Frost and foundations
Washoe County's residential design criteria set a 24-inch frost line depth, which means footings should be below that depth so freezing soil can't lift them. NOAA's engineering weather data for the Reno airport records about 123 freeze-thaw cycles a year. Foundations built to code are below the frost line, but problems can arise with shallow footings on older additions, porches, steps and garages, or where water saturates soil and freezes against foundation walls. Frost heave can lift and crack shallow footings and slabs, and repeated freezing can widen existing cracks.
Dry soils and sudden water
The National Weather Service notes Reno's high-desert setting, and soils can be very dry for much of the year. When dry soils suddenly get wet, from a heavy storm, snowmelt, a broken irrigation line or a plumbing leak, some can lose strength or settle, while clay soils swell. Keeping water away from the foundation is the first line of defense: working gutters and downspouts, soil sloped away from the house, and irrigation that doesn't spray foundation walls.
Sloped lots
Many Reno-area homes are built on sloping lots in the foothills. Drainage on slopes needs particular attention, because water running downhill can collect against the uphill foundation wall or erode soil on the downhill side. Retaining walls, swales and drains help manage water. If a retaining wall near your house is leaning or cracking, have it evaluated, because a failing wall can affect the foundation.
Seismic considerations
Northern Nevada is seismically active, and Washoe County's design criteria place residential construction in a higher seismic design category. Older homes with unbolted sill plates or weak cripple walls in crawlspaces can benefit from seismic retrofits such as anchor bolts and bracing. Ask a foundation contractor or engineer whether your home has these vulnerabilities.
Basements and crawlspaces
Homes with basements or crawlspaces should be checked for water entry after snowmelt and storms. Cracks that leak can be sealed with injection, but drainage improvements usually need to come first.
Before you hire
Ask Reno foundation contractors what's causing the movement, whether frost or drainage is involved, which repair method they recommend, whether an engineer and permit are required, and what the warranty covers. Look up the contractor with the Nevada State Contractors Board before you sign.
Tracking cracks through the seasons
Frost and snowmelt can make cracks open and close through the year. Mark each crack's ends with a pencil and the date, photograph it beside a ruler, and check monthly. A year of records shows a contractor or engineer whether the movement is seasonal or progressing.
Additions and garages
Additions and detached garages sometimes sit on shallower footings than the main house and can move differently, opening cracks where old meets new. A thorough inspection should cover every part of the structure, not just the original house.