Snow Load Calculator
Estimate the weight of snow on your roof based on depth, density, and roof characteristics.
DISCLAIMER:
This calculator provides estimations only and should not replace professional engineering advice. For structural decisions or safety assessments, consult with a qualified structural engineer. Actual snow loads can vary based on multiple factors including wind drift, rain-on-snow events, and uneven distribution.
Snow Load Results
Snow Density: lb/ft³
Ground Snow Load: lb/ft²
Roof Snow Load: lb/ft²
Total Weight on Roof: lbs
Warning:
About Our Snow Load Calculator
Our Snow Load Calculator helps you estimate the weight of snow on your roof based on snow depth, density, roof characteristics, and local conditions. Understanding snow loads is crucial for ensuring structural safety during winter months, especially in regions with significant snowfall.
Why Snow Load Calculations Matter
Excessive snow accumulation can put dangerous stress on roofs and other structures. Each year, buildings collapse under heavy snow loads, often because the load exceeded the structure's design capacity. Our calculator helps you understand potential risk factors and when snow removal might be necessary.
How We Calculate Snow Loads
The calculator considers several key factors:
- Snow Depth: The measured depth of snow on your roof
- Snow Density: How heavy the snow is per cubic foot (varies by snow type)
- Roof Pitch: Steeper roofs hold less snow
- Exposure Factor: How exposed your roof is to wind (which can remove or pile up snow)
- Roof Area: The total area of your roof surface
The Snow Load Formula
The basic formula for calculating snow load is:
Snow Load (lb/ft²) = Snow Depth (ft) × Snow Density (lb/ft³) × Adjustment Factors
The adjustment factors account for roof pitch, exposure conditions, and other variables that affect snow accumulation and retention.
Understanding Snow Types and Density
- Light, Fluffy Snow (5-7 lb/ft³): Fresh powder snow that has just fallen
- Normal, Settled Snow (10-12 lb/ft³): Snow that has been on the ground for a few days
- Wet, Heavy Snow (15-20 lb/ft³): Snow with high moisture content or partially melted snow
- Icy, Compacted Snow (20-25 lb/ft³): Snow that has partially melted and refrozen
How Roof Pitch Affects Snow Load
Roof pitch is a critical factor in snow load calculations:
- Flat Roofs (0/12 pitch): Hold nearly 100% of fallen snow
- Slight Pitch (1/12 to 3/12): Hold approximately 70-90% of fallen snow
- Moderate Pitch (4/12 to 6/12): Hold approximately 50-70% of fallen snow
- Steep Pitch (7/12 to 12/12): Hold approximately 20-50% of fallen snow
- Very Steep Pitch (>12/12): Hold minimal snow, typically less than 20%
Warning Signs of Excessive Snow Load
- Sagging ceiling tiles or boards
- Cracked or split wood members
- Doors or windows that begin to stick or won't open
- Creaking, cracking, or popping sounds
- Severe roof leaks or visible deformations in the roof structure
If you observe any of these warning signs, consider having snow safely removed from your roof and consult with a structural engineer to assess potential damage.
Frequently Asked Questions
How do I measure snow depth on my roof safely?
The safest way to measure roof snow depth is from the ground using a long measuring stick or from a window that allows access to a portion of the roof. Never climb onto a snow-covered roof, as this is extremely dangerous. If you can't safely measure the roof snow depth, use the ground snow depth as an approximation, keeping in mind that snow often drifts and accumulates differently on roofs.
What snow load is considered dangerous?
Most residential roofs in snow-prone areas are designed to support at least 20-30 pounds per square foot of snow load. However, older structures or those in regions with historically little snowfall may have lower capacity. A snow load approaching 20 lb/ft² could be concerning for vulnerable structures. If you're unsure about your roof's capacity, consult with a structural engineer, especially if you're seeing any warning signs of structural stress.
Should I remove snow from my roof?
Snow removal should be considered when the estimated load approaches the design capacity of your roof structure or when you observe warning signs of excessive load. However, roof snow removal can be dangerous and may damage roofing materials if done improperly. For most cases, hiring professionals with proper equipment and safety training is recommended. If you choose to remove snow yourself, use a roof rake with an extension pole while standing on the ground, and never climb onto a snow-covered roof.
How does rain on snow affect the load?
Rain falling on snow can significantly increase the snow load in a short period. One inch of rain adds approximately 5.2 pounds per square foot of additional weight. Additionally, the rain can be absorbed by the snow, preventing drainage and further increasing the weight. Rain-on-snow events are particularly dangerous and often contribute to roof collapses. If rain is forecast when you already have significant snow accumulation, this should be treated as a high-risk situation.