Roof Load Calculator
Calculate the total live, dead, and snow load acting on a roof structure. For informational/educational use only.
Calculation Results
The combined weight per square foot acting on the roof rafters/trusses.
The total gravitational weight load acting on the entire roof surface area.
How This Calculator Works
To use the Roof Load Calculator:
- Enter the estimated Dead Load of the roof materials (typically 10-20 PSF for standard wood rafters and asphalt shingles).
- Enter the required Live Load (minimum construction and worker weight, standard is 20 PSF in many building codes).
- Enter the design Snow Load for your local climate zone (varies from 0 PSF in warm climates to 50+ PSF in northern regions).
- Specify the total sloped surface area of the roof.
- The calculator immediately calculates the total pressure load in pounds per square foot (PSF) and the total overall load weight in pounds.
Formula & Calculations
Total unit load is computed by summing the dead load, live load, and snow load:
Total Unit Load (PSF) = Dead Load + Live Load + Snow Load
To find the total gravitational force acting on the entire roof, we multiply the unit load by the total sloped roof surface area:
Total Roof Load (lbs) = Total Unit Load × Roof Surface Area
Disclaimer: This calculator provides informational estimates only. Exact roof loads and structural requirements must be verified by a licensed structural engineer or building inspector in accordance with local building codes.
Step-by-Step Calculation Examples
Standard Shingle Roof in Moderate Climate
Calculating roof load for a 1,500 sq ft asphalt shingle roof with 15 PSF dead load, 20 PSF live load, and a 10 PSF snow load.
- dead_load: 15
- live_load: 20
- snow_load: 10
- roof_area: 1500
- total_unit_load: 45.0 PSF (lb/ft²)
- total_load: 67500
Heavy Clay Tile Roof in Snow Area
Calculating load for a heavy tile roof with a 25 PSF dead load, 20 PSF live load, and a 30 PSF snow load.
- dead_load: 25
- live_load: 20
- snow_load: 30
- roof_area: 2000
- total_unit_load: 75.0 PSF (lb/ft²)
- total_load: 150000
Frequently Asked Questions
What is the difference between dead load and live load on a roof?
Dead load is the permanent, static weight of the roof structures and materials themselves (rafters, sheathing, underlayment, shingles, ceiling drywall). Live load is the temporary weight of workers, tools, and construction equipment during installation or maintenance.
How much does snow load affect a roof design?
Snow loads can be very significant. In cold climates, building codes require roofs to support snow loads ranging from 20 to 100+ PSF depending on historical snowfall. A heavy snow load requires thicker rafter lumber or closer truss spacing.
What is a typical dead load for asphalt shingles?
Asphalt shingles themselves weigh about 2 to 4 PSF. When combined with wood roof deck sheathing, underlayment, and rafters, the typical total dead load is estimated around 10 to 15 PSF.
What is the dead load of a clay tile roof?
Clay or concrete tile roofs are extremely heavy, weighing between 8 and 12 PSF on their own. The total roof dead load for tile installations is typically estimated between 25 and 30 PSF, requiring reinforced framing.
What is the standard residential roof design load?
A standard residential roof is usually designed to support a total load of 40 to 50 PSF. This is typically split into 15 PSF dead load, 20 PSF live load, and 10 to 15 PSF snow/environmental load.