How to compute snow load on roof: fundamental vertical action for structural design (houses, industrial sheds, airports, stadiums) per ASCE 7-22 Section 7 USA, IBC International Building Code, and Eurocode 1 EN 1991-1-3:2003 EU. Formula: p = Cs * Ce * Ct * Is * pg (ASCE) or s = mu * Ce * Ct * sk (Eurocode), where pg/sk is ground snow load (psf or kN/m^2 by climatic zone), Cs/mu is roof slope shape coefficient (0.8 flat-30°, decreases above), Ce exposure factor (0.8-1.2), Ct thermal factor (1.0 standard, 0.85 heated), Is importance factor (1.0-1.2). Essential tool for structural engineers, architects, IBC building code compliance, sizing wood/steel rafters, residential mountain (Vail CO, Aspen CO, Stowe VT), industrial roofs (Detroit, Buffalo NY snowbelt), stadium roofs (US Bank Stadium Minneapolis, Lambeau Field Green Bay).

Snow load formulas Eurocode and ASCE 7

Roof snow load Eurocode: s = mu * Ce * Ct * sk (kN/m^2). sk characteristic ground snow value 50-yr return period. NTC 2018 Italy zones: I (Alps) sk=1.5 kN/m^2 ground; II (Po valley) sk=1.0; III (Sicily Sardinia) sk=0.6.

ASCE 7-22 USA: p = Cs * Ce * Ct * Is * pg, pg ground snow load (psf) per ASCE Figure 7.2-1 zones. Northeast snowbelt 30-50 psf, Mountain West 25-90 psf, Florida 0 psf. Cs slope factor varies 1.0 (low slope) to 0 (steep cold roof). Buffalo NY pg=40 psf, Boston pg=40 psf, Minneapolis pg=42 psf, Anchorage AK pg=60+ psf, Honolulu pg=0.

Shape coefficient mu/Cs: roof slope alpha. Eurocode duopitch/monopitch: mu1=0.8 alpha 0-30°; mu1=0.8*(60-alpha)/30 alpha 30-60°; mu1=0 above 60° (sliding). Valley/drift: mu2 = 0.8+0.8*alpha/30, max 1.6. Cylindrical (domes): mu = 0.2+10*sec(beta) capped 2.0.

Exposure factor Ce: 0.8 windy site (hilltop, ocean), 1.0 normal (residential), 1.2 sheltered (forest, urban canyon). Influences snow accumulation: exposed sites scoured (-20%), sheltered accumulated (+20%).

Thermal factor Ct: 1.0 standard cold roof (insulated, snow stays), 0.85 heated roof (excess interior heat melts snow from underside). Greenhouse Ct=0.7. Indoor pools Ct=0.7-0.85 ASCE 7-22 Table 7.3-3.

History and context

Snow loads on roofs studied systematically after Galtuer Tyrol Austria 1999 avalanche and French roof collapses winter 1999-2000 (Strasbourg Mall, Charleroi Belgium). Precursor standards: ASCE 7-95 first widely-adopted USA, ENV 1991-2-3 1995 EU, EN 1991-1-3:2003 today. Italy: DM 14/01/2008 NTC 2008, DM 17/01/2018 NTC 2018. USA major incidents: Hartford Civic Center collapse 1978 Connecticut (3000 sq ft cantilever space frame after ice accumulation), Kemper Arena Kansas City 1979 collapse mid-event, Metrodome Minneapolis 2010 collapse (snow + cold air pressure). USA snowbelt: Buffalo NY 100+ inches/year, Syracuse NY 124 in, Erie PA 100 in, Anchorage AK 75 in, Stowe VT 130 in. Industrial: National Mining Association safety roof loads, OSHA workers' protection. Engineering firms: STV Group NYC, AECOM Los Angeles, HNTB Kansas City sports stadium roofs. Research: SUNY Buffalo CRI Center for Restoration Investigation, Cornell University Ithaca NY snow research. Universities: MIT Boston, UMN Minneapolis, Michigan Tech Houghton MI cold-climate engineering. Code: IBC International Building Code 2024 references ASCE 7-22 Chapter 7. State variations: New York Code 2020, California Building Code Section 1608.

