Snow Load Calculator
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.
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.