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Snow Load Calculator | Flat & Sloped Roofs – ASCE 7, Eurocode & NBC

Free Snow Load Calculator for roofs – ASCE 7, Eurocode & NBC. Compute flat/sloped roof snow loads, drift analysis, Cs factor & more. Instant results.
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The Snow Load Calculator is a professional structural engineering tool designed to help engineers, architects, and builders quickly determine design roof snow loads according to major international standards.

It supports ASCE 7-22 (USA), Eurocode EN 1991-1-3, and NBC 2020 (Canada), with options for flat and sloped roofs (gable, hip, shed, curved), exposure factor (Ce), thermal factor (Ct), importance factor (Is), rain-on-snow surcharge, and snow guards.

Key features include:

  • Instant calculation of flat roof load (pf), sloped roof load (ps), slope factor (Cs), snow density, and equivalent depth
  • Unbalanced snow load and drift analysis
  • Interactive diagrams and step-by-step breakdown
  • Imperial (psf/ft) and Metric (kN/m²/m) units
  • Risk assessment with safety indicators

Whether you're designing a residential home or a commercial building, this free tool provides reliable preliminary snow load estimates to ensure structural safety. Always verify final results with a licensed structural engineer for code compliance and permitting.

Snow Load Calculator
Professional Structural Engineering Tool — ASCE 7 • Eurocode EN 1991-1-3 • NBC 2020
ASCE 7-22 Eurocode NBC 2020 Flat & Sloped Drift Analysis Free
Units:
💡 How to use: Enter your location's ground snow load, select roof parameters, and click Calculate. Results update instantly. All factors follow ASCE 7-22 by default.
📖 Building Code & Standard
Hospitals, fire stations = Cat IV; homes = Cat II
🏥 Ground Snow Load (p𝤑)
Refer to ASCE 7-22 Fig. 7.2-1 or local authority. Typical US values: 5–120 psf.
Above 1000 ft may require elevation correction
🏠 Roof Geometry
W = horizontal distance from eave to ridge
Slippery surfaces allow snow to shed → lower Cs for warm roofs
⚙️ Adjustment Factors
ASCE Table 7.3-1
ASCE Table 7.3-2
Auto-set from Risk Category above
→ If checked, slope reduction (Cs) is NOT applied
+5 psf if pg ≤ 20 psf and slope < W/50
🌬 Snow Drift Calculator (ASCE 7 Section 7.7)
Snow drifts form on the leeward side of obstructions, roof steps, and parapets. They can double or triple the uniform snow load and are a leading cause of roof collapse. Always check drift loads at level changes.
Length of roof upwind of the step or obstruction
Height of balanced snow on lower roof = p𝑓 / γ
Vertical distance between upper and lower roof
📚 Core Calculation Formulas (ASCE 7-22)
ASCE 7-22 Equation 7.3-1
\[ p_f = 0.7 \cdot C_e \cdot C_t \cdot I_s \cdot p_g \]
SymbolParameterTypical Range
pfFlat roof design snow loadpsf or kN/m²
CeExposure factor0.70 – 1.30
CtThermal factor0.85 – 1.30
IsImportance factor0.80 – 1.20
pgGround snow loadFrom ASCE 7 maps

The 0.7 factor converts from ground load to roof load, accounting for partial snow sliding and normal exposure.

ASCE 7-22 Equation 7.4-1
\[ p_s = C_s \cdot p_f \]
Slope Factor Cs (warm roof, slippery surface)
\[ C_s = \begin{cases} 1.0 & \theta \leq 15° \\ 1.0 - \dfrac{\theta - 15°}{55°} & 15° < \theta \leq 70° \\ 0 & \theta > 70° \end{cases} \]
Slope Factor Cs (warm roof, non-slippery)
\[ C_s = \begin{cases} 1.0 & \theta \leq 30° \\ 1.0 - \dfrac{\theta - 30°}{40°} & 30° < \theta \leq 70° \\ 0 & \theta > 70° \end{cases} \]
ASCE 7-22 Equation 7.7-1 (Imperial)
\[ \gamma = 0.13 \cdot p_g + 14 \quad \text{(not to exceed 30 pcf)} \]
Metric Equivalent
\[ \gamma = 0.426 \cdot p_g + 2.2 \quad \text{(kN/m}^3\text{, not to exceed 4.7 kN/m}^3\text{)} \]
Drift Height hd (ASCE 7-22 Fig. 7.7-1)
\[ h_d = 0.43 \cdot l_u^{1/3} \cdot (p_g + 10)^{1/4} - 1.5 \]

