Rainscreen siding in Seattle: why PNW walls rot, and how to do it right
Seattle gets around 37 inches of rain a year, most of it in a slow, wind-driven drizzle that finds every gap. That's why the difference between a wall that lasts 40 years and one that rots in 8 isn't the siding you choose — it's whether there's a drainage gap behind it. This is the single most important building-science detail for any home in the Pacific Northwest, and most "budget" re-side jobs get it wrong.
Why PNW walls rot in the first place
Walls don't rot because they get wet — every wall gets wet. They rot because they stay wet. When siding is nailed tight against the building wrap with no air space, three things happen: wind-driven rain wicks behind the siding and has nowhere to drain; water vapor from inside the house condenses on the cool sheathing and can't dry; and any flashing failure at a window or deck dumps water into a wall that can't shed it. Trapped against the sheathing day after damp day, the wall feeds rot fungus that eats the OSB and framing from the outside in. The cruel part: it's invisible. By the time paint bubbles or a window sags, the damage behind the siding is often years old and expensive.
How a rainscreen fixes it
A rainscreen is almost embarrassingly simple: you leave a continuous air gap — usually 3/8" to 3/4" — between the finished siding and the water-resistive barrier. That gap does two jobs at once. Drainage: any bulk water that gets behind the siding falls straight down the cavity and out the bottom. Drying: air moving through the vented gap dries the wall from both sides, so it never stays wet long enough to rot. It's the wall equivalent of hanging laundry on a line instead of leaving it in a wet pile.
How a vented rainscreen wall is built
- Sound sheathing & a water-resistive barrier. Start with dry sheathing and a continuous WRB (building wrap or fluid-applied membrane), lapped shingle-style to shed water downward.
- Flash every opening & penetration. Integrate window, door, deck-ledger and pipe flashings into the WRB so any water that reaches the barrier is directed back out.
- Install the rainscreen gap. Fasten vertical furring strips or a drainage mat over the WRB to create the continuous air gap.
- Vent top and bottom. Leave screened vent openings at the bottom and top of the cavity so air moves and water drains out the bottom — bugs stay out.
- Hang the siding. Install the finished siding on the furring with corrosion-resistant fasteners and properly detailed trim.
Miss the flashing integration in step 2 and the whole system fails — a rainscreen is only as good as the details at its openings.
Which siding to choose
Here's the liberating truth: in a rainscreen, the material matters far less than the assembly. Fiber-cement, back-primed and gapped, is a workhorse here. Cedar and quality engineered wood look stunning and last when properly installed and maintained. Any of them, hung on a vented rainscreen with correct flashing, will dramatically outlast the same product caulked tight to the wall. Choose your siding for looks and budget; insist on the rainscreen for longevity.
What it costs in Seattle
| Scope | Typical Seattle cost |
|---|---|
| Partial re-side / single elevation | from $15,000 |
| Whole-house rainscreen re-side | $40,000 – $90,000+ |
| Re-side + rot repair + new windows | priced after wall is opened |
Prices in USD. Cost rises with house size, material, trim complexity and how much rot is found once old siding comes off. We price after inspecting the wall.
This is the same moisture detailing we apply on every decks, siding & exterior project and behind every kitchen and bath we build — see how it ties into our kitchen remodel guide. To find out what's behind your existing siding, request a free estimate.
Rainscreen siding — common questions
What is rainscreen siding?
A wall assembly with a deliberate air gap between the finished siding and the water-resistive barrier. The siding sheds most rain; water that gets behind it drains down the gap and the moving air dries the cavity. It's the modern standard for wet climates.
Why does siding rot in Seattle?
Because water gets trapped against the wall. Siding installed tight to the building wrap with no drainage gap can't shed wind-driven rain or condensation, so it stays wet and rots the sheathing and framing — often invisibly for years.
Which siding is best here?
Fiber-cement (back-primed and gapped) performs very well; cedar and engineered wood last when installed on a rainscreen with good flashing and maintenance. The assembly matters more than the material.
How much does it cost?
A proper rainscreen re-side commonly starts around $15,000 and rises with house size, material, rot repair found, and trim complexity. We price after inspecting the existing wall.