St. John’s roofs are engineered for snow sitting on top of rain, not for snow alone. That combination is the whole reason a roof here is built differently than a roof somewhere with less coastal weather to contend with. If you’re pulling a permit or ordering trusses, get the current design figures and the code edition in force from your municipal building department, because Newfoundland and Labrador has no single set of numbers that applies province-wide.
What is the ground snow load in Newfoundland and Labrador?
The ground snow load used for St. John’s, Newfoundland and Labrador is Ss = 2.9 kPa, with an additional rain-on-snow load of Sr = 0.7 kPa, published in the National Building Code of Canada 2020 (NBC 2020), Appendix C, Table C-2, for the St. John’s reference station at 65 metres elevation. Both numbers matter. The rain figure is added because Canadian code writers assume rain can fall onto standing snow and soak into it before it drains off, and along this coast that assumption carries real weight.
Ground load is not roof load
Neither number is what a rafter actually carries. The ground snow load is not the roof snow load: the code converts Ss into a specified roof value through the formula S = Is[Ss(Cb·Cw·Cs·Ca) + Sr], where the basic factor Cb typically brings an ordinary sloped roof down to a fraction of the ground figure, and the slope factor Cs and accumulation factor Ca then push that number up or down again depending on roof shape, exposure and where snow is free to slide or pile up. Sr is added on afterward, largely unchanged.
This is the figure that shows up on truss drawings and structural plan review, not something a homeowner calculates by eye. A designer working from the St. John’s table has to run the whole formula, not just quote Ss, before a permit gets issued. Elsewhere in the province, particularly at higher elevations and across Labrador, Table C-2 lists different ground values entirely, so a figure taken from St. John’s has no business on a plan for another municipality. If you need the number for a specific address, ask the local building department which table entry and which code edition apply there.
How much snow can a roof hold in Newfoundland and Labrador?
There is no single depth of snow a roof in this province can safely hold, because the answer depends on the roof’s slope, its exposure, and what the snow itself has turned into. For an ordinary heated sloped roof, the code’s basic factor typically lands the specified roof load near 0.7 of the ground figure derived from St. John’s Ss and Sr. A steep roof can run lower again. A shallow roof, or one that catches drift, runs higher.
Drift is where roofs actually fail
Drift is the part of this equation that catches people out. Snow does not sit evenly across a roof plane. It piles against parapets, behind chimneys, below dormers, and especially where a lower roof sits next to a taller wall or a taller section of the same house. In those spots the accumulated depth, and the load, can run well past the open-field figure the ground snow load describes. The same drift mechanics show up in mountain snow country generally, including in the roof snow load and wind speed rules for Wyoming, where high-elevation drift against long roof valleys is a routine design problem rather than an edge case.
Depth alone doesn’t tell you the load, because snow density changes as it ages. Fresh, light snow runs roughly 0.25 to 0.35 kPa for every 30 centimetres of depth. Once that snow settles, gets rained on, or turns to slush, the same depth can weigh two to three times as much. An ice layer buried in the pack adds still more. That’s why a foot of snow that fell in a cold January flurry is not the same load as a foot of wet March snow sitting on a warm roof.
Watch for signs a roof is carrying more than it should:
- Interior doors that suddenly stop closing properly
- New cracks appearing in ceiling drywall, especially near the ridge
- A visibly sagging ridge line or roof plane
- Popping or cracking sounds from the attic under load
If you see any of that, raking snow off from the ground with a roof rake is the safe response. Climbing onto a loaded roof to shovel it is not, and it’s exactly the wrong moment to add your own weight to a structure that may already be stressed. For anything beyond raking reachable eave snow, call your municipal building department or a licensed engineer rather than guessing.
What wind speed must a roof withstand in Newfoundland and Labrador?
The design wind pressure for St. John’s, Newfoundland and Labrador is q = 0.78 kPa, the 1-in-50-year hourly wind pressure from NBC 2020, Appendix C, Table C-2, and it’s this figure that NBC Part 4 and Part 9 use for structural design, not a forecast wind speed and not a gust reading off a weather app. The same table also carries a 1-in-10-year value of 0.61 kPa, which is used for serviceability checks like cladding deflection and comfort, never for the strength calculations that decide fastening and framing.
