Snow is the design problem
Spokane roofs are built for snow. NOAA's engineering weather data for Spokane lists a 50-year ground snow load of 42 pounds per square foot, a measure of how heavy snow on the ground can get in a severe winter; the design value for your house comes from the local building code. Roofs that are sound handle normal winters without trouble, but heavy, wet snow, drifting against taller walls and ice buildup at the eaves can stress older or poorly built roofs. If you see sagging, doors that start sticking in winter or cracks appearing in interior walls during heavy snow, have the roof and structure checked.
Ice dams
Ice dams are one of the most common winter roofing problems in Spokane. Heat escaping from the house melts snow on the upper roof, the water runs down to the cold eaves and refreezes, and the growing ridge of ice traps more meltwater, which backs up under shingles and leaks into walls and ceilings. Ice and water barrier along the eaves helps protect against leaks, but the cause is usually in the attic: missing insulation, air leaks from the house, or poor ventilation. When you get a roofing estimate, ask the contractor to inspect the attic and explain how they'd address ice dams at their source.
Avoid chipping ice off the roof with tools, which damages shingles. A roof rake used from the ground can remove snow from the lower part of the roof after heavy storms.
Freeze, thaw and flashing
NOAA's data also shows about 72 freeze-thaw cycles in an average Spokane year. Each cycle works on small gaps around flashing, pipe boots and chimneys. Annual inspections, ideally in late summer or early fall, catch those problems before winter.
Gutters and downspouts
Gutters filled with leaves and needles freeze solid and add to ice buildup at the eaves. Clean them in fall after the leaves drop, check that they're securely attached to handle the weight of snow and ice, and make sure downspouts discharge away from the foundation. Spokane's frost depth policy sets footings at 24 inches below grade, but surface water from downspouts that saturates soil near the foundation can still cause problems in basements and crawlspaces.
Metal roofing
Metal roofs shed snow well, which is one reason they're popular in snowy climates. Snow sliding off a metal roof can be dangerous to people, plants and anything below, so ask about snow guards over doors, walkways and lower roofs.
Before you hire
Ask Spokane roofers how they install ice and water barrier, how they'll address attic ventilation and insulation, whether they recommend snow guards, and whether the permit is included. Get it all in writing.
Timing
Roof replacement in Spokane is usually done between late spring and early fall, when shingles can seal properly. Book well ahead of fall, when demand peaks.