Expert Take: Spokane County Snow Load Requirements and Roof Safety

Spokane County receives an average of 45 inches of snow per year, with some winters delivering significantly more. This snow creates substantial weight on roofing systems — weight that must be accounted for in building design and ongoing maintenance.

Understanding Snow Loads

Snow load is the weight of accumulated snow on a roof, measured in pounds per square foot (PSF). Two types matter:

Ground Snow Load: The weight of snow on flat ground — the starting point for calculations

Roof Snow Load: The adjusted weight accounting for roof slope, exposure, and other factors (typically lower than ground load)

Spokane Area Ground Snow Loads

• Spokane city: 30–35 PSF
• Spokane Valley: 30–35 PSF
• Cheney: 30–35 PSF
• Higher elevations (Mt. Spokane area): 50–80+ PSF
• Liberty Lake/Post Falls border: 35–40 PSF

*These values come from the International Building Code (IBC) and local amendments. Your specific location may require site-specific analysis.*

What These Numbers Mean

A ground snow load of 35 PSF means:

• 1 foot of fresh, dry snow weighs approximately 5–10 PSF
• 1 foot of wet, packed snow weighs 15–25 PSF
• Ice weighs approximately 57 PSF per foot

So a 35 PSF ground snow load could be reached with as little as 1.5 feet of wet, heavy snow — well within Spokane's normal winter range.

Building Code Requirements

Washington State building codes (based on IBC with local amendments) require:

1. Minimum design load must meet or exceed the ground snow load for your area
2. Roof slope factor reduces the design load for steeper roofs (snow slides off)
3. Drift and slide loads must be accounted for at roof transitions, valleys, and adjacent to taller structures
4. Unbalanced loads must be considered — wind can pile snow on one side of a roof

When Is a Structural Review Required?

A structural engineering review may be required when:

• Adding weight to the roof (e.g., solar panels, rooftop equipment)
• Changing roof geometry during renovation
• Converting attic space to living space
• The building predates modern snow load codes

Warning Signs of Snow Load Stress

Watch for these indicators during heavy snow events:

• Doors or windows that suddenly stick — indicates structural deflection
• Visible bowing or sagging of the roofline
• Cracking sounds from the attic or ceiling area
• New cracks in drywall, especially near the ceiling
• Water stains that appear during or after heavy snow (from ice dams caused by snow load deflection)

If you observe any of these signs, evacuate the area beneath the roof and call a professional immediately.

Safe Snow Removal

When snow accumulation approaches concerning levels:

When to Remove

• When accumulation exceeds 2 feet of dry snow or 1 foot of wet/packed snow
• When the roof is flat or low-slope (under 3/12 pitch)
• When drifting creates localized deep accumulation
• When ice dams are forming at eaves

How to Remove Safely

• Use a roof rake from the ground — never climb on a snow-covered roof
• Remove snow in layers — don't try to scrape to the shingles
• Leave 2–3 inches of snow on the roof to protect the surface
• Work from the eave upward to prevent avalanche risk
• Don't use salt or chemicals — they damage roofing materials

When to Call a Professional

• Snow depth exceeds safe roof rake reach
• Structural warning signs are present
• Ice dams have formed
• Drift accumulation against walls or higher roof sections

Roof Design for Snow Country

If you're building or replacing a roof in the Spokane area, consider:

1. Steeper pitch — 6/12 or greater pitch sheds snow more effectively
2. Metal roofing — snow slides off smooth metal panels (install snow guards to control release)
3. Engineered trusses — modern trusses are designed for specific snow load requirements
4. Snow guards — prevent dangerous snow avalanches on metal and smooth roofs
5. Reinforced structure — for areas with higher snow loads, additional structural capacity provides safety margin

Spokane's winter weather is serious, but well-designed and maintained roofs handle it safely season after season. Understanding your roof's capacity and watching for warning signs keeps your family safe during Eastern Washington's heaviest snowfalls.