Returns the ASCE 7-22 design snow PSF for your deck — the upstream input that feeds Joist Span + Beam Span + Deck Load + Ledger Bolt calculators. 50 state defaults per IRC R301.2(5), elevation adjustment for mountain sites, exposure factor (fully-exposed / partially-exposed / sheltered), importance category (Cat I residential through Cat III critical), and drift load math for decks downwind of higher roofs. Output: design snow PSF + controlling load tag showing whether IRC 40 psf live load, snow, or drift is driving your structural sizing.
0 = no upwind roof. Any positive value triggers drift load math per ASCE 7-22 §7.7.
ASCE 7-22 §7.3 flat-roof formula: Pf = 0.7 × Ce 1 × Ct 1.2 × Is 0.8 × Pg 25 = 17 psf flat-roof snow. No drift load adjustment.
Use 40 psf as the snow + live load input on Joist Span Calculator + Deck Load Calculator + Ledger Bolt Calculator. Snow PSF is below IRC R301.5 minimum 40 psf live — live load drives structural sizing.
Joist Span + Deck Load + Ledger Bolt all take snow load as an input. Enter 40 psf there to get structural sizing reflecting your local snow conditions.
ASCE 7-22 §7.3 flat-roof snow + IRC R301.2(5) state defaults. County-precise values from your local building department or the ASCE 7 Hazard Tool override the state default. Not a substitute for stamped structural engineer letter in extreme snow zones (60+ psf) or high-elevation sites (5,000+ ft).
How to use
50 US states + DC. The calculator uses the central-county ground snow value from ASCE 7-22 Table 7.2-1. If you live in a mountain or coastal county that's well above or below the state default, override using the elevation field or enter a custom ground snow PSF from your local building department.
Mountain and high-altitude sites get more snow. Rough ASCE commentary: add ~1 psf for every 100 ft above the state's typical elevation (around 800 ft baseline). Denver at 5,300 ft = +45 psf above the Colorado default. The calculator auto-adjusts.
Fully-exposed (open terrain, no trees, no buildings within 30 ft — Ce 0.9) — wind regularly clears snow. Partially-exposed (default for most suburbs — Ce 1.0) — typical baseline. Sheltered (dense trees, tight urban courtyard — Ce 1.2) — snow accumulates without wind disturbance, design for 20% more.
Freestanding-low + attached-elevated + rooftop all use thermal factor Ct = 1.2 (open structure — same as an unheated outbuilding). Covered + roofed decks drop to Ct = 1.0 (heated thermal envelope below). This matters in mid-snow regions where Ct gets you 17% less design snow.
Category I — Residential (Is = 0.8) is the default for single-family + multifamily residential decks per ASCE 7. Category II — Standard (Is = 1.0) for small commercial. Category III — Critical / Assembly (Is = 1.1) for hospitals + emergency facilities + assembly occupancies.
If your deck is downwind of a higher roof (a house roof shedding snow onto a lower deck below), drift load can add significant additional snow piling. Enter the height difference in feet — calculator estimates the additional drift PSF per ASCE 7-22 §7.7.
Bottom of results shows the controlling load — either the IRC R301.5 minimum 40 psf live load, your calculated snow PSF, or a drift load combined number. Use this as the snow load input on Joist Span Calculator + Deck Load Calculator + Ledger Bolt Calculator.
Material guide
Three honest paths. Composite wins the 25-year math for most homeowners, wood wins on upfront cost, and PVC is unbeatable around water. Each card below answers in one glance — recalculate the bill of materials by clicking a brand in the picker above.
How we calculate
The Snow Load Calculator returns the ASCE 7-22 design snow PSF for your deck — the upstream input that feeds every structural-sizing calculator on the site (Joist Span, Beam Span, Deck Load, Ledger Bolt). State-by-state ground snow defaults per IRC R301.2(5), plus the deck-specific projection (decks behave like flat roofs and catch full ground snow — they don't shed like sloped roofs). Inputs: state + optional county / elevation override, exposure category (fully-exposed / partially-exposed / sheltered) per ASCE 7-22 Table 7.3-1, importance category (most decks = Cat I residential), and an upwind-roof drift consideration for decks next to higher roof surfaces. Output: design snow PSF + a 'load controller' tag showing whether your structural sizing is driven by live load (IRC 40 psf minimum), snow, or drift. 2-3K/mo search volume — especially in northern + mountain states.
State ground snow defaults are central-county values from ASCE 7-22 Table 7.2-1 + IRC R301.2(5). Exposure factor Ce from ASCE 7-22 Table 7.3-1 (0.9 / 1.0 / 1.2). Thermal factor Ct = 1.2 for open decks, 1.0 for covered. Importance factor Is from ASCE Table 1.5-2. Drift load simplification from ASCE 7-22 §7.7 — county-precise drift requires full ASCE Hazard Tool lookup. For elevations above 5,000 ft or for mountain ski-region sites, always confirm with local building department.
Ce = exposure factor (0.9-1.2), Ct = thermal factor (1.0 covered / 1.2 open), Is = importance factor (0.8-1.1 residential to critical), Pg = ground snow PSF. The 0.7 multiplier converts ground snow to flat-roof snow per ASCE.
Above the state default elevation (around 800 ft baseline), add ~1 psf per 100 ft. Mountain sites in CO, UT, ID can be +50 psf above the state default. Always confirm with local building department for mountain elevations.
If deck is downwind of a higher roof, drift snow piles against the deck-adjacent wall. Simplified ASCE estimate: 1.5 psf per foot of height delta up to 60% of the flat-roof snow PSF. Real ASCE §7.7 is more complex — use this as a planning estimate.
IRC R301.5 mandates 40 psf minimum live load for residential decks regardless of snow. In southern states snow PSF is typically below 40 — IRC live controls. In northern states snow exceeds 40 — snow controls. Drift can push controlling load above either.
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