Deck builders in King County, WA

King County has about 1,003,284 homes, with a median construction year of 1983 (the Washington median is 1985). Within our covered ZIP codes — about 967,427 homes — the median is 1983, close to the county as a whole.

Homes in the covered parts of King County have a median construction year of 1983, so a deck original to a typical house would now be about 43 years old — beyond the point where wood framing, fasteners and flashing can be assumed sound.

Many decks from the 1970s and 1980s were built before today's detailed deck provisions appeared in model codes. Common issues on decks of this age include corroded hangers, posts set directly in soil and ledger boards fastened with nails. Replacement is often the better value than repeated repairs.

Oldest housing: Medina (1973), Mercer Island (1973) and Seattle (1974). In these communities, expect retrofit decks on older houses and aging decks that need structural inspection, ledger and flashing upgrades, or replacement. Newest housing: Maple Valley (1998), Bothell (1997) and Issaquah (1997). Here, projects lean toward enlarging builder-installed decks, adding stairs and railings, and upgrading to low-maintenance boards.

The nearest NOAA climate station with 1991–2020 normals is Seattle Sand Pt Wsfo. It records an average of 25 days a year with a low at or below 32°F — relatively few freezing nights. On roughly 24 of those days the temperature climbs back above freezing, so water in wood, soil and gaps between boards repeatedly freezes and thaws.

Frost is less severe in King County than in northern states, but footings still have to meet the local frost-depth requirement, and freeze-thaw cycles are enough to work loose nails and open checks in unsealed wood.

Snowfall is light — about 3.8 inches in an average year at Seattle Sand Pt Wsfo — so occasional ice is a bigger concern than snow load. Textured boards and good drainage on stairs help on icy mornings.

King County sees about 37.8 inches of precipitation a year, with measurable rain or snow (0.1 inch or more) on about 95 days. Good drainage between boards, clean gaps and a ledger that is properly flashed keep that water from rotting the frame.

Summer heat is mild by comparison — average summer highs near 75°F and only about 2 days a year at 90°F or above — so board color can be chosen mostly on looks.

• Replacement and major repair: about 368,610 homes (37%) were built between 1970 and 1999, the age group whose original or early add-on decks are most likely to have worn-out framing, connectors and boards.
• Retrofit decks on older homes: about 338,412 homes (34%) predate 1970. Here the priority is confirming that add-on decks are properly attached — or rebuilding them freestanding — before any cosmetic work.
• Upgrades and expansions: about 163,527 homes (16%) were built since 2010. Their decks are usually sound but small or builder-grade, so enlarging the deck, adding stairs and switching to composite or upgraded railings are common.

50% of King County's homes are detached single-family houses and 5% are townhouses or other attached homes; 55% of occupied homes are owner-occupied. With mostly detached homes, wood remains a practical lower-cost option for homeowners willing to clean and seal on schedule.

Washington adopts building codes statewide through the State Building Code Council, with cities and counties enforcing them and issuing permits. Before work starts, confirm with the building department for your exact address whether a permit is required, what drawings and inspections it involves, and whether an HOA must approve the design.