Metal Building Wind Load in Spokane County: 110 mph Design Speed, Exposure Category and Big Doors (2026)

Spokane County's building permit packet lists a 110 mph design wind speed, and every metal building we put up is engineered for it. But the number on the permit form is only the starting point. Where your shop sits, what surrounds it, how big the doors are and whether you leave them open on a windy day all change how hard the wind pushes and pulls on the frame. Here's what Spokane-area owners should know before ordering a pre-engineered metal building (PEMB).

How windy does it actually get here?

The Inland Northwest gets several windstorms most winters, and the National Weather Service's Spokane office says a typical local windstorm brings gusts in the 50 to 60 mph range. The big ones go higher:

• November 17, 2015: Spokane International Airport gusted to 71 mph, the strongest non-thunderstorm gust on record there. Around 396,000 Avista customers in eastern Washington and north Idaho lost power
• January 13, 2021: another 71 mph gust at the airport
• June 21, 2005: the airport's highest peak gust on record since 1984, 77 mph, during a thunderstorm

Those are airport readings. Open ridges, the West Plains and wide farm fields can see stronger gusts than town.

What the 110 mph number means

Washington builds to the International Building Code, and the IBC sends wind design to the ASCE 7 standard (Minimum Design Loads for Buildings and Other Structures). ASCE 7's basic wind speeds are 3-second gusts measured 33 feet above open ground, mapped as a design-level event rather than a typical storm. That's why the design speed is well above the gusts people actually remember.

Spokane County's residential design criteria table lists:

• Wind speed: 110 mph
• Ground snow load: 39 psf, with a 30 psf minimum roof snow load
• Frost line: 24 inches
• Seismic design category: C (parts of the unincorporated county may qualify as B)

Your building's engineer takes the 110 mph figure and adjusts it for your site's exposure, the building's height and shape, and how enclosed it is.

Exposure category: why open acreage matters

ASCE 7 sorts every site into an exposure category based on what the wind crosses before it reaches your building:

• Exposure B: urban and suburban areas or wooded land with lots of closely spaced obstructions the size of a house or bigger. For a building with a mean roof height of 30 feet or less, that roughness has to extend at least 1,500 feet upwind
• Exposure C: open terrain with scattered obstructions generally under 30 feet tall, including flat open country and grasslands. This is the default wherever B or D doesn't apply
• Exposure D: flat, unobstructed areas such as open water, mud flats and salt flats, extending at least 5,000 feet upwind

A shop in a Spokane Valley subdivision may qualify as Exposure B. A shop on open acreage near Cheney, Reardan, Davenport or the Palouse edge is usually Exposure C, which means higher design pressures on the same building. A wheat field or a cleared pasture doesn't count as "obstructions," so don't assume rural trees will get you to B.

Big doors change the math

Shops and RV buildings have huge openings, and ASCE 7 cares about them. It classifies buildings as enclosed, partially enclosed or open based on how the wall openings are distributed. A building with one wall full of large openings can be classified as partially enclosed. That pushes the internal pressure coefficient from plus or minus 0.18 for an enclosed building to plus or minus 0.55 for a partially enclosed one, which means much more uplift on the roof and more outward pull on the walls.

What that means for your building:

• Tell us how you'll use the doors. If big doors will often be open, or you want an open-sided bay, the engineer can design for it
• Order wind-rated doors. Door makers label garage and overhead doors for design wind pressure (see DASMA's wind load labeling data sheet). The door needs to match the pressures on your building's drawings
• Close doors in a storm. A building designed as enclosed is relying on those doors staying shut

Where wind load shows up in a metal building

• Frames and bracing: the main frames, rod or cable bracing and portal frames resist wind pushing on the walls and roof
• Anchor bolts and footings: uplift and sideways shear go down through the columns into the foundation. That's why the anchor bolts and footings have to match the manufacturer's column reactions. See our PEMB anchor bolt guide
• Panels and fasteners: roof corners and edges see the highest suction. Fastener spacing and panel type come from the engineering. Our panel guide covers PBR, R-panel and standing seam
• During erection: a partly built frame is at its weakest. Temporary bracing stays in until the permanent bracing and sheeting are on, which is one reason we watch the forecast on crane days

How Raven handles it

Every building we supply comes with stamped engineering for your site's wind, snow and seismic loads. We look up your parcel before we quote, ask how you'll use the doors, and set the anchor bolts ourselves to the manufacturer's drawings. Raven isn't tied to one manufacturer, so we source each building from whoever can deliver the engineered package fastest.

Raven's going rate for an installed pre-engineered metal building is about $60 to $75 per sq ft. Electrical, plumbing and utility hookups are not included and are extra. Door upgrades and site work are quoted for your project.

For the rest of the planning picture, see our Spokane County snow load guide, our roll-up vs. sectional door guide and our roof pitch guide.

Get a metal building quote

Call 509-350-2016 or request a free quote with your building size, door layout and address or parcel number. See our steel building services.

Sources

• Installed pricing: Raven Buildings' current going rate
• Spokane County BP-06, Residential Building Permits (design criteria)
• NWS Spokane: Spokane Record High Wind Speeds
• NWS Spokane: The Historic Wind Storm of November 17, 2015
• NWS Spokane: The Weather Watcher, Winter 2015 (PDF)
• American Wood Council: Definitions of Exposure B, C and D
• Bentley: ASCE 7-10 and ASCE 7-16 Exposure Categories
• Bentley: Wind load definitions, ASCE/SEI 7-16 and 7-22 (enclosure classification)
• DASMA Technical Data Sheet 1502: Garage Door Wind Load Labeling (PDF)