where lu = upwind fetch length (ft), pg in psf


Drift Width
\[ w = 4 \cdot h_d \]
Peak Drift Pressure (Triangular Load)
\[ p_d = h_d \cdot \gamma \]
Depth from Load
\[ h_s = \frac{p_s}{\gamma} \]

hs = equivalent snow depth (ft), ps = sloped roof load (psf), γ = snow density (pcf)

Windward Side
\[ p_{wind} = 0.3 \cdot p_s \]
Leeward Side (governs design)
\[ p_{lee} = I_s \cdot p_g \cdot \sqrt{h_d / p_g} \]

For simplified approach, leeward ≈ 1.5 × ps for slopes 2.4° to 30.2°

📊 ASCE 7 Factor Reference Tables

Exposure Factor Ce — ASCE Table 7.3-1

Terrain CategoryShelteredPartially ExposedFully Exposed
B (Urban/Suburban)1.01.11.2 – 1.3
C (Open Terrain)0.91.01.1
D (Coastal/Flat)0.70.80.9

Thermal Factor Ct — ASCE Table 7.3-2

Thermal ConditionCt
Heated structure (R ≥ 30 hr·ft²·°F/Btu)0.85
Heated structure (standard)1.00
Unheated, ventilated, or slightly heated1.10 – 1.20
Freezer buildings below 50°F1.30
Greenhouse with roof below 50°F1.30

Importance Factor Is — ASCE Table 7.3-3

Risk CategoryIsBuilding Type
I0.80Low hazard: Storage, agricultural, minor facilities
II1.00Standard: Most residential & commercial
III1.10Large assembly, schools >250, healthcare
IV1.20Essential: Hospitals, fire/police, EOCs

Typical Ground Snow Loads (pg) by Region

RegionTypical pg (psf)Typical pg (kN/m²)
Southern USA (mild)5 – 150.24 – 0.72
Midwest, Mid-Atlantic20 – 400.96 – 1.91
Northeast, Great Lakes40 – 801.91 – 3.83
Mountain West60 – 120+2.87 – 5.74+
AlaskaUp to 400Up to 19.1
Canada (south)15 – 500.72 – 2.39
UK / Western Europe5 – 300.24 – 1.44
Nordic Countries30 – 100+1.44 – 4.79+
📄 Export Calculation Report

Run a calculation first, then generate a formatted report summary you can copy, print, or save as PDF.

[ Run a calculation on the Basic Calculator tab first, then click Generate Report ]
✓ Copied to clipboard!
PDF Export Tip: Use your browser's Print dialog (Ctrl+P / Cmd+P) and select “Save as PDF”. For best results, set margins to “Minimum” and enable “Print backgrounds”.

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ⓘ Results are estimates based on ASCE 7-22 simplified procedures. Always verify with a licensed structural engineer for permit-required or safety-critical applications. Not a substitute for professional engineering judgment.

❄️

Snow Load Calculator — Complete User Guide

Step-by-step instructions, formulas, factor tables, FAQ, and expert tips for using our free structural snow load tool correctly and safely.

ASCE 7-22 Eurocode EN 1991-1-3 NBC 2020 Canada Imperial & Metric Free Tool

🏠 What Is a Snow Load Calculator? Purpose & Who Should Use It

A Snow Load Calculator is a structural engineering tool that estimates the weight of accumulated snow acting on a roof or structure. It converts environmental snowfall data (ground snow load, roof geometry, climate exposure) into design pressures that engineers and builders use to verify structural safety.

Our free online tool follows the ASCE 7-22 simplified procedure as its primary standard, with references to Eurocode EN 1991-1-3 and NBC 2020 (Canada). It is designed for:

User TypeUse CaseKey Tabs to Use
🏠 HomeownersCheck if roof needs snow removal todayBasic Calculator
🏭 Builders & ContractorsPreliminary load estimates before designBasic + Drift
📋 Structural EngineersVerify ASCE 7-22 load cases, drift surchargesAll tabs + Export
🏫 ArchitectsRoof shape comparison for new designsBasic + Formulas
🌋 StudentsLearn code-based snow load proceduresFormulas + Factor Tables

💥 Key User Pain Points & How This Calculator Solves Them

📚

❌ Complex building codes are hard to follow

ASCE 7-22 has dozens of tables and clauses. Solution: The calculator embeds all factor tables (Ce, Ct, Is, Cs) directly into dropdowns — you just select a description and the value is auto-applied.

