When should I remove snow from my roof?

A conservative residential rule of thumb: clear snow when the calculated roof snow load (pf) reaches 20-30 PSF on a 20-25 PSF design roof, or any time you see structural warning signs — interior doors that suddenly stick, popping noises from the roof framing, new cracks in drywall, or visible deflection in the ceiling. Most modern residential roofs in snow country are designed for 30-40 PSF, and commercial flat roofs for 40-60 PSF; once measured load exceeds 75% of design capacity, get snow off promptly. Older homes built before 1980, mobile homes, and any unheated outbuilding should be cleared at lower thresholds (15-25 PSF measured load).

How does the ASCE 7-22 snow load formula work?

The simplified design snow load (pf) for a low-slope or flat roof is pf = 0.7 × Ce × Ct × Is × pg, where pg is the ground snow load (PSF, from the ASCE 7-22 map), Ce is the exposure factor (0.9 fully exposed, 1.0 partially exposed, 1.2 sheltered), Ct is the thermal factor (1.0 heated, 1.1 unheated, 1.2 cold-roof / well-vented), and Is is the importance factor (1.0 residential, 1.1 commercial, 1.2 critical facilities like hospitals and fire stations). For sloped roofs you then multiply by the slope factor Cs, which reduces snow load as pitch increases past 30 degrees on warm roofs and 15 degrees on cold roofs. Code-minimum design load is 20 PSF for residential occupancies regardless of calculated pf.

How much does a foot of snow weigh per square foot?

Snow weight depends entirely on density. Fresh dry powder (5-7 lbs/cu ft) gives roughly 0.5 PSF per inch — so 12 inches = ~6 PSF. Typical settled snow (10-14 lbs/cu ft) is about 1 PSF per inch — so 12 inches = ~12 PSF. Wet snow (15-20 lbs/cu ft) is closer to 1.5 PSF per inch — 12 inches = ~18 PSF. Old compacted snow with rain or ice layers (20-30+ lbs/cu ft) can hit 2-3 PSF per inch — 12 inches = 25-35 PSF. This is why a single 24-inch warm-and-wet New England nor’easter can stress a roof far more than 36 inches of Colorado champagne powder.

What is the difference between an ice dam and a snow load problem?

A snow load problem is purely about weight — too many pounds per square foot pressing down on the roof structure, risking deflection or collapse. An ice dam is about water management — heat escaping from the attic melts snow on the upper roof, water runs down to the colder eave, refreezes, and backs liquid water under the shingles into the wall and ceiling. You can have either or both. A roof rake removes snow from the lower 3-6 feet of roof to reduce both ice-dam formation AND eave load, which is often the highest-concentration zone for drifted snow. Heat cables only address the ice-dam side; they do not reduce snow weight.

How do I use a roof rake safely?

Always rake from the ground using a telescoping aluminum roof rake (12-24 ft reach). Pull snow downward in 2-3 ft swaths from eaves up to about 4-6 feet onto the roof — never try to clear the entire roof from the ground. Leave a 2-inch layer of snow on top of the shingles to avoid scraping granules off. Never climb onto a snow-loaded roof yourself — the surface is unpredictable, hidden ice is common, and your added weight can be the tipping point if the load is already near capacity. Stay clear of power lines (a wet aluminum pole conducts current). For roofs over 2 stories or pitches over 9/12, hire a professional snow removal service.

Does roof slope reduce snow load?

Yes. ASCE 7-22 applies a slope factor (Cs) that reduces design snow load as pitch increases. For warm roofs (heated buildings), Cs starts reducing at 30 degrees (about 7/12 pitch) and reaches zero around 70 degrees. For cold roofs (Ct = 1.1+), reduction starts at 15 degrees. A 12/12 metal roof in a heated home can have 50-70% of the flat-roof snow load — the snow slides off naturally. However, slid snow becomes a hazard at the eave, and any unbalanced load (windward bare, leeward drift) can be worse than a uniform load. Greenhouse-style steep arched roofs handle the most snow; flat commercial roofs the least.

What ground snow load should I use for my region?

