Yellowknife’s building permits start from a ground snow load of 2.2 kPa, with another 0.1 kPa added for rain falling on top of that snow. Neither number is what a rafter actually carries: the code shrinks and reshapes that ground figure before it becomes a roof load. If you are pulling a permit or ordering trusses anywhere in the territory, ask your municipal building department for the site-specific roof load calculation rather than assuming a fixed share of the ground figure.
What is the ground snow load in Northwest Territories?
The ground snow load the National Building Code of Canada assigns to Yellowknife is Ss = 2.2 kPa, with an additional Sr = 0.1 kPa rain-on-snow load. Both numbers come from NBC 2020, Appendix C, Table C-2, the National Research Council’s table of climatic design data for named localities, listed for the Yellowknife reference station at 160 metres elevation.
That figure describes what piles up on open, flat, unobstructed ground around Yellowknife over a typical winter. It is not what a roof carries. The code runs that ground value through a formula, S = Is[Ss(Cb·Cw·Cs·Ca) + Sr], before it becomes the specified roof snow load an engineer stamps on a set of drawings. Cb is a basic roof factor that usually reduces the ground number for an ordinary house roof. Cw accounts for wind exposure, Cs for roof slope, and Ca for the way snow piles up unevenly instead of lying flat. Is is an importance factor tied to the building’s use. Confusing the ground figure with the roof figure is the single most common mistake a homeowner or a first-time builder makes reading a truss drawing.
Who actually uses this number
A plan reviewer at a municipal building department checks the specified roof load against these factors before issuing a permit. A truss manufacturer designs the webbing and connector plates to that load, not to the ground figure. A roofing crew never sees the number directly, but the nailing schedule and deck thickness they’re handed were sized against it. Table C-2 lists dozens of Northwest Territories communities separately from Yellowknife, because a single territorial number would be meaningless: Inuvik, Hay River, Fort Smith and the rest of the territory each carry their own listed ground snow and rain values in the same table, and none of them should be assumed to match Yellowknife’s.
None of this tells an individual homeowner whether their own roof is adequate. That determination belongs to the plans reviewer or a licensed engineer working from the actual roof geometry, and to the municipal building department that issued the permit.
How much snow can a roof hold in Northwest Territories?
There’s no single number that answers this, because the load a roof actually carries depends on slope, exposure and where snow is allowed to pile up, not just on the Yellowknife ground figure. What the National Building Code gives is the method: take a fraction of the 2.2 kPa Yellowknife ground snow load (NBC 2020, Appendix C, Table C-2) for a simple, ordinary sloped roof with clear exposure, roughly seven-tenths of it once the basic roof factor is applied, add back the 0.1 kPa rain load, and you land somewhere near 1.6 kPa for a plain gable roof before wind exposure or slope push it up or down again. A steeper roof reduces that further. A shallow roof, or one tucked behind a taller wing of the same house, can push it well past the ground figure.
Drift is where roofs actually fail
Snow does not distribute itself evenly. Wind strips it off exposed slopes and dumps it against parapets, behind dormers, in valleys where two roof planes meet, and onto a lower roof sitting beside a taller one. The accumulation factor in the code exists specifically for these spots, and it can multiply the flat-roof load several times over in a drift zone a few feet wide. A roof engineered for the field load with no allowance for drift at these details is the kind of gap an inspector is trained to look for and a homeowner usually is not.
Snow weight also changes with what the snow has become. Fresh, dry powder is mostly trapped air, so a given depth of it weighs far less than the same depth once it has settled, gone wet, or glazed with ice. Settled or wet snow can weigh two to three times as much as fresh powder at the same depth, and a layer of ice sitting on top adds more again. A two-foot snowfall in November is not the same load as two feet of packed, half-melted March snow sitting on a frozen base underneath.
Watch for signs that a roof is carrying more than it should:
- Interior doors that suddenly stick or won’t latch
- New cracks in ceiling drywall, especially near load-bearing walls
- A ridge line that looks like it’s sagging when viewed from the street
If you see any of that, raking snow off from the ground with a roof rake is the safe response. Climbing onto a roof that may already be overloaded is not, and it’s exactly the situation where an already-stressed structure meets an added point load it was never designed for.
What wind speed must a roof withstand in Northwest Territories?
The Canadian code doesn’t publish a wind speed for Yellowknife at all. It publishes a pressure: q = 0.4 kPa, the reference hourly wind pressure for a 1-in-50-year return period, from NBC 2020, Appendix C, Table C-2. That’s the figure NBC Part 4 and Part 9 use for structural design, the number an engineer plugs into the load equations that produce a truss uplift connection or a sheathing fastening schedule. It is not a gust speed, and it isn’t comparable to the mph figures on a US weather report or a hurricane advisory. The two systems measure different things on different bases, so there’s no honest way to convert one into the other.
