Footings and frost
The City of Boise's adopted code amendments set a minimum frost depth of 24 inches for footings, and the city's residential design criteria use a 20 psf ground snow load. Deck footings should bear below the frost line so frost can't heave them. NOAA's engineering weather data for Boise records about 78 freeze-thaw cycles a year, and footings that heave lift posts unevenly and strain the ledger.
Snow on decks
The National Weather Service notes Boise averages around 20 inches of snow a year. Decks must be built for the local design snow load, and snow sliding off roofs onto decks can add concentrated weight. Use a plastic shovel on composite decking to avoid scratches, and avoid deicing salts on wood and composite, which can damage surfaces and corrode fasteners.
Summer sun
Boise summers are hot and dry. Wood decks gray and check in the sun and need regular refinishing. Composite in darker colors gets hot; lighter colors and shade help.
Ledger flashing
Snowmelt and spring rain find their way behind poorly flashed ledgers. A properly flashed ledger, through-bolted or fastened with structural screws, protects both the deck and the house.
Railings and stairs
Snow and ice make stairs slippery. Consistent risers, strong handrails and good lighting matter. Railings must meet local code.
Permits
Decks attached to the house or above certain heights need permits from the City of Boise or Ada County.
Before you hire
Ask Boise deck builders how deep footings will go, what snow load they'll design for, how they'll flash the ledger, which materials suit sun and cold, and whether a permit is needed. Look up the contractor's Idaho registration with DOPL.
Composite or wood in the Treasure Valley
Composite and PVC handle Boise's snow, freeze-thaw and dry summer heat without needing stain, but darker colors get hot in July and boards expand with summer temperatures. Wood costs less and stays cooler but needs cleaning and refinishing to resist checking and graying. Whatever surface you choose, the frame underneath, its lumber, joist protection, connectors and footings, decides how long the deck lasts.
Shade
Boise summers are hot and sunny, with a record high of 111°F. A pergola, shade sail or covered section makes a deck usable on summer afternoons. Any roof over a deck must be built for the local snow load, and attached covers need proper flashing at the house.
Annual check
Each spring, inspect the ledger, footings, posts, railings and stairs, look for frost movement and loose fasteners, and clean the deck.
Hot tubs
A hot tub on a deck adds a large concentrated load. The frame and footings under it must be designed for that weight, or the tub should sit on its own slab.