Charlottetown’s design snow load starts at 2.7 kPa on the ground, with a rain load stacked on top before that figure ever reaches a truss table. Run through the building code’s own formula, that combined number is what shows up on a permit application or a set of truss drawings for a roof on the Island. If you’re planning a re-roof or a new build anywhere in Prince Edward Island, take those figures straight to your municipal building department rather than assuming what your own roof needs to carry.
What is the ground snow load in Prince Edward Island?
The National Building Code of Canada 2020, in Appendix C’s Table C-2, lists Charlottetown at a ground snow load, Ss, of 2.7 kPa, with an associated rain load, Sr, of 0.6 kPa added on top. Both numbers matter for the same reason: a snowpack sitting on a roof through a thaw can soak up rain before it drains away or refreezes, and the Atlantic provinces get enough of that pattern that NBC 2020 bakes it into the design equation rather than treating snow and rain as separate problems.
From ground load to roof load
Ground snow load is not roof snow load, and mixing the two up is the single most common mistake a homeowner makes reading a truss drawing. The code’s actual formula is S = Is[Ss(Cb·Cw·Cs·Ca) + Sr]: a basic factor, Cb, scales the ground figure down for an ordinary roof, and then wind exposure, slope and snow-accumulation factors, Cw, Cs and Ca, push the result up or down again depending on the building’s shape and site. The number that ends up on a truss drawing is therefore always a calculated value, never the 2.7 kPa ground figure copied straight across.
This is the figure a building official checks against a permit application, and the one a truss manufacturer’s engineer plugs into span calculations before cutting lumber for a house near Charlottetown or anywhere else on the Island. Table C-2 lists Charlottetown specifically, because a single number for the whole province would hide real differences between a sheltered inland lot and an exposed shoreline site. If your address isn’t Charlottetown, ask your municipal building department which reference figures and site factors apply where you live.
Snow and wind design work on completely different bases from one country to the next. South of the border, a state like Kansas figures its roof loads in pounds per square foot under an entirely different code, as covered in Kansas’s roof snow load and wind rules. The Canadian kPa figures used here and any American psf figure are not interchangeable, and there is no honest conversion between the two.
How much snow can a roof hold in Prince Edward Island?
There’s no single depth of snow a roof in Prince Edward Island “can take,” and anyone quoting a number in inches is guessing. What a roof actually carries depends on its slope, its exposure to wind, and above all on where snow is allowed to drift, because drift load, not the flat design figure, is what actually breaks roofs.
Starting from Charlottetown’s 2.7 kPa ground snow load and 0.6 kPa rain load (NBC 2020, Table C-2), an ordinary heated, moderately sloped roof typically ends up carrying something on the order of seven-tenths of the ground value once the code’s basic factor is applied. A steep roof shedding snow readily can see that figure fall further. But the same formula pushes the number the other way wherever snow has somewhere to pile up: against a taller wall, below a dormer, in a roof valley, or on a lower roof next to a taller section of the same house. Those local drift zones can carry several times the flat-roof figure, and they are where structural failures actually happen.
Why depth alone tells you nothing
A foot of freshly fallen, dry snow weighs only a fraction of what a foot of wet, settled, late-winter snow weighs, and a layer that has partly melted and refrozen into ice weighs more again. That is why a foot of January powder and a foot of March slush are two completely different loads on the same roof, even though a tape measure reads the same number for both. It is also why raking snow off a roof after a light early storm buys little safety margin against a heavy, wet late-season one.
Watch for the signs that a roof is being asked to hold more than it should:
- Interior doors that suddenly stick or won’t latch
- New cracks in ceiling drywall or at wall-ceiling joints
- A ridge line that looks noticeably swayed from the ground
- Creaking or popping sounds from the attic 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 up, not to climb onto a loaded roof. A roof already showing distress is not a place to add your own body weight, and a structural concern belongs to a licensed engineer or your municipal building department, not a guess.
What wind speed must a roof withstand in Prince Edward Island?
Charlottetown’s reference hourly wind pressure, the figure NBC 2020 uses for structural design, is 0.56 kPa for a 1-in-50-year return period (NBC 2020, Appendix C, Table C-2). That’s a pressure, not a gust speed, and it’s built on a completely different measurement basis than an American mph figure on a weather forecast or hurricane advisory. Comparing the two directly doesn’t work: the Canadian code specifies a pressure load, full stop, and there is no honest way to turn it into a wind speed for comparison with a US figure.
The same table also carries a lower, 1-in-10-year pressure of 0.44 kPa for Charlottetown. That second figure is for serviceability, things like how much a wall assembly deflects or how much cladding flexes in ordinary storms, and it is never the number used for strength design. The 0.56 kPa, 50-year figure is what governs how a roof structure itself is built to resist failure.
What the pressure number actually governs
On a real roof, that pressure translates into a shingle’s wind rating, the nailing pattern the shingles are installed with, how the roof sheathing is fastened to the trusses, and the uplift connections tying the roof structure down to the walls below. Wind load doesn’t spread evenly across a roof. It concentrates at edges, rakes and ridges, where airflow separates and pulls hardest, which is why those areas lose shingles first in a storm and need the tightest fastening.
