Frost depth and footings
The City of Boise's adopted code amendments set a minimum frost depth of 24 inches for footings, so frozen soil can't lift them. NOAA's engineering weather data for Boise records about 78 freeze-thaw cycles a year. Foundations built to code sit below the frost line, but shallow footings on porches, steps, additions and detached garages, or slabs where water collects and freezes, can heave and crack.
Snowmelt and spring water
The National Weather Service describes Boise as semi-arid, with most precipitation falling from November through May, including around 20 inches of snow in an average year. When snow melts quickly, or rain falls on frozen ground, water can collect against foundation walls. That water increases pressure on basement walls, softens soil and finds its way through cracks. Downspouts that discharge well away from the house, soil graded away from the foundation and window wells with drains or covers are the first defenses.
Basement walls
Many Boise homes have basements. Horizontal cracks, stair-step cracks in block walls, and walls that bow inward point to soil pressure and need an evaluation. Vertical hairline cracks that leak can usually be sealed with injection. Bowing walls may need carbon fiber, steel bracing or wall anchors, and the drainage problem behind them should be fixed too.
Irrigation and dry summers
Boise's hot, dry summers mean most landscapes are irrigated. Irrigation lines near the house, sprinklers spraying the foundation, and broken lines can saturate soil next to footings. Aim sprinklers away from the house, check for leaks when the system starts up in spring, and keep moisture moderate near the foundation.
Newer subdivisions
Many homes in the Treasure Valley are in newer subdivisions built on graded and filled lots. Fill soils that weren't compacted well can settle in the first years after construction. If you notice new cracks or sticking doors in a newer home, document them and check whether a builder warranty applies.
Before you hire
Ask Boise 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's Idaho registration with DOPL before you sign.
Tracking cracks over a winter
Because frost and snowmelt can make cracks open and close with the seasons, it helps to track them through a full year before deciding on a major repair, unless the movement is clearly getting worse. Mark the ends of each crack with a pencil and the date, photograph it beside a ruler, and check monthly. Bring those records to any contractor or engineer; they show whether you're looking at seasonal movement or ongoing settlement.
Crawlspaces
Homes with crawlspaces should be checked for standing water after snowmelt, damp insulation, wood decay at the sill plate and posts that have shifted on their footings. A dry, ventilated crawlspace protects both the foundation and the framing.