🌞

❌ Hard to find the correct ground snow load

Pg varies wildly by location and is often buried in hazard maps. Solution: Enter your value from ASCE 7-22 Fig. 7.2-1 or your local authority; the tool accepts both imperial and metric inputs.

🔁

❌ Unit confusion (psf vs kN/m²)

Mixing imperial and metric leads to dangerous mistakes. Solution: A single toggle switch converts all inputs and outputs between psf/ft and kN/m²/m simultaneously.

🏱

❌ Drift loads are overlooked — the #1 collapse cause

Snow drifts at roof steps can double the local load. Solution: The dedicated Drift Analysis tab calculates hd, drift width, and peak pressure using ASCE 7 Section 7.7 formulas.

👀

❌ No visual feedback on load distribution

Numbers alone don't show where loads are heaviest. Solution: A live SVG roof diagram updates after each calculation, color-coding the snow depth and showing windward vs. leeward differences.

📄

❌ No shareable or printable output for permits

Engineers need formatted reports for submittals. Solution: The Export tab generates a text-based Calculation Sheet with all inputs, factors, and results that can be copied or printed as PDF.

🛠️ Step-by-Step User Guide: How to Use the Snow Load Calculator

💡 Before you start: Have your ground snow load value (pg) ready. In the USA, look up your location in ASCE 7-22 Figure 7.2-1 or at atcouncil.org. In Canada, use NBC 2020 Appendix C. In the UK/Europe, use EN 1991-1-3 or your national annex.
1

Select Your Unit System (Imperial or Metric)

Click the "Imperial (psf / ft)" or "Metric (kN/m² / m)" button at the top of the calculator. This changes all input labels and output values simultaneously. You only need to set this once.

⚠ Common mistake: entering a kN/m² value into a field set to psf. Always check the unit label next to each field.
2

Choose Building Code & Risk Category (Tab 1: Basic Calculator)

Under "Building Code & Standard", select your applicable code: ASCE 7-22 (USA), NBC 2020 (Canada), or Eurocode EN 1991-1-3 (Europe/UK). Then select your Risk Category (I–IV). The Importance Factor (Is) is set automatically.

⚠ Common mistake: selecting Category I for a school or hospital. Cat I is only for low-risk storage/agricultural buildings. Most homes = Cat II.
3

Enter the Ground Snow Load (pg)

In the "Ground Snow Load" card, type your site's pg value. This is the 50-year return period ground snow load from your applicable hazard map or local authority. Typical US values range from 5 psf (mild Southeast) to 120+ psf (mountain West).

⚠ Common mistake: using the current season's snow depth instead of the code-specified ground snow load. These are different — pg is a design value from hazard maps, not a measurement.
4

Define Roof Geometry

In the "Roof Geometry" card, set: Roof Type (flat, gable, hip, shed, curved), Roof Slope (select from list or enter custom degrees), Eave-to-Ridge Width W (horizontal distance from eave to ridge), Roof Length L (dimension parallel to the ridge), and Roof Surface Material (slippery = metal/glass; rough = shingles/tiles).

⚠ Common mistake: entering the rafter/slope length instead of the horizontal projection for W. W is measured on plan, not along the roof surface.
5

Set Adjustment Factors (Ce, Ct, Is)

Under "Adjustment Factors": select Exposure Factor Ce (based on terrain and roof exposure — more sheltered = higher Ce), Thermal Factor Ct (heated building = lower Ct; freezer = 1.30), and check the Importance Factor Is (auto-set by Risk Category). Also tick the checkboxes if snow guards are present or if you want to apply the rain-on-snow surcharge.

⚠ Common mistake: selecting "Fully Exposed" Ce for a roof in a dense urban area. An exposed suburban roof is typically Ce = 0.9; a sheltered urban roof can be 1.0–1.2.
6

Click "Calculate Snow Load"

Press the orange 🛠️ Calculate Snow Load button. Results appear instantly below including: flat roof load (pf), slope factor (Cs), design sloped roof load (ps), total roof weight, snow density, equivalent snow depth, unbalanced leeward load, and a risk badge (Low / Moderate / High / Critical).