The same table also lists a lower 1-in-10-year pressure for Yellowknife, 0.31 kPa. That number is for serviceability, things like cladding deflection and comfort under everyday wind, and it has no place in a strength calculation. Only the 1-in-50-year figure governs structural design.
What the pressure actually governs
On a roof, this pressure drives the shingle wind rating a manufacturer’s product needs to carry, the nailing pattern that fastens each course, the sheathing fastening schedule that ties the deck to the trusses, and the uplift connectors, straps or clips, that tie the roof structure down to the walls. Failures under wind load concentrate at the edges: eaves, rakes and ridges see the highest suction as wind pulls up and over the roof plane, which is why those details get the tightest nailing and the strongest connectors on a wind-engineered roof.
Neighboring Nunavut carries its own set of ground snow and wind pressure figures, worked through in our Nunavut’s roof snow load and wind rules guide, and the two territories should never be assumed to share a number just because they’re both far north. As with the snow figure, none of this tells you whether a particular roof meets code. That determination sits with the municipal building department reviewing the permit, or with a licensed engineer.
Does Northwest Territories require an ice barrier under the shingles?
An ice barrier is a self-adhering waterproof membrane installed along the eaves, run up the roof slope far enough to pass the interior wall line below. It isn’t there to stop snow. It’s there to stop meltwater that backs up behind an ice dam from working its way under the shingles and into the roof deck.
What actually causes an ice dam
Heat escaping from the living space into the attic warms the underside of the roof deck. Snow sitting over that warm section melts, runs down the slope, and reaches the eave, which sits over the unheated overhang and stays cold. The water refreezes there, and the ice that builds up backs meltwater upstream of it right under the shingles. The membrane protects the deck from that backed-up water. It does nothing to stop the dam from forming in the first place. Only air sealing the attic floor and adding enough insulation to keep the whole roof deck uniformly cold will do that.
Yellowknife’s coldest month has a mean daily minimum of about -29.5°C, according to Environment and Climate Change Canada’s 1981-2010 climate normals for the Yellowknife reference station. Combined with a ground snow load of 2.2 kPa plus 0.1 kPa rain load (NBC 2020, Appendix C, Table C-2) sitting on roofs for months at a time, the conditions that produce ice dams, deep snow cover and long stretches of hard cold, are squarely in place here. The Yellowknife A weather station also logs roughly 8,147 heating degree days below 18°C a year, which places the area in Natural Resources Canada’s climate zone 8, the coldest of the agency’s insulation zones. That’s the real argument for prioritizing attic insulation and air sealing over the membrane alone.
The territory’s own code is the National Building Code of Canada as adopted by the Fire Prevention Regulations, amended with effect from October 1, 2024, and administered by Municipal and Community Affairs’ Office of the Fire Marshal. Municipalities such as Yellowknife issue permits under their own by-laws layered on top of that adopted code. The specific eave membrane extension required for a given roof, how far up-slope it must run, depends on roof pitch and on the by-law your municipality applies. Check with your municipal building department for the eave protection clause that applies to your roof before you re-roof, rather than assuming a fixed distance.
What roofing material suits Northwest Territories best?
Start from what’s already on this page: a Yellowknife ground snow load of 2.2 kPa plus 0.1 kPa rain (NBC 2020, Appendix C, Table C-2), a 1-in-50-year wind pressure of 0.4 kPa, and a climate zone 8 rating from Natural Resources Canada. That combination, heavy snow sitting for months and a real wind pressure to fasten against, shapes which category of roofing makes sense here more than any single material’s reputation does.
| Material | How it handles snow | What it adds to the load calculation |
|---|---|---|
| Architectural asphalt shingles | Holds snow in place on the roof rather than shedding it, relies on the deck being sized for the full accumulated load | Light itself, but needs a wind rating and nailing pattern matched to the local pressure |
| Standing-seam metal | Sheds snow in slides once the roof warms, sometimes suddenly and in large sheets | Light dead load, but the slide has to land somewhere that isn’t a doorway, walkway or parked vehicle |
| Slate or concrete tile | Holds snow similarly to shingles, doesn’t shed in slides | Adds substantial dead weight of its own on top of the snow load the structure already carries |
Fastening matters as much as the material
Where wind pressure governs the design, how a shingle or panel is fastened decides more than which product line it came from. A shingle rated for high wind performs to a lower standard the moment it’s nailed with an under-spec pattern or laid over an underlayment that isn’t sealed at the laps. The same logic applies to standing-seam metal: the clip spacing and seam type matter more than the panel’s own wind rating on paper.
If you choose a metal roof for its snow-shedding behavior, work out where the slide lands before you install it, not after the first slide takes out a railing or buries a walkway. The same slide-versus-hold trade-off shows up in heavy-snow US states, covered from a different code’s perspective in our Colorado’s roof snow load and wind rules guide. None of this settles which material is “best” in the abstract. It settles what each one is best at, and what it demands from the rest of the roof assembly to actually perform that way here.