USA snow zones table per ASCE 7-22 Figure 7.2-1

• Florida, Gulf Coast: pg = 0 psf (no snow design)
• Atlanta GA, Memphis TN: pg = 5-10 psf
• Washington DC, Richmond VA: pg = 20-30 psf
• NYC, Philadelphia PA: pg = 30 psf
• Boston MA, Buffalo NY: pg = 40 psf
• Minneapolis MN, Milwaukee WI: pg = 42 psf
• Stowe VT (mountain): pg = 90 psf
• Vail CO, Aspen CO: pg = 100+ psf (mountain resort)
• Anchorage AK: pg = 60 psf, mountain 90+
• Roof slope 0-30°: Cs = 1.0 (full load)
• Roof slope 60°+: Cs = 0 (sliding)
• Ce exposed: 0.9 (open terrain)
• Ce sheltered: 1.2 (forested, urban)
• Ct thermal heated: 0.85
• Ct unheated: 1.2 (warehouses)
• Is Risk Cat IV: 1.2 (hospitals, fire stations)

Worked numerical examples

Example 1 - American single-family house Boston MA. ASCE Cat B suburban, pg=40 psf=1.92 kN/m^2 (Boston zone). Roof gable 30° pitch, Ce=1.0 normal exposure, Ct=1.0 standard cold roof. Cs=1.0 (slope < 30°). p=1.0*1.0*1.0*1.0*40=40 psf=1.92 kN/m^2 = 196 kgf/m^2. Roof area 100 m^2: F=192 kN=43 kips. Compliant Massachusetts State Building Code based ASCE 7-22.

Example 2 - American mountain home Vail Colorado. Cat II Risk, pg=100 psf=4.79 kN/m^2 (Vail high mountain). Roof gable 45° steep pitch (snow shedding), Ce=0.9 exposed (mountain), Ct=1.0. Cs=(60-45)/30*1.0=0.5 (slope reduction). p=0.5*0.9*1.0*1.0*100=45 psf=2.16 kN/m^2 = 220 kgf/m^2. Roof area 80 m^2: F=172 kN=38.7 kips. Steep pitch helps shed snow, but lower areas accumulate (drifting).

Example 3 - American industrial warehouse Detroit MI. Cat II, pg=30 psf=1.44 kN/m^2 (Detroit zone). Flat roof 5° low pitch, Ce=1.2 sheltered industrial park, Ct=1.0 unheated warehouse, Is=1.0 normal. Cs=1.0. p=1.0*1.2*1.0*1.0*30=36 psf=1.72 kN/m^2. Roof area 500 m^2: F=863 kN=194 kips. Steel HEA 240 beams, Pratt truss spans 20 m, sandwich panel insulated roofing per Michigan Energy Code.

Example 4 - drift accumulation valley roof. Pg=60 psf=2.87 kN/m^2 (Northeast mountain). Y-shape valley two slopes 15° + central valley. Ce=1.0, Ct=1.0. Cs valley accumulation = 0.8+0.8*15/30=1.2 drift coefficient. p_valley=1.2*1.0*1.0*1.0*60=72 psf=3.45 kN/m^2 (60% over normal). Valley area 50 m^2: F=172 kN=38.7 kips concentrated! Snow guards or heating cables critical to prevent ice dam formation Northeast US winter.

