How do I calculate snow load on a roof?

Multiply the ground snow load (pg) by exposure, thermal, and slope factors per ASCE 7. The formula is pf = 0.7 × Ce × Ct × Is × pg for flat roofs, then adjust for slope.

What is the average snow load per square foot?

Ground snow loads range from 0 to over 100 psf depending on location. Most northern U.S. regions see design loads between 20 and 60 psf, as specified in ASCE 7 tables.

How much does wet snow weigh?

Wet, packed snow weighs roughly 15-20 pounds per cubic foot, compared to 3-5 pounds per cubic foot for fresh dry snow. A single foot of wet snow can exceed 20 psf on a roof.

When should I worry about snow load on my roof?

Be concerned when accumulated snow approaches your roof's design load, which is typically 20-40 psf for residential structures. Warning signs include sagging rafters, cracking sounds, and doors that suddenly stick.

Snow Load Calculator

Calculate roof snow loads based on ASCE 7 standards. Determine flat roof and sloped roof snow loads using ground snow load, exposure, thermal conditions, and building importance.

Ground Snow Load, pg (psf)

Roof Type

Roof Pitch (rise per 12" run)

Exposure Category

Thermal Condition (Ct)

Importance Factor (Is)

Results

Flat Roof Snow Load (pf)

28.0

psf

Sloped Roof Snow Load (ps)

18.7

psf

Design Snow Load

20.0

psf (governs)

Pitch Angle

26.6°

degrees

Slope Factor (Cs)

0.668

coefficient

Exposure Factor (Ce)

1.00

coefficient

Did this help?

How to Use This Calculator

Enter your local ground snow load (pg) in pounds per square foot. Select your roof type and enter the pitch as rise over 12 inches of run. Choose exposure, thermal, and importance categories. The calculator applies ASCE 7 coefficients to determine flat roof snow load and adjusts for slope.

Formula Used

Flat roof snow load: pf = 0.7 x Ce x Ct x Is x pg. Sloped roof snow load: ps = Cs x pf. Where Ce = exposure factor, Ct = thermal factor, Is = importance factor, Cs = slope factor, pg = ground snow load (psf).

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Disclaimer

This calculator is for estimation purposes only. Results may vary based on local conditions, materials, and building codes. Always consult a licensed professional before making decisions based on these calculations. MyContractorTools is not responsible for any errors or omissions.