The most useful thing to understand about siding is that it is not a waterproof layer. It is a rain screen that sheds most water, and the system behind it manages whatever gets through — which in Washington is always some.
What actually keeps water out
The weather-resistive barrier behind the cladding, and the flashing at every opening, penetration and transition.
That is where siding jobs succeed or fail. Beautifully installed cladding over poor flashing will let water into the wall, and you will not know until the damage is substantial. This is why the question to ask a siding contractor is about the barrier and flashing detail rather than about the product.
Western Washington: moisture
Persistent damp means walls stay wet longer than in drier climates, so drainage and drying capacity matter enormously.
Rain screen installation — providing a drainage gap between the cladding and the barrier so water can escape and the assembly can dry — is meaningfully better here than installing cladding tight against the wall. In our climate that gap does real work.
Material considerations: fibre cement performs well and is widely used. Vinyl is inexpensive and copes adequately. Natural wood needs maintained finish and will rot if neglected. Engineered wood products vary considerably, and the details of installation matter more with them than with fibre cement.
Eastern Washington: UV and freeze-thaw
Different failures entirely. Intense sustained sun degrades finishes and some materials far faster than anything moisture does in Seattle, so UV stability becomes the priority.
Freeze-thaw cycling works at every crack and joint over successive winters. Materials and installations that tolerate movement do better than rigid ones.
In the Tri-Cities and Yakima particularly, expect to renew finishes more often than a Western Washington homeowner would, and choose colours and products with that in mind.
Coastal exposure
Kitsap, coastal Pierce, Whatcom and the Skagit islands add salt air, which attacks fasteners, flashing and any exposed metal. Corrosion-resistant specification is a genuine requirement rather than an upgrade in those locations.
Wind-driven rain is the other coastal factor. On exposed sites, rain is pushed horizontally at the wall, which tests flashing far harder than it is tested inland.
What a siding project should include
Removal down to sheathing where the existing assembly is suspect, so what is behind can be seen. Inspection and repair of any damaged sheathing or framing. A properly lapped weather-resistive barrier. Correct flashing at every window, door, penetration and transition. A drainage plane where appropriate. Then the cladding.
Ask specifically what happens if rot is found once the old siding is off. In Western Washington that is a realistic possibility, and you want the rate agreed while the wall is still closed.
Sequencing with windows
If both are planned, do windows first or do them together. Installing windows after new siding means disturbing the new work and compromising the flashing integration that makes both perform.
This is one of the more common and expensive sequencing mistakes in Washington exterior work.
Choosing a contractor
Ask about the weather-resistive barrier and how they detail flashing at openings. A contractor who answers that specifically and confidently is a different proposition from one who redirects to product brochures.
The cladding is what you see. The detail behind it is what determines whether your walls stay dry for the next thirty years.