Ground snow load (pg) values from the official ASCE 7-22 map: Florida and coastal Gulf states 0 PSF; Texas / Arizona desert 0-10 PSF; Mid-Atlantic (Virginia, Maryland) 20-30 PSF; Great Lakes and lower Midwest 25-40 PSF; New England (Massachusetts, Connecticut, Rhode Island) 40-60 PSF; Vermont, New Hampshire, inland Maine 60-100 PSF; Upper Peninsula Michigan and lake-effect zones 60-100 PSF; Mountain West (Colorado, Wyoming, Utah resort towns) 50-150+ PSF; Alaska 50-150+ PSF; coastal Pacific Northwest 15-40 PSF. Always confirm with your local building department — many counties publish official county-level pg values that supersede the ASCE map.

What roof load is dangerous for a residential home?

Most US residential roofs built after 1980 in snow regions are designed for 30-40 PSF of snow load. Loads over 40 PSF on a residential structure warrant active monitoring; loads over 50 PSF are an active risk and should be reduced. For older homes (pre-1970), mobile homes, agricultural buildings, and any structure with visible sagging or alteration history, the threshold is much lower — often 20-25 PSF. Commercial flat roofs are typically designed for 40-60 PSF but can be much higher in mountain regions. When in doubt, check the original architectural drawings or hire a structural engineer for a roof capacity assessment — a $400 inspection is cheaper than a collapse.

Will my homeowners insurance cover snow-related roof damage?

Most standard US homeowners policies (HO-3 and HO-5) cover sudden collapse from the weight of ice, snow, or sleet — but exclusions are common for gradual damage, ice-dam water infiltration where the dam formed over time, and damage to outbuildings or screened-in patios that have lower load limits. Roofs already in poor condition or past their service life are often partially or fully excluded. Document your roof condition with photos every fall, keep gutters and downspouts clear, and call your carrier BEFORE major work — emergency snow removal is sometimes reimbursable if you can show it prevented imminent loss. Read your specific policy carefully.

Should I install heat cables for snow load?

No — heat cables (heat tape, eave heaters) do not reduce snow load. They are specifically designed to melt channels through ice dams at the eave so meltwater can drain to the gutter instead of backing under shingles. They consume significant electricity (200-500 W per 100 ft) and address only the water-infiltration side of winter roof problems. For actual snow load reduction, your tools are: roof raking from the ground, professional snow removal, proper attic insulation (so heat doesn’t melt snow unevenly), and adequate soffit-to-ridge ventilation. Heat cables are a complement to those measures, not a substitute.

How do snow drifts and roof valleys multiply load?

A uniform pf calculation assumes snow lies evenly across the roof. In reality, wind, roof geometry, and adjacent taller structures concentrate snow into drifts that can be 2-4 times the uniform load. The highest-risk zones are: valleys between two roof planes (snow slides in from both sides), the leeward side of a ridge during prolonged wind, the lower roof beneath any adjacent taller wall or parapet, around HVAC units and chimneys, and the bottom 3-6 feet at every eave (sliding-snow accumulation). When you walk a snowy roof during inspection, the eave and valley accumulations are often where structural deflection or ice-damming will first show.

Does this calculator work for metric (kPa or kg/m²) units?

The calculator displays primary results in PSF (pounds per square foot, the US/Canadian convention) and also shows kPa (kilopascals, the SI/Eurocode/Russian standard) and kg/m² conversions for international users. Conversions: 1 PSF ≈ 0.04788 kPa ≈ 4.882 kg/m². So a 30 PSF design load ≈ 1.44 kPa ≈ 146 kg/m². The underlying ASCE 7-22 formula is dimensionally identical to the Canadian NBCC and Eurocode EN 1991-1-3 simplified expressions, so the same factors (exposure, thermal, importance) apply if you substitute the corresponding metric ground snow load value from your local code.

ASCE 7-22 Compliant · 2026 Edition

Roof Snow Load Calculator

Calculate the design snow load (PSF) on any roof using the official ASCE 7-22 formula pf = 0.7 × Ce × Ct × Is × pg. Get total roof weight, structural safety check, and a clear recommendation for snow removal — instantly, in your browser.

