Design Criteria for Residential Construction
One- and Two- Family Dwellings and Townhouses
Effective January, 1 2021
2018 International Residential Code, Parts I-VI and IX, appendices A, B and G (with State amendments).
2015 International Energy Conservation Code (with Idaho State amendments; 2012 IECC design)
2017 National Electrical Code (with State amendments)
- Wind Speed: 90 mph 3 sec. gust velocity
- Wind Exposure: “B” (“C” in some areas)
- Seismic Design Category: “B” (IRC Structures Only-See Commercial Design Criteria for IBC)
- Presumed Soil Bearing Pressure: 1500 psf without soils investigation
- Frost Depth: 24 inches
- Climate Zone: 5B
- Snow load: Ground snow load 15 psf. Minimum uniformly distributed design roof load shall be 25 psf per local ordinance
- Winter heating design temperature is 2 degrees (99% dry bulb)
- Table R301.5 is amended to require a minimum uniform live load of 40 psf in habitable attics and sleeping rooms.
- Foundations with stem walls shall be provided with a minimum of one # 4 bar at the top of the wall and one #4 bar at the bottom of the footing. #4 vertical bars are required at 6 feet on center.
- Basement walls to have one #4 horizontal bar at 4 feet on center. One #4 bar is also required horizontally and vertically around openings, extending 2 feet beyond the opening. One #4 bar to be placed diagonally at corners of openings subject to cracking. Vertical bars installed per IRC.
- Unvented fuel-burning appliances are not allowed.
- 30” minimum crawl space depth measured from bottom of floor joist (per local resolution)