How much snow can a roof hold?

Most residential roofs are designed to handle 20–40 lbs per square foot of snow load. Fresh light snow weighs about 3 lbs/sq ft per foot of depth. Packed wet snow weighs 20–21 lbs/sq ft per foot of depth. Ice weighs 57 lbs/sq ft per foot. Warning signs: cracking or popping sounds, sagging ceiling, doors that won't open, visible bending in structural members.

When should I remove snow from my roof?

Remove snow when it reaches 2 feet of light/fluffy snow, 1 foot of heavy wet snow, or any amount of ice. Also remove when you hear structural stress sounds (cracking, popping), see deflection in ceiling or rafters, or have a poorly maintained older roof. Use a roof rake from the ground — never climb on a snow-covered roof. Start from the eaves and work up.

What is the design snow load for my area?

Ground snow loads (Pg) vary significantly by location. ASCE 7 provides official ground snow load maps. Common values: Boston area: 30–40 psf. Chicago: 20–25 psf. Denver: 30–35 psf. Minneapolis: 35–45 psf. Buffalo: 40–50 psf. Seattle: 10–20 psf. Mountain areas: 50–300+ psf. Contact your local building department for the exact Pg for your location.

Does roof pitch affect snow load?

Yes — steeper roofs shed snow faster and accumulate less load. For pitches above 5/12 (22.6°), the slope factor Cs reduces the design snow load. At 12/12 pitch (45°), Cs = 0.5, meaning the design load is half the flat-roof load. Flat roofs and low-slope roofs hold the most snow — they require higher design loads and often benefit from heating cables at eaves.

Home / Roofing Calculators / Snow Load Roof Calculator

❄️ Snow Load Roof Calculator

Calculate roof snow load based on ground snow, pitch, and building type — and find out if your roof is at risk

Who Should Use This

Homeowners in snowy regions worried about roof capacity, those with flat or low-slope roofs, and anyone who has had unusual snow accumulation after a major storm.

Purpose

Calculate design snow load using ASCE 7 methodology, compare to typical roof capacity, and get a safety assessment with recommended actions.

Example

A flat roof in Buffalo, NY (Pg = 40 psf) has a design flat-roof snow load of Pf = 28 psf — which exceeds the typical 20 psf capacity of older construction, requiring snow removal.

Snow Load Details

Ground Snow Load (Pg) — lbs per square foot

Or Enter Custom Pg (psf) — leave 0 to use dropdown

Roof Pitch

Roof Thermal Condition (Ct)

Roof Exposure (Ce)

Roof Area (sq ft)

⚠️ Important: This calculator is for educational estimation only. For any structural safety concern, contact a licensed structural engineer immediately. If you hear cracking sounds or see sagging, evacuate and call emergency services.

Snow Load Results

Safety Assessment

—

Enter your details and click Calculate

Design Roof Snow Load (Ps)

— psf

Factored sloped-roof snow load

Calculation Details (ASCE 7)

Ground Snow Load (Pg)—

Flat Roof Factor (0.7 × Ce × Ct)—

Flat Roof Snow Load (Pf)—

Slope Factor (Cs)—

Design Load (Ps = Cs × Pf)—

Total Snow Weight on Roof—

Reference: Snow Load Capacity by Roof Type

Roof Construction	Typical Capacity
Modern engineered (post-1990)	30–50+ psf
Standard residential (1970–1990)	20–30 psf
Older residential (pre-1970)	15–25 psf
Flat commercial (steel deck)	20–40 psf
Wood frame flat roof	20–25 psf

How It Works

4 Steps to Your Snow Load Estimate

Find Your Ground Snow

Look up the ground snow load (Pg) for your area from the dropdown or local building department.

Select Roof Pitch

Choose your roof pitch — steeper roofs shed snow faster and have lower design loads.

Set Thermal & Exposure

Select building thermal condition and exposure — sheltered roofs accumulate more snow.

See Safety Assessment

Get your design snow load, total weight, and a safety assessment with recommended action.

