FAQs on Snow and Wind Loads for Steel Buildings

If you order a steel building before the site snow and wind loads are set, you can end up with permit delays, design changes, and added cost. In Canada, roof snow and wind loads are based on the exact site, the building use, the roof shape, nearby terrain, and drift risk. Even two buildings with the same size can need very different framing.

Here’s the short version:

Snow load is not one number. It can include ground snow, rain-on-snow, roof slope, wind exposure, and drift at parapets, steps, and valleys.
Wind load is not just for the main frame. It also affects cladding, doors, girts, purlins, and connections.
Your permit set must match the exact site. A generic drawing package or the wrong postal code can trigger review comments.
Serviceability matters too. A code-compliant building can still have door issues or panel movement if deflection is not checked well.
Quotes only make sense when the design basis matches. A low quote based on lighter loads is not the same building.

A few numbers show how much site conditions can vary. Vancouver may use 0.5 kPa ground snow and 1.5 kPa rain load, while Quebec City may use 3.5 kPa ground snow. Wind values vary too, from about 0.36 kPa in Vancouver to 0.55 kPa in St. John’s.

Snow Load Capacity Is More Important Than You Think!!!

Quick Comparison

Canadian City Snow & Wind Loads Compared: NBCC Design Values

City	Ground snow (Ss)	Rain load (Sr)	Wind pressure (q)
Vancouver, BC	0.5 kPa	1.5 kPa	0.36 kPa
Toronto, ON	1.0 kPa	0.4 kPa	0.40 kPa
Ottawa, ON	2.1 kPa	0.5 kPa	0.40 kPa
Quebec City, QC	3.5 kPa	0.7 kPa	0.45 kPa
St. John’s, NL	2.8 kPa	1.0 kPa	0.55 kPa

My takeaway: before I compare steel garage kit prices, I’d want the supplier to confirm the exact site, the stated kPa values, the building importance category, and whether drift and unbalanced snow checks are included. That keeps the quote, permit package, and final design on the same page.

Canadian snow load standards for steel building roofs

Roof snow loads for steel buildings are set by Part 4 of the NBCC. Appendix C lists the ground snow load (Ss) and rain load (Sr) for each site in kilopascals (kPa), based on a 1-in-50-year return period. Those site values are then used to work out the roof design load.

The standard roof snow load formula is S = Is [Ss (Cb Cw Cs Ca) + Sr].

The Sr term matters because rain absorbed into the snowpack adds weight. In coastal areas like Vancouver, it can reach 1.5 kPa. Site-to-site differences can be huge too. For instance, Quebec City’s ground snow load (Ss) is 3.5 kPa, while Vancouver’s is 0.5 kPa. And because the NBCC is adopted with local amendments, mountain, lake-effect, and high-elevation sites may face stricter rules.

How roof snow load is calculated from site data

The factors below adjust the base load for site conditions:

Factor	Name	Purpose
Is	Importance Factor	Scales load by building use: 0.8 (low), 1.0 (normal), 1.15 (high), 1.25 (post-disaster)
Ss	Ground Snow Load	Baseline 1-in-50-year snow weight for your location (kPa)
Sr	Rain Load	Adds weight from rain absorbed into the snowpack
Cb	Basic Roof Factor	Standard factor for roof shape, typically 0.8
Cw	Wind Exposure Factor	Adjusts for snow blown off or onto the roof; reductions generally limited to rural areas
Cs	Slope Factor	Reduces load on steeper roofs that shed snow more readily
Ca	Accumulation Factor	Increases load where drifting is expected (parapets, steps, valleys)

Here’s the practical takeaway: a 12 m × 18 m (roughly 40 ft × 60 ft) steel building in Calgary and the same building in Ottawa can need very different structural designs, even when the building layout is identical.

Where drifted and unbalanced snow loads become a concern

Uniform snow loads are just the starting point. On many projects, drifts at multi-level roofs and parapets can control the design of some members.

