A snow load rating tells you how much weight per square foot your roof is engineered to carry, measured in pounds per square foot (psf). It is not a national number — it is set locally, driven mainly by your elevation and your region’s real snowfall history, which is why the same building style can need a very different rating two counties apart.
Northcraft’s standard published buildings are engineered to a basis of ground snow load up to 35 psf. If your site needs more than that — and in a lot of the country, it will — that is one of Northcraft’s five “what moves the price” factors, not a reason your project cannot be built. Here is what the rating actually measures and how to read one.
Ground snow load vs. roof snow load: not the same number
This is the single most misunderstood part of a snow load rating. Ground snow load is the weight of snow measured on the ground in your area, based on historical data for your location. Roof snow load is what your actual roof is designed to carry, and it is calculated from the ground number, then adjusted up or down by several factors specific to the building itself.
Those adjustment factors are why two buildings on the same lot, with the same ground snow load, can have different roof design requirements:
Exposure factor. A roof exposed to wind on an open site can shed more snow than a sheltered roof in trees or between other structures, which can reduce the design load.
Thermal factor. An unheated storage building holds snow longer than a heated, conditioned space, where some snow melts off — heated buildings can sometimes use a lower design factor for this reason, unheated ones cannot.
Roof slope. A steeper roof sheds snow faster than a low-slope roof, which factors into the final design number.
Importance/risk category. A building where failure would be more consequential — occupied space vs. simple storage — can carry a higher required safety margin.
This is why “what psf do I need” does not have a single answer even for one address — it depends on what kind of building you are putting there.
Where these numbers actually come from
In the United States, snow load design values trace back to ASCE 7 (the structural engineering standard referenced by most state and local building codes), but a lot of states and counties do not rely on ASCE 7’s national hazard maps alone — mountain and high-elevation areas in particular often use their own county-specific tables or a state structural engineers association’s own published report, because elevation changes snow load so dramatically over short distances that a national map cannot capture it accurately. That is exactly the pattern you will see on our Colorado state page, where the real published table runs from the Front Range up through mountain-elevation counties, each with its own documented figure — we deliberately do not repeat that table here, since the real numbers belong on the page built to carry them, sourced county by county.
Why elevation matters more than latitude
A common assumption is that snow load tracks how far north you are. It does not, not reliably. Elevation is usually the bigger driver within a single state — a low-elevation valley floor and a high-elevation mountain community in the same county can carry very different design snow loads, sometimes by a wide margin. This is why a single statewide number is often misleading, and why the real state pages on this site present snow load as a range tied to elevation bands or specific counties rather than one figure for the whole state.
Idaho is one of the clearest examples: the University of Idaho’s own published study puts ground snow load at around 15 psf in Boise and as high as 243 psf at Schweitzer Basin — the same state, driven almost entirely by elevation. Our Idaho state page documents the full range city by city. Oregon and Washington tell a related version of the same story from opposite sides of the Cascades. Our Oregon state page covers a fixed 20 psf statewide minimum that climbs sharply, and by site-specific lookup rather than one published number, toward the Cascades; our Washington state page documents a specific real range for the same terrain, from about 20 psf in Seattle to 433 psf at Snoqualmie Pass. Utah’s own statewide code table shows the identical pattern on a smaller scale, from 21 psf in St. George to 67 psf in Monticello — see our Utah state page for the full table.
When you need more than Northcraft’s standard basis
If your site’s required ground snow load is above Northcraft’s published basis, your building still gets built — it just gets engineered to your real number, which is one of the five factors that can move the price on a specific project (the other four are eave height above basis, wind load above our published threshold, collateral load on I-beam buildings, and high seismic activity). We do not publish the dollar amount each factor adds, because it depends on how far above basis your specific site sits — but we do tell you which factors apply to your project and why before you order. See our states pages for Wyoming, Montana, and Maine for three more examples of how elevation- and region-driven snow load gets documented for a real location — Maine’s heaviest confirmed towns run up to 100 psf — or see the full list of states we currently publish on our steel buildings by state page.
What happens if a roof is underrated for its real snow load
This is not a hypothetical risk in heavy-snow regions — roof collapses from underrated structures are a real, recurring cause of property loss after major snow events. A roof designed to the wrong number does not fail gradually with warning signs; it can fail suddenly under sustained load, particularly with wet, heavy snow late in the season. This is exactly why your local building department checks your stamped engineering drawings against your real, local snow load requirement before issuing a permit — see our permit requirements article for how that review works.
How to find your real number
Your local building department is the authoritative source for the design snow load required at your specific address — not a national map, and not a generic “zone” estimate. When you get a quote from us, we confirm your real ground snow load, wind speed, and applicable code edition with your local jurisdiction before finalizing your engineered drawings, rather than estimating it. Call us at (888) 460-9294 or email estimating@northcraftsteel.com and tell us your address — we will tell you what your building actually needs to be rated for.