High wind pressure driven by an exposed, coastal, Atlantic location is arguably the more consequential figure here for anyone re-roofing, more than the headline snow number. It shows up in a shingle package’s wind rating, in how closely a roofer spaces nails, and in whether the structure has documented uplift connections at all, rather than just gravity and friction holding trusses to top plates. Neighboring New Brunswick sits in the same weather system and faces its own high design pressures, covered in New Brunswick’s roof snow load and wind rules, and the same logic about edges and fastening applies there.
As with the snow figures, 0.56 kPa is Charlottetown’s number specifically. A more exposed shoreline site elsewhere on the Island can see different local wind effects, and your municipal building department is the place to confirm what applies at your address.
Does Prince Edward Island require an ice barrier under the shingles?
An ice barrier is a self-adhering waterproof membrane installed directly on the roof deck, run up from the edge of the eave to a point past the interior line of the exterior wall. Its job isn’t to stop snow from sitting on the roof. It’s to stop meltwater that backs up behind an ice dam from finding a way through the shingles and into the deck below.
What actually causes an ice dam
Ice dams form when heat leaking out of a warm attic melts the underside of the snowpack higher up the roof slope, where the deck is still warm from the house below. That meltwater runs down under the snow until it reaches the eave overhang, which sits beyond the heated wall line and stays at outdoor temperature, and there it refreezes into a ridge of ice. Water backs up behind that ridge and, without protection, works its way under the shingles. Charlottetown’s coldest-month average low, -12.1°C (ECCC 1981-2010 climate normals), stays well below freezing for weeks at a stretch, and Charlottetown’s design snow load of 2.7 kPa ground snow plus 0.6 kPa rain load means there is routinely a substantial snowpack sitting on roofs while that cold holds. Together, those two figures describe exactly the conditions ice dams need: plenty of snow, and a long enough cold stretch to keep refreezing meltwater at the eave.
An ice barrier membrane protects the roof deck from the water an ice dam produces. It does not stop the dam from forming. Only air sealing the attic floor and bringing insulation up to a level suited to the local climate keeps the attic itself cold enough that the snowpack doesn’t melt from underneath in the first place. Charlottetown’s station falls in Natural Resources Canada’s climate zone 6, based on roughly 4,598 annual heating degree-days recorded there, itself a sign of how much heat a poorly sealed attic has available to leak upward all winter.
What the province’s code says
Prince Edward Island’s own construction rules are the Building Codes Regulations (EC177/20, as amended by EC179/24) under the Building Codes Act, derived from the 2020 edition of the National Building Code of Canada. The Minister of Housing, Land and Communities administers the code with the Building Standards Council, and municipalities carry out enforcement under agreement, a structure in force since March 31, 2024. That regulation sets the construction requirements builders and inspectors work from across the Island, and it’s the document your municipal building department applies when it reviews eaves protection and every other construction detail on a permit application. For the specific wording that applies to your roof, that department is the source to check, not a general guide like this one.
What roofing material suits Prince Edward Island best?
The right material here has to answer to three things at once: Charlottetown’s 2.7 kPa ground snow load plus 0.6 kPa rain load, its 0.56 kPa design wind pressure, and a climate cold enough to sit in Natural Resources Canada’s zone 6. None of the common roofing materials fails outright under those numbers, but each carries a different tradeoff.
| Material | Snow behavior | Wind consideration |
|---|---|---|
| Architectural asphalt shingles | Holds snow on the roof rather than shedding it suddenly | Wind rating and nailing pattern both need to match local pressure |
| Standing-seam metal | Sheds snow and ice in sudden slides once the surface warms | Panel clips and fastening carry the uplift load at seams |
| Slate or concrete tile | Its own weight adds directly to the snow load the structure already carries | Heavier assembly changes the uplift and dead-load math together |
Standing-seam metal’s snow-shedding advantage is also its main design problem: a roof that sheds well drops several feet of dense, wet snow all at once, and where it lands, over a doorway, a walkway or a parked car, is a decision that belongs on the design drawings, not something to discover after the first thaw. Slate and concrete tile carry real aesthetic and durability advantages, but their own dead weight stacks on top of the snow load figures above rather than replacing any of it, so a structure has to be sized for tile and snow together, not just for snow.
Fastening matters as much as the material
Where wind pressure governs, as it does at Charlottetown’s 0.56 kPa design figure, how a roof covering is fastened matters more than which covering is chosen. A shingle rated for high wind speeds that gets nailed with a standard nailing pattern performs like a standard shingle, not like the product on the wrapper. The same is true of the underlayment beneath it: a self-adhering underlayment at the eaves and a synthetic underlayment across the field of the roof both need to be installed to the manufacturer’s own wind-exposure instructions, not just laid down and covered over. Getting the deck, underlayment and fastening details right is a step this page assumes is already understood; the fundamentals are covered in our general guide to Roofing.