Snow Load on Roof Calculator

What is a Snow Load on Roof Calculator?

A Snow Load on Roof Calculator helps you determine how much weight snow is putting on your roof. Heavy snow accumulation can cause structural stress or even roof collapse. This calculator estimates snow load using roof area, roof pitch, snow depth, and snow density.

Formula to Calculate Snow Load on Roof

1. Calculate Snow Load (psf or kN/m²)

$P_s=\frac{h_s\times {\rho }_s}{12}$

Where:

• $P_s$​ = Roof Snow Load (lb/ft² or psf)
• $h_s$​ = Snow Depth (inches)
• ${\rho }_s$​ = Snow Density (lb/ft³)

2. Adjust for Roof Pitch

For sloped roofs, snow tends to slide off more easily. We adjust the load by a pitch factor (Cₚ):

$P_{s,adj}=P_s\times C_p$

Where:

• $P_{s,adj}$= Adjusted Snow Load
• $C_p$​ = Pitch Factor (typically between 0.7 for steep roofs and 1.0 for flat roofs)

3. Calculate Total Snow Load on Roof

$W=P_{s,adj}\times A$

Where:

• $W$ = Total Snow Load (lb or kN)
• $A$ = Roof Area (ft² or m²)

Understanding Each Parameter

Example Calculation

Given:

• Roof Area = 1500 sq ft
• Roof Pitch = 25° (pitch factor $C_p=0.9$)
• Snow Density = 20 lb/ft³
• Snow Depth = 12 inches

Step 1:

$P_s=\frac{12\times 20}{12}=20\text{ psf}$

Step 2:

$P_{s,adj}=20\times 0.9=18\text{ psf}$

Step 3:

$W=18\times 1500=27,000\text{ lb}$

Final Result:

• Roof Snow Load: 18 psf
• Total Snow Load on Roof: 27,000 lb

Why It Matters

Calculating snow load helps ensure your roof’s structural safety. Builders use this data to determine whether reinforcements are needed and to comply with local building codes in snowy regions.

FAQs

1. What is a safe snow load for roofs?

Typically, residential roofs are designed to handle 20–40 psf, but it depends on local building codes and structure type.

2. How do I measure snow depth?

Use a ruler or yardstick to measure snow depth from the roof surface in multiple spots and take the average.

3. What affects snow density?

Wet snow is heavier (up to 30 lb/ft³), while fresh, dry snow is lighter (around 10 lb/ft³).

4. How can I reduce snow load on my roof?

Regularly remove snow using a roof rake or hire professionals for deep snow removal.

5. Does roof pitch reduce snow load?

Yes. Steeper roofs shed snow faster, lowering the effective snow load factor.