# Snow Load Calculator

Calculate roof snow load per ASCE 7 standards. Enter ground snow load, roof pitch, exposure, and importance factor.

## What this calculates

Determining the design snow load on a roof is critical for structural safety in cold climates. This calculator uses the ASCE 7 methodology to compute flat-roof snow load and apply slope reduction, exposure, and importance factors to arrive at the design snow load in pounds per square foot.

## Inputs

- **Ground Snow Load** (psf) — min 0, max 300 — Ground snow load (pg) from local building codes or ASCE 7 maps
- **Roof Type** — options: Flat / Low Slope (< 5°), Sloped — Flat roofs do not receive a slope reduction
- **Roof Pitch** (:12) — min 0, max 24 — Rise per 12 inches of run (used for slope reduction)
- **Exposure Category** — options: Sheltered (trees, buildings nearby), Partially Exposed (typical), Fully Exposed (open terrain) — How exposed the roof is to wind
- **Importance Factor** — options: Residential (Is = 1.0), Commercial (Is = 1.1), Essential Facility (Is = 1.2) — Building risk category per ASCE 7
- **Roof Area (optional)** (sq ft) — min 0 — Enter roof area to calculate total load in pounds

## Outputs

- **Roof Snow Load (pf)** (psf) — Flat-roof snow load before slope reduction
- **Sloped Roof Snow Load (ps)** (psf) — Snow load after slope reduction factor
- **Total Snow Load** (lbs) — Total weight of snow on roof (if area provided)
- **Equivalent Water Depth** (in) — Equivalent water depth of the snow load

## Details

The ASCE 7 formula for flat-roof snow load is: pf = 0.7 × Ce × Ct × Is × pg, where Ce is the exposure coefficient, Ct is the thermal factor, Is is the importance factor, and pg is the ground snow load from local data or ASCE 7 maps.

Sloped roofs receive a reduction based on the slope angle. For warm roofs with unobstructed slippery surfaces, the slope factor Cs equals 1.0 for pitches below about 30 degrees and decreases linearly to zero at 70 degrees. Steeper roofs shed snow more effectively, reducing the design load.

Ground snow loads vary dramatically by region: coastal areas may see 10-20 psf, while mountain regions can exceed 200 psf. Always use the ground snow load specified by your local building code or the ASCE 7 snow load map for your zip code. When in doubt, consult a structural engineer.

## Frequently Asked Questions

**Q: How do I find my ground snow load?**

A: Check your local building department or the ASCE 7 ground snow load map. Common values: Southeast US: 0-10 psf, Mid-Atlantic: 15-30 psf, Northeast/Great Lakes: 30-80 psf, Mountain West: 40-200+ psf. Many jurisdictions publish specific values by zip code.

**Q: Does roof pitch affect snow load?**

A: Yes. Steeper roofs shed snow more effectively. Pitches below about 6:12 (26.5 degrees) receive no slope reduction. Above that, the reduction increases linearly. Very steep roofs (above 14:12 or 70 degrees) are considered to shed all snow and have zero design snow load.

**Q: What is the importance factor for snow loads?**

A: The importance factor (Is) increases design loads for critical buildings. Residential structures use 1.0, commercial buildings use 1.1, and essential facilities (hospitals, fire stations, emergency shelters) use 1.2. This provides a safety margin proportional to the consequences of structural failure.

**Q: How much does snow weigh?**

A: Fresh light snow weighs about 3-5 lbs per cubic foot. Packed snow weighs 10-20 lbs per cubic foot. Wet heavy snow or ice can weigh 30-50+ lbs per cubic foot. One inch of water equivalent on a roof equals 5.2 lbs per square foot. Snow load is measured in PSF regardless of snow density.

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Source: https://vastcalc.com/calculators/construction/snow-load
Category: Construction
Last updated: 2026-04-21