7

Read the Live Roof Diagram & Breakdown

The SVG roof diagram updates to show your roof type with a color-coded snow layer — darker blue means heavier load. Click "Step-by-Step Calculation Breakdown" to expand a full walkthrough of every formula with your actual values substituted in.

8

Export Your Report (Optional)

Click the Export Report tab, then click "Generate Report". A formatted calculation sheet appears with all inputs, factors, results, and formulas. Click "Copy to Clipboard" to paste into a document, or use "Print / Save PDF" (Ctrl+P) to produce a formal calculation sheet.

STEP 1 Set Units STEP 2 Code + Risk STEP 3 Enter pg STEP 4 Roof Geometry STEP 5 Ce, Ct, Is STEP 6 Calculate! STEP 7 Read Results
Figure 1: Calculator workflow — follow steps left to right for a complete snow load analysis.

📝 All Formulas Used for Results Calculation

All calculations follow ASCE 7-22 Chapter 7: Snow Loads. Here is every formula the calculator uses, in the order applied.

① Flat Roof Snow Load — ASCE 7-22 Eq. 7.3-1
pf = 0.7 × Ce × Ct × Is × pg
  • pf = Flat roof design snow load (psf or kN/m²) — the primary result
  • 0.7 = Code-specified conversion factor (accounts for partial sliding and typical exposure)
  • Ce = Exposure factor (0.70–1.30, from ASCE Table 7.3-1)
  • Ct = Thermal factor (0.85–1.30, from ASCE Table 7.3-2)
  • Is = Importance factor (0.80–1.20, from ASCE Table 7.3-3)
  • pg = Ground snow load (psf or kN/m², from hazard maps)
② Sloped Roof Snow Load — ASCE 7-22 Eq. 7.4-1
ps = Cs × pf
  • ps = Design sloped roof snow load — the final design pressure used for structural checks
  • Cs = Roof slope factor (0.0–1.0, depends on slope, surface, and thermal condition)
  • pf = Flat roof snow load from Formula 1 above
③ Roof Slope Factor Cs — ASCE 7-22 Section 7.4
Warm roof, slippery surface:
Cs = 1.0 for θ ≤ 15°
Cs = 1.0 − (θ − 15) / 55 for 15° < θ ≤ 70°
Cs = 0 for θ > 70°

Warm roof, non-slippery surface:
Cs = 1.0 for θ ≤ 30°
Cs = 1.0 − (θ − 30) / 40 for 30° < θ ≤ 70°
Cs = 0 for θ > 70°
  • θ = Roof slope angle in degrees
  • A slippery surface (metal, glass, smooth membrane) allows snow to shed at lower slopes
  • If snow guards are present, Cs = 1.0 regardless of slope (snow cannot slide)
④ Snow Density γ — ASCE 7-22 Eq. 7.7-1
γ = 0.13 × pg + 14    (not to exceed 30 pcf)
  • γ = Snow density (pcf — pounds per cubic foot)
  • pg = Ground snow load in psf
  • Metric equivalent: γ = 0.426 × pg + 2.2 kN/m³ (max 4.7 kN/m³)
⑤ Snow Drift Height & Surcharge — ASCE 7-22 Fig. 7.7-1
hd = 0.43 × lu1/3 × (pg + 10)1/4 − 1.5

