Roof Load Calculator
Structural roof load analysis determines whether a roof system can safely support the combined weight of materials, occupants/workers, snow, and wind forces. This calculator follows the load combination methodology referenced in ASCE 7 and the International Building Code (IBC).
Roof Parameters
Dead Load (Permanent Weight)
Live and Environmental Loads
This is a simplified load analysis. ASCE 7 requires additional factors for exposure, thermal, importance, and drift. A licensed structural engineer should perform the official load analysis for permitting and design.
Understanding Roof Loads
Dead Load
Dead load is the permanent weight of the roof structure itself — roofing material, sheathing, framing, and insulation. This is constant and does not change with weather. Typical residential dead loads range from 8–15 PSF for asphalt shingles to 25–35 PSF for slate or concrete tile.
Live Load
Roof live load accounts for temporary loads during construction, maintenance, and repair. The IBC specifies a minimum of 20 PSF for most roofs, reducible to 12–15 PSF for steep pitches (over 4/12) with specific tributary area conditions.
Snow Load
Roof snow load is derived from ground snow load using the formula:
pf = 0.7 × Ce × Ct × Is × pg
Where Ce (exposure), Ct (thermal), and Is (importance) are typically 1.0 for standard residential construction. The 0.7 factor converts ground snow to flat roof snow. Pitched roofs get further reduction based on slope.
Wind Uplift
Wind creates upward suction on roofs. Estimated uplift pressure uses a simplified version of ASCE 7:
q = 0.00256 × V² × Kz × G × Cp
Where V is the 3-second gust speed in mph. Uplift acts opposite to gravity loads and is critical for connection design (hurricane clips, straps).
Frequently Asked Questions
What is the maximum load a residential roof can hold?
Most residential roofs are designed for a total load of 40–60 PSF (dead + live combined). In heavy snow regions, total design loads may reach 80–100+ PSF. The actual capacity depends on rafter/truss size, spacing, span, and species grade.
How do I find my ground snow load?
Ground snow loads are mapped in ASCE 7 Figure 7.2-1 and adopted by local jurisdictions. Your local building department can provide the design snow load for your area. Common values: 10–20 PSF (Southeast), 20–40 PSF (Mid-Atlantic), 40–80 PSF (Northern states), 80–200+ PSF (mountain regions).