the first place.
Why depth alone tells you nothing
A foot of fresh, dry January snow and a foot of wet March snow are not the same load. Fresh light snow runs roughly 5 to 7 pounds per square foot for every foot of depth. Once it settles, gets rained on, or partly melts and refreezes, that same foot of depth can weigh two to three times as much, and a layer of ice on top adds more still. A roof that comfortably carried an early season snowfall can be under real stress carrying the same depth of late-winter, waterlogged snow, especially if new snow lands on top before the old layer has a chance to settle or slide off.
Watch for signs that a roof is being asked to carry more than it should:
- Interior doors that suddenly stick or stop closing properly
- New cracks in ceiling drywall, especially running along a ridge line
- A visibly sagging ridge or roof plane when viewed from the ground
- Creaking or popping sounds from the attic or roof structure under load
If you see any of that, the safe response is to rake snow from the ground with a roof rake, working from the eaves, and to call your municipal building department or a structural engineer for anything beyond what a rake can reach. Climbing onto a snow-loaded roof is not the way to check it: it adds your own weight to a structure that may already be near its limit, on a surface that’s slick and pitched.
What wind speed must a roof withstand in Quebec?
The design figure for Montréal is a reference hourly wind pressure of q = 0.44 kPa, for a 1-in-50-year return period, published in NBC 2020, Appendix C, Table C-2, under the Montréal (City Hall) entry. That’s the value NBC Part 4 and Part 9 use for structural design, meaning it’s the number that governs how a roof’s framing and connections are engineered to resist wind, not a forecast wind speed and not a gust reading off a weather report.
It’s worth being precise about what kind of number this is. The Canadian code expresses wind action as a pressure in kilopascals, derived from its own statistical and aerodynamic basis, not as a mile-per-hour gust the way some other codes do. The two systems aren’t interchangeable, and converting one into the other, or setting them side by side, produces a number that looks precise but means nothing, because the underlying formulas differ. If you want a sense of how differently another region frames the same problem, Oregon’s snow and wind load rules are built on a completely different code basis, which is exactly why the figures from the two places can’t be compared directly.
Table C-2 also carries a lower figure, 0.34 kPa, for a 1-in-10-year return period. That’s a serviceability value, used to check things like cladding deflection and comfort under wind, not the number an engineer designs the structure’s strength against. The 0.44 kPa figure is the one that governs strength.
What the pressure actually governs
On a house roof, this wind pressure shapes several practical decisions: the wind rating a shingle product needs to carry, the nailing pattern used to fasten it, how the roof sheathing itself is fastened to the framing, and the uplift connections tying the roof structure down to the walls below. Edges, rakes and ridges are where uplift concentrates, which is why building inspectors pay closer attention to fastening patterns in those zones than across the open field of a roof.
As with the snow load, this figure belongs to the Montréal reference station specifically. Other parts of the province, particularly higher, more exposed sites and stretches of the St. Lawrence with less shelter, can see different wind conditions, and the reference figure a truss or fastening design actually uses depends on the site your municipality’s building by-law calls for. Check with your municipal building department for the value that applies at your address before assuming Montréal’s figure carries over.
Does Quebec require an ice barrier under the shingles?
An ice barrier is a self-adhering waterproof membrane installed on the roof deck, running from the edge of the eave up past the point where the exterior wall sits below, sometimes further up a valley or around a dormer. It isn’t there to stop snow from accumulating. It’s there to stop meltwater from an ice dam finding its way under the shingles and into the deck once the dam has already formed.
What actually causes an ice dam
Ice dams form because heat escaping from the living space into the attic warms the underside of the roof deck unevenly. Snow near the ridge, over the warmer part of the attic, melts first. That meltwater runs down the roof slope until it reaches the cold overhang beyond the heated wall line, where it refreezes, building up a ridge of ice that backs water up behind it. The membrane protects the deck from that backed-up water. It does nothing to stop the dam from forming in the first place, because the dam is caused by heat loss and attic insulation, not by the membrane’s absence.
Montréal’s coldest month has a mean daily minimum temperature of about -14.1°C, according to Environment and Climate Change Canada’s 1981-2010 climate normals. Combined with the ground snow load already covered above, that’s a cold, snowy combination where heat loss into a poorly insulated attic has both the temperature difference and the snow cover to build a dam over a sustained stretch of winter. That’s the condition an ice barrier is meant to defend against here, not an occasional light frost.
What the code says, and who enforces it
The code in force in this province is the Code de construction du Québec, Chapter I – Building, based on the NBC 2020 and administered by the Régie du bâtiment du Québec for the buildings it covers. It has been in force since April 17, 2025, with a transition period running to October 17, 2026. But most houses, meaning dwellings of two storeys or fewer with eight units or fewer, are exempt from Chapter I entirely. For those houses, it’s the municipal building by-law that decides which edition of the National Building Code applies, including whatever eave protection provisions that edition carries. That means the exact extent of ice barrier coverage required on a given re-roof can differ from one municipality to the next, even for houses a few kilometres apart.
Given that, the honest answer for a specific house is to ask the municipal building department which NBC edition their by-law has adopted and what it requires at the eaves, rather than assuming a single provincial rule covers every roof. Fixing the attic’s air sealing and insulation levels, not just adding the membrane, is the only way to address the cause rather than the symptom, and that combination of cold and snow isn’t unique to Quebec: Kentucky’s snow load and ice barrier rules are built around a much milder, shorter cold season, which is part of why its eave protection requirements read so differently.
What roofing material suits Quebec best?
The mix of a heavy ground snow load, a substantial wind pressure and a cold heating profile near Montréal, in Natural Resources Canada’s climate zone 6, means the honest answer is about trade-offs, not a single best material. Each option changes how snow behaves on the roof and how much load the structure itself has to carry before any snow even lands on it.
Comparing the main options
| Material | How it handles snow | What it adds to the structure | Wind consideration |
|---|---|---|---|
| Architectural asphalt shingles | Holds snow in place rather than shedding it quickly | Relatively light dead load on its own | Wind rating and nailing pattern must match the shingle’s published rating |
| Standing-seam metal | Sheds snow and ice in sudden slides once the sun warms the panel | Light, but the slide itself is a hazard needing a planned landing zone | Panel clips and seams need fastening specified for the site’s wind pressure |
| Slate or concrete tile | Sheds slowly, similar to shingles | Substantial dead weight added on top of the snow load the structure must carry | Requires a structure engineered for the combined dead load and wind uplift |
Standing-seam metal’s snow-shedding behavior is often sold as an advantage, and it can be, but a roof that sheds snow well has to put that snow somewhere. A slide off a metal roof above a front door, a walkway or a driveway is a design decision, one where the lower roof edge, a snow guard, or the landscaping below needs to account for a sudden load of sliding snow and ice, not something to discover the first time it happens.
Slate and concrete tile carry their own dead weight in addition to whatever snow load the code requires the structure to resist, so a re-roof from asphalt shingles to tile on an existing structure is a structural question first, one for an engineer to check against the original design, not just a materials swap.
Fastening decides more than the material label
A shingle rated for high wind performs only as well as the pattern it’s nailed to. The wind pressure Montréal’s roofs are designed against drives fastening schedules, sheathing attachment and the underlayment beneath the visible material, and skipping any of those while using a premium shingle just moves the failure point from the shingle to the fastener. Choosing a roofing material for this climate means asking a contractor for the fastening schedule and underlayment spec that matches the local wind and snow figures, not just the brand name of the shingle, tile or panel on top.