w = 4 × hd

pd = hd × γ
  • hd = Drift height (ft) — height of triangular drift above balanced snow level
  • lu = Upwind fetch length (ft) — roof length upwind of the step or parapet
  • pg = Ground snow load (psf)
  • w = Drift width (ft) — horizontal extent of the triangular drift load
  • pd = Peak drift pressure (psf) at the base of the triangle, tapering to zero at width w
  • γ = Snow density from Formula 4
⑥ Equivalent Snow Depth
hs = ps / γ
  • hs = Equivalent snow depth (ft or inches)
  • ps = Design sloped roof load (psf)
  • γ = Snow density (pcf)
  • This tells you how deep the actual snow layer would be to produce this design load
⑦ Total Roof Snow Weight
Wtotal = ps × Aroof
  • Wtotal = Total snow weight on roof (lbs or kN)
  • Aroof = Roof plan area = W × L (ft²)
  • Note: W (eave-to-ridge) and L (roof length) are horizontal projections, not along-slope dimensions
⑧ Unbalanced Snow Load (Gable Roof) — ASCE 7-22 Section 7.6
pwindward = 0.3 × ps
pleeward ≈ 1.5 × ps    (simplified, for θ = 2.4°–30.2°)
  • Unbalanced loads apply only when slope is between approximately 2.4° and 70°
  • The leeward (downwind) side accumulates more snow due to wind redistribution
  • Always design for the worst case: leeward unbalanced load may govern structural design
⑨ Rain-on-Snow Surcharge — ASCE 7-22 Section 7.10
psurcharge = +5 psf
  • Applied when: pg ≤ 20 psf AND roof slope < W/50 (low-slope threshold)
  • Accounts for rainwater absorbed into the snowpack, significantly increasing its density
  • Metric: +0.24 kN/m²

🌧 Snow Density Reference Table — Know Your Snow Type

The weight of snow per unit area depends heavily on its type and age. Fresh snow is light and fluffy; compacted or wet snow is far heavier. Ice buildup is the most dangerous — over 15 times denser than fresh snow.

Snow Density Comparison (kg/m³) Fresh 60 Damp 110 Settled 250 Wind-pkd 375 Very Wet 750 Ice 917 ⚠ 15x denser than fresh snow!
Figure 2: Comparative snow density — ice is the most hazardous and should be removed immediately.
Snow TypeDensity (kg/m³)Density (lb/ft³ / pcf)Notes
Fresh Snow603.75Light, fluffy; low risk
Damp Fresh Snow1106.87Slightly wet; same-day fall
Settled Snow25015.61Few days old; compacted
Wind-Packed Snow37523.41Monitor closely
Very Wet Snow75046.82High risk — remove promptly
Ice91757.25CRITICAL — remove immediately
❌ Ice buildup is an emergency. At 917 kg/m³, even a thin ice layer exerts enormous loads. Remove ice immediately and never let it accumulate on gutters or roof edges. Chemical de-icers are more effective than chipping — avoid rock salt as it corrodes metal gutters and fasteners.

📊 Adjustment Factor Tables — Ce, Ct, and Is Explained

Exposure Factor Ce — ASCE 7-22 Table 7.3-1

Ce adjusts for how much wind scours snow off the roof. A fully exposed roof in open terrain accumulates less snow than a sheltered roof surrounded by trees or taller buildings.

TerrainFully ExposedPartially ExposedSheltered
B — Urban/Suburban0.901.00 – 1.101.20 – 1.30
C — Open Terrain0.70 – 0.800.901.00
D — Flat / Coastal0.700.800.90
⚠ Higher Ce = more snow accumulates (roof is sheltered from wind). Lower Ce = wind removes snow.

Thermal Factor Ct — ASCE 7-22 Table 7.3-2

Ct accounts for heat loss through the roof. A heated building melts snow faster, reducing effective load. Freezer buildings keep snow frozen solid, increasing Ct.

Thermal ConditionCt
Heated (high insulation, R ≥ 30)0.85
Heated (standard residential/commercial)1.00
Slightly heated or ventilated attic1.10
Unheated (agricultural, garages)1.20
Freezer buildings (< 50°F interior)1.30

Importance Factor Is — ASCE 7-22 Table 7.3-3

Risk CategoryIsTypical Buildings
I — Low Risk0.80Storage sheds, minor agricultural, low-occupancy
II — Standard1.00Most houses, offices, apartments, retail
III — High1.10Schools, assembly (>300 occupants), nursing homes
IV — Essential1.20Hospitals, fire/police stations, emergency operations

🏱 Snow Drift Analysis Tab — The #1 Collapse Risk

❗ Critical safety note: Snow drifts at roof steps, parapets, and adjacent structures are the leading cause of roof collapses in snow regions. Always run a drift check whenever your building has level changes or obstructions.

When wind blows across a roof, it carries snow and deposits it on the leeward (downwind) side of any step, parapet, or obstruction. This triangular drift load can be 2–4 times higher than the uniform balanced load and acts over a concentrated width.

