Greenwood Cedar-to-Lunawood Reside — Cross-Batten Rainscreen
The problem: cedar that never got a chance to dry
The homeowners called us six years after their previous siding project. They had 1×6 tongue-and-groove cedar installed directly over Tyvek — no rainscreen, no drainage cavity, nothing between the back of the board and the wrap. In Greenwood — wet Seattle winters, shaded north elevations, leaf litter trapped against the wall — cedar installed that way is a countdown timer.
Cedar needs to dry both ways. If water gets behind the board (and in Seattle it will — windblown rain, capillary suction at joints, humidity from the soil), the only path out is the same way it came in. Without an air gap behind the board, the wood stays saturated. Saturated wood cycles between wet and dry, cups, splits at the tongue, and eventually rots from the back side — which is what the homeowners were seeing.
This is one of our recent cedar siding installation Seattle projects — a real home in Greenwood where the previous installer skipped the details that keep cedar alive in the PNW. Cedar siding replacement in Seattle fails the same way on nearly every house we inspect: no rainscreen, no drainage plane, and a wrap that can’t dry the boards from behind. Here’s what the rebuild looks like when it’s done right.
What we specified
The homeowners wanted vertical cladding for the look, and they wanted it to actually last this time. Three decisions solved it:
- Lunawood instead of standard cedar. Lunawood is Scandinavian pine heat-treated at about 215°C in steam — the process drives out resins and changes the cell structure so the wood absorbs far less water, shrinks and swells less, and resists rot without chemical preservatives. It behaves more like a tropical hardwood than softwood cedar in the PNW.
- HydroGap as the weather-resistive barrier instead of standard Tyvek. HydroGap has molded 1mm spacers on the face that create a continuous drainage plane against the sheathing — so even if water gets past the rainscreen, it has a dedicated path downhill to daylight.
- Cross-batten rainscreen. This is the part most installers skip. When siding runs vertical, the first layer of battens has to run horizontal (so there’s something for the vertical boards to fasten into). But horizontal battens alone trap water at every board edge and block vertical airflow. So we installed a second layer of battens vertically on top of the first. That gives us a drained AND ventilated cavity behind the Lunawood.
On top of the wall assembly, we re-fabricated the metal coping on the parapet — custom-bent on site to match the wall’s slight out-of-square, hemmed drip edges top and bottom, and sealed seams. Parapets are where a lot of Seattle houses leak; flat tops catch water and dump it straight into the wall unless the coping sheds it clear of the cladding.
The install
We pulled the old cedar, inspected every square foot of sheathing, and replaced rotted panels before the wall went back together. HydroGap went on next — taped seams, integrated at every penetration, flashed into the window openings with a head-flashing detail that drains over (not behind) the WRB.
Then the horizontal battens — pressure-treated, furred over the studs, with weep gaps cut into each row so water that makes it into the cavity can still drain down the drainage plane. Vertical battens on top, aligned with studs so the Lunawood has something structural to fasten to. The cross hatch creates a continuous ventilated cavity behind the final cladding — air in at the bottom, out at the top soffit, drying the boards from the back side 24/7.
Boards were fastened with stainless — fasteners are the silent failure point on most wood cladding projects; anything less than stainless will leach and stain the wood in a few Seattle winters.
The takeaway for Seattle homes
If you’re looking at real wood cladding on a Seattle-area house, the wood species matters less than the wall assembly behind it. Western red cedar can last 40+ years in the PNW if it can dry. Lunawood, Accoya, or thermally-modified ash can do even better. The same boards installed directly over a wrap with no drainage plane and no rainscreen will fail in five to ten years — we see it constantly.
For vertical cladding specifically, the rainscreen has to be cross-battened. A single layer of horizontal battens gives you fastening and drainage but blocks vertical airflow behind the boards. Single-layer vertical battens give you airflow but nothing to fasten to and no horizontal drainage. You need both layers to do both jobs.
Frequently asked questions
What is Lunawood and how does it differ from cedar?
Lunawood is Scandinavian pine thermally modified at about 215°C in steam. The heat treatment drives out resins and changes the cell structure, so the wood absorbs far less water, moves less with humidity, and resists rot without chemical preservatives. Compared to Western red cedar it is more dimensionally stable, dramatically more rot-resistant, and weathers to an even silver-gray if left unfinished.
Why does vertical siding need a cross-batten rainscreen?
Vertical boards need vertical battens to fasten to structural framing. But a single vertical batten layer has no horizontal drainage path and no way to bridge the stud spacing. A cross-batten assembly — horizontal battens first for drainage, then vertical battens on top for fastening and airflow — gives the wall both continuous drainage AND continuous vertical ventilation behind the cladding.
How long will Lunawood last in the Seattle climate?
Installed to spec over a rainscreen cavity, Lunawood is rated for 30 years against rot in Service Class 3 (above-ground, exterior) exposure. In the PNW that typically means 30–50 years of service life as long as drying is preserved. Installed directly against a wrap with no rainscreen, any wood siding will fail prematurely regardless of species.
Do I need HydroGap, or is standard Tyvek enough?
Standard Tyvek is a water-resistive barrier but not a drainage plane. In a wet climate with wood or fiber-cement cladding, a drainage-plane WRB like HydroGap dramatically increases drying capacity by giving trapped moisture a dedicated path downhill. For wood cladding specifically, we spec a drainage WRB every time.
References & manufacturer resources
Planning a wood reside in Seattle?
If your cedar is failing or you want vertical Lunawood on your next project, we’ll tell you honestly whether your wall is ready — and what it takes to make the cladding last the second time.
Request a written assessment