Design load

35.0

PSF (pf)

Total weight

35.00

tons on roof

Capacity used

117%

of 30 PSF

Risk level

CRITICAL

Active scenario

Custom Inputs

Quick Regional Presets

Ground Snow Load (pg)

PSF

From ASCE 7-22 map or local building department. See regional reference below.

Exposure Factor (Ce)

Typical suburban or wooded residential site — some sheltering on at least one side.

Thermal Factor (Ct)

Normal heated home or office — interior maintained 65°F or higher all winter.

Importance Factor (Is)

Homes, apartments, most office buildings — standard ASCE Risk Category II.

Roof Pitch (rise per 12 in run)

/12

Slope factor Cs = 1.000 · approx angle 26.6°

0 = flat, 4 = low slope, 6 = standard, 8-9 = steep, 12 = 45°. Steeper roofs shed snow naturally.

Roof Plan Area (sqft)

sqft

Horizontal projected area, not the slope-length. Use the footprint covered by the roof.

Assumed Roof Design Capacity (PSF)

PSF

Typical residential 25-40 PSF, commercial 40-60 PSF, mountain region 50-100 PSF. Check original drawings or engineer.

Design Snow Load (pf)

35.0PSF

1.68 kPa · 170.9 kg/m²

CRITICAL

CRITICAL: design load meets or exceeds estimated roof capacity. Stop occupying high-deflection rooms, remove snow professionally, and engage a structural engineer immediately.

Total snow on roof

70,000 lbs

35.00 tons

Capacity utilization

117%

vs 30 PSF design

Equivalent Snow Depths

If Wet Snow

23″

density ~ 15 lb/cu ft

If Dry Powder

70″

density ~ 6 lb/cu ft

ASCE 7-22 Formula Walkthrough

pg (ground)50 PSF

× 0.7 (constant)

× Ce (exposure)1.00

× Ct (thermal)1.00

× Is (importance)1.00

= flat pf (uniform)35.00 PSF

× Cs (slope)1.000

= design pf35.00 PSF

Understanding Roof Snow Load and Structural Safety

Roof snow load is the single most under-appreciated structural risk in cold-climate construction. A single wet February storm dropping 24 inches of high-density snow on a flat commercial roof can add 35 PSF of dead-weight load — more than 70 tons of additional weight on a 4,000-square-foot warehouse roof. That is the load that brings roofs down in the headlines every winter, and almost every collapse is preventable with five minutes of arithmetic and a couple of hours of snow removal.

The American Society of Civil Engineers publishes ASCE 7-22 (the current minimum design load standard adopted by the International Building Code and International Residential Code), which gives a clean, defensible formula for converting a region’s ground snow load into a roof design snow load. The simplified equation is pf = 0.7 × Ce × Ct × Is × pg, where pg is the ground snow load from the official ASCE map (or your local building department), and the three factors adjust for site exposure (Ce), how heated the building is (Ct), and how critical the occupancy is (Is). A sloped roof gets an additional reduction factor Cs because steep roofs shed snow naturally.

Ground snow loads in the United States range from zero across Florida and the Gulf Coast to over 150 PSF in the Colorado high country, the Sierra Nevada, parts of Alaska, and the Maine North Woods. New England and the lake-effect belts (Tug Hill, UP Michigan, Lake Erie shore) regularly see 60-100 PSF. Most US residential building codes set a minimum design snow load of 20 PSF regardless of ground value, but modern homes in snow country are designed for 30-40 PSF and commercial flat roofs for 40-60 PSF. Mountain homes can be engineered for 70-100+ PSF when local code requires it.

The danger zone for residential structures begins at a measured load of about 40 PSF (roughly 24-30 inches of typical settled snow). At that point a roof rake at the eaves is mandatory and professional snow removal should be scheduled. Above 55-60 PSF the structure is in active risk territory and a structural engineer should be consulted before the next storm. Commercial flat roofs have higher tolerances but are penalized by drift loads — snow blown off an adjacent taller roof can pile up at 2-4× the uniform load. Run this calculator before every major storm, save the result to your history, and treat the recommendation as a planning baseline, not a final engineering certification.