Drift buildup is most common at roof steps, parapets, canopies, mechanical penthouses, and locations beside taller structures. The Ca factor accounts for these conditions, and it can push local loads far above the base roof value. In some cases, drift loads at roof steps or parapets can reach 2.7 times the uniform roof snow load.

Sheet metal roofs tend to shed snow, which means the load can shift to lower roof areas. If an upper sloped roof slides snow onto a lower roof, that lower structure must be designed for a triangular surcharge load with its peak at the upper wall.

Unbalanced loads on gable roofs also matter. Wind can move snow to one side of the roof, which may create lateral thrust or torsional effects that a simple uniform-load check will miss. These cases should be shown in the engineered drawings.

Snow is only one side of the design check; wind loads can be just as controlling.

Wind load standards for low-rise steel buildings

Wind design for low-rise steel buildings in Canada follows NBCC Part 4: p = I_W · q · C_e · C_t · C_g · C_p, with q taken from the 50-year return-period wind data and I_W based on building importance. That pressure doesn’t apply only to the main frame. It also needs to be checked for the cladding, doors, connections, girts, and purlins.

That matters because wind design goes well past the primary structure. Secondary components can face higher local pressures than the frame itself. Under NBCC practice, the gust effect factor (C_g) is usually 2.0 for the main structural system and 2.5 for cladding and secondary members.

Wind and snow also aren’t piled together at full value. NBCC load combinations use a principal-and-companion approach, so when one climate load controls, the other is reduced. In practice, that can mean snow combined with wind at 0.4×, or wind combined with snow at 0.5×, depending on the governing case.

How terrain exposure, building openings, and roof shape affect wind pressure

The exposure factor (C_e) reflects both building height and the terrain around it. A building in open terrain sees more wind pressure than the same building in a sheltered area. For example, a 10 m high building in open terrain has a C_e of 1.0, while that same 10 m building in urban terrain drops to 0.70.

Pressure coefficients (C_p) deal with wall and roof shape, and internal pressure has to be checked too when a building has large openings. That’s a big issue for warehouses and agricultural buildings with large overhead doors. If one of those doors is open, the building can fall into the highest internal-pressure case.

Internal pressure can drive uplift just as hard as the wind on the outside.

Buildings on hills or escarpments need a topographic factor (C_t) to account for wind speed-up effects. On some sites, that factor can push wind loads 50% to 100% above what you’d assume on a flat site.

What owners should know about building performance under wind

Code compliance covers both strength and serviceability. That second part often gets less attention, but it’s where many day-to-day problems show up. Too much movement can make overhead doors bind, push cladding panels past their deflection limits, or leave occupants uneasy during high winds.

In windy areas, engineers look closely at sway and cladding deflection during design review. Good serviceability design helps avoid panel damage and door alignment problems. Those limits should appear on the engineered drawings submitted for permit review.

Permits, engineered drawings, and site-specific compliance

Snow and wind calculations need to show up in the permit package for the exact site. That point matters more than many buyers expect. Even if the building design is solid, the permit set still has to be built around the job site itself. The engineering package has to match the exact location, not a rough stand-in or a generic template. Permit reviewers look for site-specific engineering, and they start with the documents in front of them.

Permit timelines in Canada usually fall between 4 to 12 weeks, and more involved projects or busy municipalities can push that out to 16 weeks. If you want to avoid getting stuck in a slow back-and-forth, start the engineering and document prep early.

What permit reviewers expect to see

Reviewers check that the numbers on the drawings line up with the real site conditions. For a Canadian steel building, a complete submission usually includes:

P.Eng.-stamped drawings sealed by a Professional Engineer licensed in the province where the building will be erected
Site-specific climatic data tied to the exact postal code
The building’s stated importance category
Foundation design based on local soil and frost conditions
An Anchor Bolt Reaction Plan that coordinates the steel frame loads with the foundation design

The same issues tend to come up again and again when permit applications get flagged or rejected:

Requirement	Common Reason for Rejection
Manufacturing Standard	Manufacturer is not CSA-A660 certified
Engineering Authentication	Drawings stamped by an out-of-province engineer
Climatic Accuracy	Snow or wind loads taken from the wrong postal code
Structural Detail	Missing snow drift checks or unclear importance category
Foundation Alignment	Foundation drawings do not match the anchor bolt reactions

When one of these items is missing, review time can jump fast. A single revision cycle can add 2 to 6 weeks.