How to use the Drift Analysis Tab:

1

Enter Ground Snow Load (pg)

Same value as used in Basic Calculator. This drives the snow density calculation γ.

2

Enter Upwind Fetch Length (lu)

This is the horizontal length of the roof on the upwind side of the step or parapet. More upwind fetch = more snow available = larger drift. Use ft (imperial) or m (metric).

⚠ Common mistake: using the full roof length. lu is only the upwind portion — from the upwind eave to the step/parapet.
3

Enter Balanced Snow Height (hb)

The depth of uniform balanced snow on the lower roof before the drift is added. Estimate as: hb = pf / γ. You can get pf from the Basic Calculator results.

4

Enter Height Difference (h)

The vertical distance between the upper and lower roof surfaces. The drift height hd cannot physically exceed this value minus hb.

5

Click Calculate Drift

Results show drift height (hd), drift width (w = 4×hd), peak drift pressure (pd = hd × γ), and a visual cross-section diagram of the triangular drift load distribution.

Balanced Load (pf) Drift Peak (pd) Drift Width w = 4h𝑑 Upper Roof Lower Roof h𝑑
Figure 3: Triangular drift load profile at a roof step — the peak pressure (pd) occurs at the step and tapers to zero over width w.

🔄 Units, Input Validation & Common Mistakes to Avoid

ParameterImperial UnitMetric UnitConversion
Ground / Roof Loadpsf (lb/ft²)kN/m²1 psf = 0.04788 kN/m²
Snow Densitypcf (lb/ft³)kN/m³1 pcf = 0.15709 kN/m³
Length / Widthftm1 ft = 0.3048 m
Snow Depthinchesmm1 in = 25.4 mm
Total Forcelbs / tonskN1 lb = 0.004448 kN
Roof Slopedegrees or x:12degrees or %4:12 = 18.4° = 33.3%

Top 7 Input Mistakes & How to Avoid Them

#MistakeEffectFix
1Using observed snow depth as pgSeverely underestimates design loadUse code hazard map value, not a ruler
2Wrong unit system (kN/m² in psf field)Off by 20x — catastrophic errorCheck unit toggle before entering any value
3Slope length instead of horizontal WOverestimates roof area slightlyW = horizontal distance; use plan dimensions
4Wrong Risk Category (Cat I for a school)Underdesigned for actual occupancy riskConfirm with local building official or architect
5Ignoring drift loads at roof stepsMost common cause of partial collapsesAlways run Drift Analysis tab for stepped roofs
6Ce = "Fully Exposed" in dense suburbsUnderestimates load by 20–40%Suburban partially-exposed roof = Ce 0.9–1.0
7Snow guards checked off unintentionallySets Cs = 1.0; conservative but wastefulOnly check if physical snow guards are installed

🚨 Warning Signs — When to Remove Snow Immediately

Even if the calculator shows a load within code limits, certain physical signs demand immediate action regardless of numbers:

❄ Ice Buildup

Any ice layer on the roof surface or gutters. Ice is 15× denser than fresh snow and must be removed immediately. Never chip with metal tools — use chemical de-icers (not rock salt).

🚧 Sagging Ceiling or Roof

Visible deflection in ceiling tiles, rafters, or the roofline indicates structural stress. Evacuate the structure and contact a structural engineer before re-entry.

🔴 Cracking Sounds

Loud pops, creaks, or cracking from the roof structure are overload warnings. Treat as an emergency — do not enter the building until cleared by an engineer.

💦 Damp Spots / Leaks

Water stains on ceilings can indicate ice dam formation or structural movement allowing water infiltration. Address snow and ice immediately.

🚪 Doors & Windows Sticking

Difficulty opening internal doors or cracked door/window frames can signal structural racking due to snow load. Investigate promptly.

☀️ Solar Panels Covered

Snow on solar panels blocks generation. Remove carefully with a soft-bristled roof rake — do not use metal tools that can scratch panels or damage wiring.

✅ Safe Snow Removal Tips: (1) Use a roof rake from ground level where possible. (2) Never push snow over the edge where people may be below. (3) Leave a thin layer (1–2 inches) to avoid damaging tiles. (4) Secure ladders before climbing. (5) Avoid rock salt near metal gutters, nails, or flashing.