Snow Density Reference Table

Snow Type	Density (lb/cu ft)	Weight per inch	Typical Example
Fresh Dry Powder	5 – 7	~ 0.5 PSF	Champagne powder, Colorado/Utah dry storm
Typical Settled Snow	10 – 14	~ 1.0 PSF	Average mid-winter snow after 24-48 hrs
Wet New Snow	15 – 20	~ 1.5 PSF	Coastal nor’easter, lake-effect, spring storm
Compacted / Old Snow	20 – 30	~ 2.0 PSF	Multi-week accumulation, ski resort base
Snow with Ice Layers	30 – 50	~ 3.0 PSF+	Freeze-thaw cycles, rain-on-snow events
Pure Ice	57	~ 4.8 PSF	Solid ice dam or refrozen meltwater layer

Sources: USACE Cold Regions Research & Engineering Lab, ASCE 7-22 Commentary Chapter C7, NOAA Snow Density Climatology.

US & International Ground Snow Load Map Reference

Approximate ground snow load (pg) by region. Always confirm with your local building department — the ASCE 7-22 map has site-specific case-study (CS) zones in mountain regions where the official value can be 2-3× the map indication.

Region	Ground Snow Load (pg)	Notes
Florida & Gulf Coast	0 PSF	No design snow load — code minimum live load applies
Texas / Arizona Desert	0 – 10 PSF	Occasional event, code minimum 20 PSF usually governs
Mid-Atlantic (VA, MD, DE)	20 – 30 PSF	Heavy wet snow events; code minimum residential 20 PSF
Lower Midwest (KS, MO, IL)	20 – 30 PSF	Wide variance — check county map
Chicago / Detroit / Cleveland	25 – 35 PSF	Lake-effect zones can spike to 40+ PSF
Coastal New England (MA, CT, RI)	40 – 60 PSF	Heavy wet snow; commercial roofs at risk
Vermont / NH / Inland Maine	60 – 100 PSF	Highest sustained snow loads in lower 48 east
Northern Minnesota / Wisconsin	50 – 70 PSF	Cold dry snow but sustained 5-month accumulation
Mountain West (CO, WY, UT)	50 – 150+ PSF	Elevation-dependent; mountain town values often 75+ PSF
Lake-Effect NY / MI / PA	60 – 100 PSF	Tug Hill, UP Michigan, Erie snowbelts
Alaska (coastal & interior)	50 – 150+ PSF	Extreme variation by region; check borough code
Pacific Northwest Lowland	15 – 40 PSF	Cascade foothills jump significantly with elevation
Canadian Prairies	30 – 60 PSF (1.5 – 2.9 kPa)	NBCC equivalent; Calgary ~1.6 kPa, Winnipeg ~1.9 kPa
Canadian Maritimes	50 – 90 PSF (2.4 – 4.3 kPa)	Wet Atlantic snow; commercial cap rates often govern
Norway / Sweden / Finland	40 – 150 PSF (2 – 7 kPa)	Eurocode EN 1991-1-3; values increase rapidly with elevation
Northern Russia / Siberia	50 – 150 PSF (2.4 – 7 kPa)	SP 20.13330 standard; dry cold snow dominant
Hokkaido, Japan	60 – 200+ PSF (3 – 10 kPa)	Coastal sea-effect snow, highest in developed world

How to Use the Roof Snow Load Calculator

Five steps. Three minutes. No sign-up.

1
Find your ground snow load (pg)
Look up the ground snow load (pg) for your county using the ASCE 7-22 ground snow map, your local building department, or the regional reference table on this page. Enter that value in PSF — it is the single most important input.
2
Pick your exposure category
Choose Fully Exposed (open ridge / coastal / prairie with no nearby trees), Partially Exposed (typical wooded suburban), or Sheltered (dense conifer or downtown urban). Wind scours snow off exposed roofs; sheltered roofs accumulate more.
3
Identify the building type and thermal condition
Heated buildings (Ct = 1.0) shed snow faster from melt. Unheated garages and outbuildings (Ct = 1.1) hold more snow. Cold-roof construction and well-vented attics (Ct = 1.2) keep the deck cold and accumulate the most.
4
Set importance, slope, and roof area
Pick the ASCE Risk Category (residential / commercial / critical). Enter roof pitch as rise per 12 inches of run (0 for flat, 6 for typical, 12 for steep). Enter total roof area in square feet to get total snow weight in pounds.
5
Compare design load to roof capacity
The calculator returns the ASCE 7-22 design snow load (pf) in PSF, total weight in tons, and a four-level risk classification (Safe / Monitor / Warning / Critical) against the estimated roof capacity you entered. Act on the recommended action — rake, schedule removal, or call a structural engineer.