Provincial letters of assurance also need to be part of the package. That includes forms such as Ontario’s Schedule 1 or BC’s Schedule B, which confirm professional responsibility for the design. Province-to-province stamping rules matter too. For example, an Ontario P.Eng. stamp is not accepted in Quebec without OIQ membership.

How Canadian Buildings fits into the planning process

For planning purposes, Canadian Buildings helps Canadians find pricing, information, and a provider for customizable Canadian-made steel building kits before they move ahead.

Key points for owners comparing steel building options

Once your site loads are set, compare every quote on that same design basis. Price per square foot is only a rough starting point.

Here’s the issue: two quotes can show the same price and still refer to very different buildings. One may be designed for Toronto’s 1.0 kPa ground snow load, while another is based on Quebec City’s 3.5 kPa load. That difference matters. Rafter and column size, along with framing thickness, go up as loads go up.

What to confirm before moving ahead

Before you commit to a steel building package, confirm these details with the supplier:

Exact site location: Give the exact town or GPS coordinates so each quote uses the same design basis.
Stated kPa values: Ask for the snow, rain, and wind values in kPa so you can compare quotes directly.
Drift and unbalanced loads: Make sure the quote includes snow drift and unbalanced-load checks at steps, parapets, and valleys.
Frame thickness and member size: Check whether the quote uses a thinner frame or smaller members than your site loads call for.
Importance category: Confirm whether the building is classed as Low, Normal, High, or Post-Disaster importance. This changes design loads with a multiplier from 0.8 to 1.25.

That’s why two buildings with the same footprint can come in at very different prices. A generic quote can look fine on the surface, then fall apart once the actual site conditions are used.

City	Ground Snow ($S_s$)	Rain Load ($S_r$)	Wind Pressure ($q$)
Vancouver, BC	0.5 kPa	1.5 kPa	0.36 kPa
Toronto, ON	1.0 kPa	0.4 kPa	0.40 kPa
Ottawa, ON	2.1 kPa	0.5 kPa	0.40 kPa
Quebec City, QC	3.5 kPa	0.7 kPa	0.45 kPa
St. John’s, NL	2.8 kPa	1.0 kPa	0.55 kPa

Data sourced from NBCC Appendix C / Steel Calculator Reference.

Get the design criteria in writing before you sign. Wrong loads can trigger revisions, upgrades, and foundation changes.

FAQs

How do I find my site snow and wind loads?

Start with Appendix C of the National Building Code of Canada (NBCC). It lists the official climate data for locations across Canada, and those numbers are the baseline for code compliance.

From there, find your site’s reference data. That usually includes ground snow load, associated rain load, and basic wind velocity. You can get this through climate station locators or with help from a building professional.

It also helps to look beyond the base numbers. Site-specific factors can change the picture, including:

elevation
terrain
roof geometry
nearby obstructions

When do drifted snow loads control the design?

Drifted snow loads often govern the design when snow piles up unevenly due to wind, roof shape, or nearby obstructions. This matters most on flat or low-slope roofs, and around parapets, roof step-ups, mechanical units, and adjacent buildings.

In some parts of Canada, especially the Prairies and northern territories, drifting can become the main design driver. These local snow build-ups can exceed average roof snow loads, so they need to be calculated with care to help prevent structural deflection or even collapse.

Why can two same-size steel buildings be priced so differently?

Even when two steel buildings have the same dimensions, they may need different engineering based on where they’re being built and the climate rules set by the National Building Code of Canada.

For example, higher snow or wind loads can mean thicker steel, heavier framing, and extra bracing. Other factors matter too, including roof pitch, site exposure, elevation, and occupancy class. Each one can change the structural capacity the building needs – and, in turn, the final cost.