Decks are among the most attempted DIY structures and among the most consequential to get wrong, because they carry people at height.
The ledger connection
Where an attached deck fastens to the house. Deck collapses overwhelmingly involve this connection, which makes it the single most important part of the build.
Two things matter. The fastening must be structural — approved bolts or connectors rather than nails — and sized and spaced correctly for the load. And the flashing above it must direct water away from the wall rather than behind the board.
That second point is the Washington-specific one. Missing or poorly detailed ledger flashing lets water run behind the board, rotting both the ledger and the house framing it is bolted to. It happens invisibly over years, and it compromises the connection that everything depends on.
This is the strongest argument for permitted, inspected deck construction. An inspector looks at the ledger before it is covered, and nobody will see it again afterwards.
Permits
Generally required above a specified height above grade, and generally required where the deck is attached to the house. A low freestanding platform may fall below the threshold.
Thresholds are set locally, so confirm for your address. And remember which jurisdiction that is — city for incorporated areas, county only for unincorporated.
Eastern Washington: snow load and frost depth
This is where generic plans cause real problems.
Snow load. A deck in Spokane, Yakima or the Tri-Cities carries substantially more weight than a Puget Sound equivalent. That affects joist sizing, spacing, beam specification and post requirements. It is a structural design input, not a detail.
Frost depth. Footings must extend below the depth to which ground freezes, which is considerably deeper east of the Cascades. Inadequate footings get lifted by frost heave over successive winters, and a deck that has become uneven is usually telling you exactly that.
Online plans and kits typically assume milder conditions. If you are east of the Cascades, confirm the design is specified for your actual snow load and frost depth rather than assuming a general plan applies.
Western Washington: rot and drying
Persistent damp means decks here stay wet far longer, and the failure mode is decay.
Design matters for this. Gaps between boards allowing water to pass through rather than sit. Avoiding details where two pieces of timber meet and trap moisture between them. Protecting post tops and the joints where posts meet beams. Ensuring the substructure can dry.
Ground contact is where posts fail. Appropriate treated material and proper detailing at the base matter more here than in a dry climate.
Materials
Treated timber. Least expensive, needs finish maintenance, and treatment grade matters for ground contact.
Cedar. Regionally available, naturally rot-resistant, weathers to grey unless maintained.
Composite. Low maintenance and higher upfront cost. Copes well with Western Washington damp. Can get hot in direct sun, which is more relevant east of the Cascades.
Whatever the surface, the structure beneath is generally treated timber and is what determines the deck’s life.
Railings and stairs
Height, spacing and strength requirements apply, and they exist because falls from decks are a genuine injury source. Stair geometry — consistent rise and run — matters for the same reason.
These are inspected items, and they are also the parts most commonly wrong on unpermitted DIY decks.
Choosing a builder
Verify registration, bond and insurance. Ask specifically how they detail the ledger connection and its flashing, and east of the Cascades, what snow load and frost depth they are designing to.
Clear answers to those two questions tell you most of what you need to know.