Understanding the ASCE 7 Snow Load Formula

The standard method for calculating roof snow loads in the US is based on ASCE 7 (American Society of Civil Engineers Standard 7). The formula is:

Pf = 0.7 × Ce × Ct × Pg (flat roof snow load)

Ps = Cs × Pf (sloped roof snow load)

Where Ce is the exposure factor (0.9–1.2), Ct is the thermal factor (1.0–1.3), and Cs is the slope factor (0 to 1.0). The 0.7 factor accounts for the statistical probability that full ground snow doesn't always transfer to the roof equally.

Note that ASCE 7 also requires checking for unbalanced snow loads, drift loads at walls and parapets, and sliding snow loads — these are beyond the scope of this calculator and require professional engineering analysis.

Warning Signs of Roof Overload

Creaking, cracking, or popping sounds — structural distress; leave immediately
Visible sagging or deflection in ceiling, rafters, or ridge
Doors and windows sticking or failing to open/close properly
Cracks appearing in interior walls or ceiling drywall
Leaks appearing suddenly — ice dam or structural movement
Visible bending in roof structure visible from attic

If you observe any of these signs during heavy snow loading, evacuate the building and call a structural engineer or emergency services.

Safety Guide

Snow Load Safety — What You Need to Know

Prevention, removal, and when to call a professional

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Safe Snow Removal

Use a roof rake from the ground — never climb on a snow-covered roof. Start at the eaves and work toward the ridge. Leave 2–3 inches on the roof to avoid damaging shingles. Hire professionals for steep roofs or heavy accumulations. Never use a metal rake on metal roofing.

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Ice Dams

Ice dams form when heat escapes through the roof, melts snow, which runs to the cold eaves and refreezes. They block drainage and cause water backup under shingles. Prevention: proper attic insulation and ventilation. Treatment: calcium chloride ice melt (not rock salt), or professional steam removal.

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Heat Cables

Electric heat cables installed along eaves and in gutters prevent ice dam formation. Cost: $200–$800 installed for a typical home. Run on thermostats or manually during storms. Most effective on low-slope roofs prone to ice dams. Pair with improved attic insulation for best results.

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Annual Inspections

Before winter each year: inspect attic for any structural concerns, check that soffit and attic vents are clear, verify insulation is evenly distributed, check gutters and downspouts are clear. After major snowstorms: visually inspect from ground for unusual deflection or ice dam formation.

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Engineered Roofs

Homes built after 1990 in snow-prone areas are typically engineered to ASCE 7 standards for the local Pg. Check your original building permit — it should specify the design snow load. Pre-1970 homes in high-snow areas may be significantly under-designed by today's standards.

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Mountain & Rural Properties

Mountain properties may have Pg values of 50–300+ psf. Standard residential construction is not adequate — all mountain structures need site-specific engineering. A roof designed for 40 psf in the valley may need to handle 150 psf at 8,000 feet elevation. Contact your county building department for local Pg requirements.

Common Questions

Snow Load FAQ

Several sources for finding your Pg:

Local building department: Most reliable — call and ask for the ground snow load for your address
ASCE 7: The standard includes a US ground snow load map (Figure 7.2-1)
State building codes: Many states publish local amendments with specific snow load values
Structural engineer: Can calculate site-specific Pg for unusual locations (mountains, valleys)
Building permit: If your home was built with a permit, the design snow load should be on the structural drawings

Note: local Pg values can vary significantly within a county based on elevation. Mountain homes always need site-specific data.

Yes — flat roofs accumulate the highest snow loads and have the least capacity for shedding. General guidelines:

Remove when you've had more than 6 inches of wet snow or 12 inches of dry snow
Remove after any rapid freeze-melt-freeze cycle (creates ice, which is 5× heavier than loose snow)
Hire professionals for commercial flat roofs — personal injury risk is significant
After removal, check for and address any ice dam formation at drains or scuppers
Consider installing heat tape at drains to prevent freeze-over

Standard homeowners insurance covers sudden, accidental collapse from snow weight as a covered peril. Key points:

Collapse from snow load is typically covered under the "weight of ice, snow, or sleet" peril
Gradual sagging or deterioration is NOT covered — only sudden collapse
Document roof condition annually with photos for claims purposes
Some insurers in high-snow areas require proof of snow removal or maintenance
File a claim immediately if collapse occurs — delays can complicate coverage

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