What the pressure actually governs
These are pressures, not speeds, and the Canadian code defines them on a different basis than an American gust-speed rating. There’s no honest way to convert one to the other or to line them up against a hurricane bulletin’s headline number. Readers used to American coastal wind ratings, including the figures used on the roof snow load and wind speed page for Washington, will notice the two systems simply don’t translate, and that’s expected rather than an error on either page.
What matters practically is that St. John’s carries a notably high wind pressure for a Canadian city, and that pressure drives real decisions on a roof: the wind rating stamped on a shingle bundle, the nailing pattern used to fasten sheathing to the trusses, and the metal connectors that tie the roof structure down to the walls so uplift can’t lift it off in a gust. Edges, rakes and ridges fail first in high wind, because that’s where uplift concentrates, which is why inspectors pay closer attention to fastening at those lines than in the middle of a roof plane. Confirm the design pressure and the fastening schedule your permit requires with your municipal building department before a re-roof or new build goes ahead.
Does Newfoundland and Labrador require an ice barrier under the shingles?
An ice barrier is a self-adhering waterproof membrane run along the eaves, up past the point where the interior wall line meets the roof, so that water backing up behind an ice dam has no seam to get through before it reaches the roof deck. It doesn’t stop snow from accumulating and it isn’t there to reduce load. It’s there for meltwater.
What actually causes an ice dam
Ice dams form because heat escaping into the attic melts the underside of the snowpack, that meltwater runs down the roof slope, and it refreezes the moment it reaches the colder eave beyond the heated part of the house. St. John’s mean minimum temperature in the coldest month is -8.7 °C (-8.7 °C), per Environment and Climate Change Canada’s 1981-2010 climate normals, cold enough that this freeze-thaw cycle at the eave is a routine winter event rather than a rare one, and it’s happening on top of a roof already carrying the province’s substantial snow and rain-on-snow load. Natural Resources Canada places St. John’s in climate zone 6 based on roughly 4,755 annual heating degree-days, which is the same measure that decides how much insulation a house needs to keep that attic cold enough to prevent melting in the first place.
The membrane protects the deck from water damage after the fact. It does nothing to stop the dam from forming. Sealing air leaks into the attic and adding enough attic insulation are the only measures that address the actual cause, and a homeowner who buys the membrane without addressing attic heat loss has bought protection against the symptom, not the problem.
No single provincial rule
There is no provincial building code governing houses in Newfoundland and Labrador. The National Building Code is adopted municipality by municipality, and the province’s fire-safety regulation that adopts it expressly excludes one- and two-unit dwellings from that adoption. That means there is no single ice barrier answer for the province, because it depends on which code edition a given municipality has adopted:
- St. John’s has its own statute governing which code edition applies
- Mount Pearl has its own statute, separate from St. John’s
- Corner Brook has its own statute as well
The only reliable way to find out whether ice barrier membrane is required, and how far up the roof slope it must run, is to ask the building department in the specific municipality where the house sits, since the answer changes from one town to the next in this province in a way it doesn’t in most others.
What roofing material suits Newfoundland and Labrador best?
The right category of roofing material here follows from three things already covered above: a substantial ground snow load with a large rain-on-snow component at St. John’s, a high design wind pressure at the same location, and a cold climate zone that keeps attics working hard against ice dams all winter. None of that changes which product is “best” in the abstract, but it does change what each material category is best at.
| Material | Wind performance | Effect on roof load |
|---|---|---|
| Architectural asphalt shingles | Wind rating printed on the bundle, only as good as the fastening pattern used underneath | Adds little dead weight to the snow load already carried |
| Standing-seam metal | Performs well against uplift when properly clipped and fastened | Sheds snow readily, which means the snow has to land somewhere safe, not on a doorway, walkway or driveway below |
| Slate or concrete tile | Heavy enough that wind uplift is rarely the limiting factor | Its own dead weight is added on top of the design snow load, which the structure must be sized to carry |
Whatever category goes on the roof, the fastening and the underlayment matter more than the material once wind pressure is doing the governing. A shingle rated for high wind that’s nailed to a lower standard performs to that lower standard, not to the number on the wrapper. That’s as true of a small re-roof as it is of new construction, and it’s a large part of what a building inspector is actually checking when they climb the ladder. Anyone doing roofing work in this province, on new construction or a replacement, is working against the same St. John’s-derived figures covered above, and municipalities elsewhere in the province, especially those at higher elevation or further into Labrador, are assigned different ground snow and wind figures in the same NBC table, so the material decision should follow the local numbers rather than the ones quoted here.