Real-World Use Cases

Pre-Storm Residential Risk Check

Run your home’s numbers in the fall before the first major storm of the season — save the result to history. When a 12-24 inch storm is in the forecast, you’ll instantly know whether to pre-rake the eaves or simply ride it out. Pair with our ice & water shield calculator to make sure your roof underlayment is sized for the meltwater that will follow.

Metal Roof Snow-Shed Planning

A 9/12-pitch standing-seam metal roof sheds nearly all dry powder, but the accumulated berm at the eave can hit 4× the uniform load. Use this calculator with our metal roofing calculator to spec snow guards, gutter heat tape, and properly anchored eave flashing.

Re-Roofing Material Selection

When tearing off an old asphalt roof in a snow region, the calculator helps you decide whether to upgrade to a heavier architectural shingle, switch to standing-seam, or add a second layer of ice-and-water shield. Cross-reference results with our asphalt shingle roofing calculator for total material weight and per-square cost comparisons.

New-Construction Framing Design

Before locking in rafter or truss spans for an addition or new build in snow country, plug the design load into this calculator and compare to common 2x10 / 2x12 capacity tables. Then use our rafter & framing calculator to verify member sizing, spacing, and the lumber order before breaking ground.

Pro Tips from Snow-Country Builders

Clear snow when design load exceeds 40 PSF residential

On a typical 25-40 PSF residential roof, plan removal once measured snow load hits 40 PSF (use this calculator). Rake the lower 6 feet at every eave first — that’s where drift, sliding snow, and ice dam pressure concentrate.

Watch valleys, drift zones, and lower roofs

A roof valley collects snow from two slopes at once. The lower roof of any L-shaped or split-level house collects drifted snow off the adjacent taller wall. These zones routinely run at 2-3× the uniform pf — inspect them first after every storm.

Attic ventilation is snow-load insurance

A well-vented attic keeps the roof deck near outdoor temperature, prevents irregular melt patterns, and reduces ice-dam formation. Aim for 1 square foot of net free vent area per 300 sq ft of attic floor, split balanced between soffit (low) and ridge (high).

Heat cables fix ice dams, not snow load

Heat cables (heat tape) at the eaves melt a drainage channel through ice dams so meltwater can reach the gutter. They do not reduce roof snow weight. Combine heat cables with annual roof raking and adequate insulation/ventilation for full winter resilience.

Photograph snow accumulation every major storm

A time-stamped phone photo from the same vantage point during and after every storm builds a year-over-year record that pays off in insurance claims and engineer consultations. Include a stick or yardstick in the frame for depth scale.

When in doubt, hire a structural engineer

A residential roof capacity assessment from a licensed structural engineer typically runs $300-600 and gives you a defensible number for your specific home. That’s cheaper than a single insurance deductible and an order of magnitude cheaper than a collapse.

Trusted by Northern Climate Pros and Homeowners

4.9

Based on 2,200 reviews

“Inland Maine ground snow load is 90 PSF, and my customers always think I’m exaggerating until I run this calculator with them on-screen. The structural concern flag at 60+ PSF design load is exactly the kind of plain-English warning that turns a "we’ll be fine" conversation into a "let’s rake the roof tonight" decision.”

Ethan Brodeur

Licensed Residential Builder · Bangor, Maine

February 14, 2026

“Used this on a remote project converting an old American cabin in Colorado where I needed a fast sanity check against my Eurocode background. The ASCE factors are clearly labeled, the kPa conversion is right next to the PSF number, and the snow density table is the best reference I’ve seen on any free calculator.”

