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Snow Load Calculator

Construction

Estimate your roof's design snow load in psf from ground snow load, roof pitch, exposure, and thermal condition using a simplified ASCE-7-style method.

Reviewed by the thecalcu.com team · Last updated July 5, 2026

5100
060

Design Roof Snow Load

15
Flat Roof Snow Load
21

This calculator computes your Design Roof Snow Load, Flat Roof Snow Load from the values you enter.

Inputs
Ground Snow LoadRoof PitchExposure ConditionThermal Condition
Outputs
Design Roof Snow LoadFlat Roof Snow Load

What is a Snow Load?

A Snow Load Calculator estimates the design roof snow load, the weight per square foot that a roof structure must be engineered to support, from your local ground snow load, roof pitch, exposure condition, and building thermal status, using a simplified approximation of the ASCE 7 methodology used in US building codes. This figure is a critical input for structural engineers sizing trusses, rafters, and roof sheathing.

Snow load requirements vary dramatically by region and by a roof's specific characteristics, which is why the same ground snow load can translate into very different design requirements for a steep, exposed roof versus a flat, sheltered one. Pair this with the Roof Truss Calculator and Rafter Length Calculator for the framing decisions that snow load informs.

Why Use a Snow Load Calculator?

Understanding how ground snow load translates into an actual roof design load requires applying several adjustment factors together, pitch, exposure, and thermal condition, which is easy to get wrong without a structured calculation. This tool applies those factors consistently, giving you a preliminary design load estimate.

It's especially useful for exploring how design choices affect snow load, comparing a steep roof against a flatter design, or an exposed site against a sheltered one, shows how much these factors change the structural demand before finalizing engineering plans.

Who Should Use This Calculator?

Structural engineers and architects use this calculator for preliminary snow load estimates during early design, before finalizing calculations with full code compliance verification. Pole barn and outbuilding builders use it to get a rough sense of structural requirements for unheated structures in snow-prone regions. DIY shed and garage builders use it to understand roughly how much snow load their structure needs to handle. Building code officials and inspectors reference similar calculations when reviewing submitted structural plans. Homeowners in snow-prone regions use it to understand why their roof design includes a steeper pitch or additional structural reinforcement.

What Insights Does the Snow Load Calculator Give You?

The Design Roof Snow Load is the primary result, in pounds per square foot, this is the adjusted load figure accounting for your roof's specific pitch, exposure, and thermal condition, which structural engineers use for actual member sizing. The Flat Roof Snow Load result shows the intermediate figure before the pitch-based slope reduction is applied, useful for understanding how much your roof's steepness reduces the effective design load compared to a flat roof under the same ground snow load conditions.

How to use this Snow Load calculator

  1. Enter your Ground Snow Load in psf, find this value from your local building code or ASCE 7 hazard maps for your region.
  2. Enter your Roof Pitch in degrees.
  3. Select your Exposure Condition, fully exposed, partially exposed, or sheltered, based on your site's surroundings.
  4. Select your Thermal Condition, heated or unheated structure.
  5. Review the Design Roof Snow Load result, and verify it with a licensed structural engineer before finalizing any actual construction plans.
Show formula & methodology ↓Show less ↑

Formula & Methodology

The calculator applies a simplified ASCE 7-style approximation:

Flat Roof Snow Load = 0.7 × Exposure Factor × Thermal Factor × Ground Snow Load

Slope Factor = max(0, 1 − Roof Pitch ÷ 70)

Design Roof Snow Load = Flat Roof Snow Load × Slope Factor

Worked example: For a 30 psf ground snow load, 20° roof pitch, partially exposed site (1.0), and heated structure (1.0):

Flat Roof Snow Load = 0.7 × 1.0 × 1.0 × 30 = 21 psf

Slope Factor = max(0, 1 − 20 ÷ 70) ≈ max(0, 0.714) ≈ 0.714

Design Roof Snow Load = 21 × 0.714 ≈ 15 psf

This simplified estimate is useful for preliminary planning, final structural design should always be verified against your local building code's exact methodology.

Frequently Asked Questions

What is roof snow load?
Roof snow load is the weight of accumulated snow that a roof structure must be designed to support, typically expressed in pounds per square foot (psf). Building codes require roofs to be engineered for a specific design snow load based on the local ground snow load and the roof's own characteristics like pitch and exposure.
What is ground snow load?
Ground snow load is a baseline measurement, published by local building codes or ASCE 7 standards, representing the expected weight of snow accumulation on flat, unobstructed ground in a given region. It's the starting point for calculating the actual design load a specific roof needs to withstand, which is then adjusted for exposure, roof shape, and thermal conditions.
How does roof pitch affect snow load?
Steeper roofs naturally shed snow more easily than flat or low-slope roofs, so building codes typically apply a reduction factor to design snow load as pitch increases. This calculator applies a simplified slope reduction that decreases the design load as roof pitch angle increases.
What does 'exposure factor' mean in snow load calculations?
Exposure factor accounts for how wind affects snow accumulation on a roof, fully exposed roofs in windswept areas tend to have less accumulated snow (wind blows it off), while sheltered roofs surrounded by trees or taller structures can accumulate more snow, hence a higher exposure factor for sheltered conditions.
What does 'thermal factor' mean in snow load calculations?
Thermal factor accounts for whether a structure is heated, heated buildings melt some snow from below, reducing accumulation, while unheated structures (like detached garages or storage buildings) retain more snow and therefore use a higher thermal factor in the design load calculation.
Is this the same as a full ASCE 7 snow load calculation?
No, this calculator uses a simplified approximation of the ASCE 7 methodology for educational and preliminary estimation purposes, a full code-compliant snow load calculation for actual construction should be performed or verified by a licensed structural engineer familiar with your local building code amendments.
Why does my local building code matter for snow load design?
Ground snow load values and required design methodologies vary significantly by jurisdiction and are often amended from the base ASCE 7 standard by local building codes to reflect regional conditions, always verify the correct ground snow load value for your specific location from your local building department.
How does snow load affect truss and rafter design?
Design snow load is one of the key inputs structural engineers use when sizing roof trusses and rafters, since the structure must support this additional weight without excessive deflection or failure, see the [Roof Truss Calculator](/roof-truss-calculator/) and [Rafter Length Calculator](/rafter-length-calculator/) for related framing planning, though truss engineering itself requires this snow load figure as an input.
Also known as
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