ⓘ Accuracy Note & Disclaimer

This calculator provides preliminary estimates based on simplified procedures from ASCE 7-22. Results are for guidance only and are not a substitute for a full engineering analysis by a licensed structural engineer (PE/SE). Site-specific conditions — including soil conditions, local ordinances, unusual roof geometries, and jurisdictional amendments — may require additional analysis beyond the scope of this tool. Always consult a professional for permit-required projects or safety-critical structural assessments. The 50-year ground snow load (pg) values vary by exact site location and elevation; values from this tool should be verified against the applicable hazard tool or local authority having jurisdiction (AHJ).

❓ Frequently Asked Questions (FAQ)

The ground snow load (pg) is the weight of snow on flat, open ground, measured at a specific location for a 50-year return period. It comes from hazard maps (e.g., ASCE 7-22 Figure 7.2-1). The roof snow load (ps) is the adjusted load actually acting on the roof surface after accounting for exposure (wind removes some snow), thermal effects (heat melts some snow), building importance, and roof slope (steeper roofs shed snow). Typically ps = 40–70% of pg for heated buildings with sloped roofs.
USA: Use the ATC Hazards tool at hazards.atcouncil.org and enter your address — it reports the ASCE 7-22 ground snow load (psf). Alternatively, refer to ASCE 7-22 Figure 7.2-1. Canada: See NBC 2020 Appendix C — 1-in-50-year snow load by city. UK/Europe: Use EN 1991-1-3 and your country's National Annex, which provides characteristic ground snow load (sk). Australia: Use AS/NZS 1170.3. Always verify with your local building department as some jurisdictions have site-specific amendments.
Use whatever unit system matches your source data. In the USA, ASCE 7-22 publishes pg in psf — use Imperial. In Canada (NBC), Europe (Eurocode), Australia, and most other countries, use Metric (kN/m²). The calculator's unit toggle converts all inputs and outputs instantly — just make sure you set the toggle before entering any values.
Per ASCE 7-22 Section 7.3.4, the minimum design roof snow load is: if pg ≥ 20 psf, then pf,min = 20 × Is. If pg < 20 psf, then pf,min = pg × Is. The calculator checks this automatically and will flag when the minimum governs with a yellow alert. This prevents under-design in very low-snow regions.
Generally yes — the slope factor Cs decreases as slope increases, reducing the design load. However: (1) If snow guards are installed, Cs = 1.0 regardless of slope because snow cannot slide. (2) For cold/unheated roofs (Ct ≥ 1.2), the Cs reduction starts at a higher slope angle. (3) On gable and hip roofs, steep slopes create unbalanced loads where the leeward side has a larger load than the windward side — this can govern structural design even though the balanced load is lower.
Yes — absolutely. Any level change creates a drift risk. Wind blows snow off the upper roof and deposits it at the base of the upper wall on the lower roof. This is the most common cause of roof collapses in commercial buildings. Use the Drift Analysis tab to calculate the triangular drift surcharge (pd, hd, w). Design the lower roof structure for the combined load: balanced load + triangular drift load at the step location.
Solar panel arrays must be designed to support snow loads just like any other roof surface. Use the Basic Calculator with your roof slope angle (typically low for solar, 10–20°). Solar panels are typically a smooth, slippery surface — select "Slippery" for roof material. However, the racking structure holding the panels also creates drift pockets below and beside the array. Always check the panel manufacturer's load ratings and use the drift analysis if panels are installed mid-roof with bare roof sections adjacent. Remove snow promptly from panels to restore generation efficiency.
The calculator's core equations follow ASCE 7-22 (USA). However, the adjustment factors (Ce, Ct, Is) and the general formula structure are conceptually similar across major codes: NBC 2020 (Canada), Eurocode EN 1991-1-3 (Europe/UK), and AS/NZS 1170.3 (Australia). For Canadian projects: refer to NBC 2020 for your province-specific Ss and Sr values; the factor structure is analogous. For European projects: the Eurocode uses the shape coefficient μ instead of Cs, and the characteristic load sk instead of pg. The Formulas & Theory tab documents the reference equations for each code. For regulatory/permit purposes, always use the code required in your jurisdiction.

🛠️ Ready to Calculate? Use the Free Snow Load Calculator

Use the tool above for instant ASCE 7-22 compliant roof snow load calculations — no account needed, no fees, works on mobile and desktop.

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