Hanna Kallio

Structural Engineer · Helsinki, Finland

January 29, 2026

“I bid 20-30 commercial flat roofs a year and the importance-factor toggle (1.0 / 1.1 / 1.2) plus the total-weight-on-roof calculation gives me numbers I can show a building owner in two minutes. The "schedule snow removal" recommendation at over 40 PSF residential / 60 PSF commercial has helped me sell three winter service contracts already this season.”

Roger Vasilenko

Commercial Roofing Contractor · Minneapolis, MN

March 4, 2026

“After our neighbor’s barn collapsed under a wet February storm, my husband and I ran our farmhouse through this and realized the unheated attached garage was actually our weakest link, not the main house. Switched the building type from heated to unheated, watched the design load jump from 32 to 35 PSF, and finally understood why our garage drips during thaws. Booked a structural inspection that week.”

Marcie Therrien

Homeowner · Stowe, Vermont

February 22, 2026

Love using our calculator?

Roof Snow Load Calculator — Frequently Asked Questions

Have more questions? Contact us

Similar Calculators

More tools in the same category

Board and Batten Layout Calculator

Calculate board and batten spacing for perfect layouts

Feet and Inches Calculator

Add, subtract, and convert feet and inches measurements

Scale Calculator

Convert between different measurement scales for plans

Square Footage Calculator

Calculate room and area square footage accurately

Lumber Weight Calculator

Calculate lumber weight from species, dimensions and quantity. 17+ wood species, kiln-dried/green/pressure-treated moisture.

Cabinet Door Size Calculator

Calculate cabinet door dimensions for full overlay, partial overlay, or inset construction. Auto hinge count.

Often Used Together

Complementary tools for complete analysis

Calorie Intake Calculator

EV vs Gas Fuel Savings Calculator

Daily Compound Interest Calculator

Age Calculator

From Other Categories

Expand your calculations

Geometry and area calculations for building

Long Division Calculator Improper Fraction to Mixed Number Average Rate of Change Calculator

Measurement unit conversions

Grams to mL Converter mg to mL Converter Liters to kg Converter

Project cost and budget calculations

Daily Compound Interest Calculator Percent Off Calculator Pay Raise Calculator

Learn More

Dive deeper with our expert guides and tutorials related to Roof Snow Load Calculator

Loading articles...

Related Construction Calculators

Ice & Water Shield Metal Roofing Asphalt Roofing Framing

Roof Snow Load Calculator

Understanding Roof Snow Load and Structural Safety

Snow Density Reference Table

US & International Ground Snow Load Map Reference

How to Use the Roof Snow Load Calculator

Real-World Use Cases

Pro Tips from Snow-Country Builders

Trusted by Northern Climate Pros and Homeowners

Roof Snow Load Calculator — Frequently Asked Questions

Similar Calculators

Board and Batten Layout Calculator

Feet and Inches Calculator

Scale Calculator

Square Footage Calculator

Lumber Weight Calculator

Cabinet Door Size Calculator

Often Used Together

Calorie Intake Calculator

EV vs Gas Fuel Savings Calculator

Daily Compound Interest Calculator

Age Calculator

From Other Categories

Related Articles

Related Construction Calculators

Technical Services
59 toolsPopular

Power Tools⚡

Understanding Roof Snow Load and Structural Safety

Snow Density Reference Table

US & International Ground Snow Load Map Reference

How to Use the Roof Snow Load Calculator

Real-World Use Cases

Pro Tips from Snow-Country Builders

Trusted by Northern Climate Pros and Homeowners

Roof Snow Load Calculator — Frequently Asked Questions

Similar Calculators

Board and Batten Layout Calculator

Feet and Inches Calculator

Scale Calculator

Square Footage Calculator

Lumber Weight Calculator

Cabinet Door Size Calculator

Often Used Together

Calorie Intake Calculator

EV vs Gas Fuel Savings Calculator

Daily Compound Interest Calculator

Age Calculator

From Other Categories

Related Articles

Related Construction Calculators

Technical Services59 toolsPopular

Power Tools⚡

Technical Services
59 toolsPopular