Deck builders in Seattle, WA

Homes in Seattle have a median construction year of 1974, so a deck original to a typical house would now be about 52 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.

That makes Seattle's housing 9 years older than King County as a whole, where the median home was built in 1983. Statewide, the median Washington home was built in 1985. Among the 34 covered Washington communities with Census data, Seattle ranks #5 for oldest housing. In these ZIP codes, 37% of homes were built before 1960, 18% between 1960 and 1979, 16% between 1980 and 1999, and 29% since 2000 — the single largest group dates to the before 1940.

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 Seattle 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.

Seattle 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.

Budget, upkeep tolerance and sun exposure on your particular lot still decide the final choice between these options.

Seattle has about 497,219 housing units across its covered ZIP codes. 41% are single-family detached homes, 6% are attached homes such as townhouses and rowhouses, and about 53% are in buildings with two or more units. Roughly 47% of occupied homes are owner-occupied.

Because so much of the housing in Seattle is multi-unit, a meaningful number of decks and balconies are governed by condominium or building associations. For single-family homes and townhouses here, check whether any association rules apply before you design.

Because fewer than half of homes here are owner-occupied, rental property owners make up a share of deck decisions here; durable, low-maintenance materials often make sense for them.

• Retrofit decks on older homes: about 232,496 homes (47%) predate 1970. Here the priority is confirming that add-on decks are properly attached — or rebuilding them freestanding — before any cosmetic work.
• Replacement and major repair: about 118,132 homes (24%) 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.
• Upgrades and expansions: about 92,697 homes (19%) 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.

Seattle's milder winters — about 25 freezing nights a year — allow construction through most of the year. Spring and fall are still the busiest seasons, so booking early helps.

For Seattle, WA, ask the permit office whether your deck needs a permit based on its size, height and attachment to the house, which drawings and inspections are required. Statewide code background for Washington is on our state page; local rules change, so the building department remains the authority.

The closest covered area is Medina, about 4.3 miles from the center of Seattle's covered ZIPs. Its median home was built in 1973, 1 years earlier than in Seattle. Seattle has 58 percentage points fewer detached single-family homes (41% vs. 99%), which changes how many projects are backyard decks versus compact townhouse decks. Owner-occupancy is 47% in Seattle compared with 80% in Medina. Seattle's covered ZIP codes span about 143.6 square miles of land with roughly 497,219 homes — about 3,463 per square mile, dense enough that lot size, access for materials and neighbors' sightlines shape most deck plans.