What are the snow load requirements for buildings in Central Oregon?

Why there is no county-wide number

Central Oregon spans high desert near Redmond and Prineville and the Cascade foothills west of Bend and Sisters. Snow differs a lot across that range. Deschutes County's building design criteria say it plainly: snow loads are sensitive to geographic location and elevation and must be determined for each project site, using the Oregon Snow Load Map.

That is why a garage kit sold with one snow rating may be fine on one lot and undersized on another a few miles away.

How to look up your snow load

The Oregon Building Codes Division publishes a how to guide for the 2021 Oregon Residential Specialty Code snow load map. The steps: go to the Oregon Snow Load Map lookup at snowload.seao.org, enter the site's latitude and longitude in decimal degrees, and select Get Snow Load.

The tool also reports the elevation it modeled. If that modeled elevation is greater than or equal to your actual project elevation, no adjustment is needed. If it is lower than your site's real elevation, the guide says the reported ground snow load must be adjusted upward.

The 36 psf minimum

For residential buildings designed with the code's prescriptive tables, the state guide says to use the greater of the mapped ground snow load and the code minimum of 36 psf. So even in the lowest snow parts of Central Oregon, prescriptive residential design does not go below 36 psf ground snow load.

Ground snow load is the starting point. Engineers convert it to a roof snow load using the roof's shape, exposure and other factors, and commercial buildings follow the Oregon Structural Specialty Code. The state's Oregon Design Criteria Hub also reports ground snow load for a location under both codes.

What this means for steel buildings

Steel garages and shops are where snow load questions come up most, because kits are often priced by snow rating. VersaTube describes its kits as engineered for the wind and snow loads of the area where they will stand. That only works if the order uses your site's real number, including any elevation adjustment.

A pole building supplier, Hansen Pole Buildings, makes a related point in its own blog: a buyer should not rely on an assumed rating, and should have sealed engineering drawings showing the design loads for the specific site. Whatever brand you buy, confirm the design snow load on paper before you order. See VersaTube steel buildings and VersaTube vs pole barn.

Snow load and the permit

Most garages, shops and steel buildings in Bend and Deschutes County need a building permit, and the permit review is where the design snow load is checked. Bring the site's snow load to the conversation with your builder and building department early, not after the kit arrives. See permits for a garage, shop or steel building.

Snow load questions to settle before you buy

Before you order any garage, shop or barn, get these answers in writing: What ground snow load did the map return for your exact site, and was it adjusted for elevation? What roof snow load and wind load is the building engineered for? Are sealed engineering drawings included for the permit? What foundation and anchoring does that engineering require? Who is responsible if the building department asks for changes?

If the answer to the first question is a single number for the whole region, keep asking. In Deschutes County, the answer is site specific.

Keeping the roof clear

Design load is what a building is built to carry, not a target to test. Drifts against walls, sliding snow from a higher roof and rain on snow can all add load in places. Keeping an eye on heavy accumulations and keeping doors and walkways clear is part of owning any building in Central Oregon.

Commercial buildings

Commercial and agricultural buildings follow the Oregon Structural Specialty Code rather than the residential code, and Deschutes County points commercial wind design to the OSSC and ASCE 7. The same principle holds: the snow load comes from the site, and an engineer turns it into the design load for that building.

Snow load reaches the ground

Roof snow travels down through the frame into the foundation. A building ordered for heavier snow usually needs heavier anchoring and footings, and those still have to sit below Deschutes County's 18 inch minimum frost depth. RCC pours foundations and erects metal buildings, so both are designed around the same number.