Example 5 - dome stadium US Bank Stadium Minneapolis. ASCE Cat IV (essential facility), pg=42 psf=2.01 kN/m^2 (Minneapolis), Is=1.2. Cylindrical dome r=100 m, height 60 m, semi-angle 30°. Ce=1.0 urban, Ct=1.0. mu = 0.2+10*sec(30°)=0.2+11.55=11.75 (clamp 2.0 max ASCE/Eurocode). p=2.0*1.0*1.0*1.2*42=101 psf=4.84 kN/m^2 (peak coronal accumulation zone). Critical area 100 m^2: F=484 kN=109 kips. Cable+steel structure ETFE membrane, snow heating system US Bank.

Limits and considerations

1. Quasi-static model ignores dynamic effects (sudden ice accumulation falls).
2. Asymmetric loading: secondary wind creates +30% one-side asymmetric distribution.
3. Drifting snow: adjacent tall roofs offload snow to lower roofs, local accumulation up to mu=2.0.
4. Sliding snow: roofs >30° pitch release gradually, but injure pedestrians below.
5. Ice load: ice density 900 kg/m^3 vs snow 200, load 4.5x same volume (ice dams Northeast US).
6. Total load: combine snow + wind + seismic per ASCE 7-22 LRFD load combinations.
7. Rare events (100-yr blizzard): return periods >50 yr require importance factor adjustment.
8. Climatic change: warming reduces snow frequency but increases short intense events.
9. Large roofs (>1000 m^2 industrial): spatial load variation, effective area reduced.
10. Light structures (industrial sheds): high load/structure ratio, cyclic fatigue critical.

Common errors

1. Wrong climatic zone: USA varies dramatically (Florida 0 to Vail 100+ psf).
2. Using ASCE 7-22 outside USA: Eurocode uses different coefficients format.
3. Cs=1.0 above 30° slope: drops linearly 1.0 to 0 between 30°-60° per ASCE 7-22 Section 7.4.
4. Neglecting valley roofs: mu up to 1.6, accumulation 2x normal.
5. Ct=1.0 always: greenhouses Ct=0.7, indoor pools Ct=0.7-0.85.
6. Confusing snow load with snow water equivalent (SWE measurement vs loading).
7. Neglecting drifting: snow falling from adjacent tall roof onto lower one accumulates.
8. Not updating existing structures post-2022: ASCE 7-22 zones updated post climatic data.
9. Using mu cylindrical for domes: clamp 2.0 max ASCE 7-22 Section 7.6.
10. Ignoring importance factor Is for hospitals, schools, fire stations (Risk Cat III/IV = 1.1-1.2).

Numbered applications

1. Mountain residential: Vail CO, Aspen CO, Stowe VT chalets, IBC + ASCE 7-22.
2. Industrial warehouses: Detroit MI, Buffalo NY, Cleveland OH snowbelt structures.
3. Agricultural barns: Wisconsin Iowa Minnesota dairy barns, snow load on hay storage.
4. Ski resorts: Aspen Vail Park City UT lift stations, gondola buildings, lodges.
5. Stadiums and arenas: US Bank Stadium Minneapolis (dome 2016), Lambeau Field Green Bay open-air.
6. Airport hangars: Anchorage AK, Salt Lake City UT, Denver CO heated hangars Ct=0.85.
7. Solar photovoltaic: roof anchoring SunPower Tesla Solar in Northeast NY MA snowbelt.
8. Glass roofs and skylights: greenhouses commercial agriculture upstate NY hydroponics.
9. Light modular roofs: tents temporary structures cold climate emergency shelters.
10. Educational: civil engineering courses MIT, Cornell, Michigan Tech, UMN.

For support

For technical questions or reports: info@calcoi.com. Educational tool for preliminary structural sizing. For professional design consult ASCE 7-22 Section 7 USA snow loads, IBC International Building Code 2024, AISC American Institute Steel Construction Steel Manual 16th ed, ACI American Concrete Institute 318-19, NDS National Design Specification wood, AISI North American Specification cold-formed steel. FEMA P-2090 snow loads. SUNY Buffalo CRI restoration. Cornell snow research. Michigan Tech cold climate engineering.

Updated July 2026