Mercer Island Siding Replacement — Cedar to Hardie + Shou Sugi Ban Accent + R-5 Continuous Insulation

This Mercer Island home got the most thorough envelope rebuild we offer: failing cedar siding removed, new HydroGap WRB, 1-inch R-5 rigid foam continuous exterior insulation over the WRB, 1×4 furring strips creating a ventilated rainscreen cavity, and a thoughtful mix of cladding materials — HardiePlank lap, HardiePanel architectural panels in fine-sand texture, vented Hardie soffit, cedar soffit accents, and Shou Sugi Ban charred fir shiplap as the architectural accent. Custom-bent metal window trim throughout. New metal coping on every parapet finishes the assembly. As a Mercer Island siding contractor, this is the kind of envelope where every layer earns its place.

Why this Mercer Island project is different

Most Mercer Island re-sides we walk into are straight cedar-to-Hardie swaps — same wall assembly, just better cladding. This homeowner wanted more: continuous exterior insulation to break the thermal bridges through the studs, real wood character via Shou Sugi Ban accents without the maintenance penalty of regular cedar, and the long-term performance of a ventilated rainscreen cavity. The result is a wall that doesn’t just look better than what came off — it performs measurably better in every season.

The architectural detailing required four different cladding surfaces (Hardie lap, Hardie panel, cedar soffit, Shou Sugi Ban accent), custom window trim, plus the metal coping — which means every transition had to be planned ahead of WRB install. We walked the elevations against the architectural set before any tear-off began so the rough-opening flashing, the panel-to-lap reveals, and the Shou Sugi Ban accent boundaries were all set up correctly the first time.

The R-5 continuous exterior insulation layer

The single highest-impact decision on this Mercer Island project was the 1-inch R-5 rigid foam continuous insulation applied over the WRB before cladding. Most older Mercer Island homes have R-13 or R-19 batt insulation in the 2×4 or 2×6 stud cavities — but the studs themselves are only R-1 per inch of wood. That means about 25% of the wall area (the framing) is bridging heat directly through the wall.

Adding 1″ of R-5 rigid foam on the exterior breaks every one of those thermal bridges in one move. The functional R-value of the wall jumps significantly — not by R-5, but by closer to R-7 or R-8 effective because the framing bridge is now interrupted. On the comfort side: less drafty exterior walls, more even interior temperature, lower heating bills through Mercer Island winters. On the moisture side: the rigid foam keeps the structural sheathing warmer, which moves the dew point outward and reduces the risk of condensation inside the wall.

The 1×4 furring strip rainscreen

On top of the R-5 foam we installed 1×4 furring strips vertically, fastened through the foam into the framing. The 3/4″ cavity behind the cladding does two things: it creates the drainage path for any water that gets past the cladding (down and out the bottom of the wall), and it ventilates the back face of the cladding so it can dry. Both matter on Mercer Island where humid air sits against the wall for months at a time.

The 1×4 width is intentional — wider than minimum-spec furring (1×2 or 1×3) so the cladding fasteners have plenty of meat to grip. Critical when you’re fastening through 1″ of foam plus the furring before reaching the studs.

What we specified

• Tear-off of all cedar siding, plus removal of any failed substrate fasteners and inspection of the plywood sheathing. Patch where needed before any new layer.
• HydroGap® Drainable WRB across the entire substrate, shingle-style, sealed at every overlap. Why drainable WRB matters in PNW exposure →
• 1-inch R-5 rigid foam continuous insulation over the WRB, taped at all seams.
• 1×4 furring strips vertical, fastened through the foam into framing, vented top and bottom with insect mesh — the rainscreen cavity that lets the wall dry.
• HardiePlank® Lap (HZ10) on the primary elevations, fastened to the furring per Hardie’s certified-installer HZ10 spec.
• HardiePanel® architectural panels in fine-sand texture at the gable and feature areas — the fine-sand finish reads as a refined alternative to standard Hardie smooth or Cedarmill texture.
• Vented Hardie soffit at most eaves — non-combustible, lets the wall assembly dry at the top.
• Cedar soffit accents at architectural feature locations — back-primed, stainless fasteners, ventilated.
• Shou Sugi Ban — Charred Fir Shiplap as the architectural accent. The traditional Japanese yakisugi process: fir is surface-charred to create a layer of stable carbon that’s resistant to rot, insects, and weather. Reads as deep, tactile black at a distance with subtle texture up close.
• Custom-bent metal window trim at every window head, sill, and jamb — integrated with the WRB and the foam layer to keep water out of the assembly.
• Custom metal coping on every parapet — bent on-site, mechanically fastened, integrated with the WRB at the wall top. More on metal coping detail →

Custom metal window trim

When you add 1″ of foam plus 3/4″ of furring on top of the WRB, your window rough-opening detailing has to extend further out from the original framing — the cladding is now standing 1-3/4″ proud of the sheathing instead of sitting directly on the WRB. Stock window trim doesn’t fit that geometry. We field-measured every window and bent custom metal trim in the shop to wrap the rough opening, integrate cleanly with the WRB and foam, and finish flush against the cladding.

The cladding install

Once the foam, furring, and window trim were set up, the cladding install ran in clean sequence. Hardie lap on the primary elevations gives the home its architectural rhythm. HardiePanel architectural in fine-sand texture goes on the gable and feature areas. Cedar soffit accents at architectural feature eaves. Shou Sugi Ban shiplap as the focal accent. Each material chosen for what it does, not as a defualt builder default.

HardiePanel architectural fine-sand texture

The HardiePanel architectural panels in fine-sand texture are a step up from standard Hardie smooth or Cedarmill. The fine-sand finish has a subtle tactile quality up close that reads as architectural rather than mass-market. On modern and transitional Mercer Island homes the fine-sand finish pairs cleanly with white or light-tone field colors and against the contrast of Shou Sugi Ban accents.

Cedar soffit accents

Most of the eaves on this project got vented Hardie soffit — non-combustible and maintenance-free. At specific architectural feature locations we ran real cedar soffit instead, back-primed and stainless-fastened, with continuous ventilation behind it. The cedar reads warm and natural against the white Hardie field cladding, and pairs visually with the Shou Sugi Ban accents at the wall planes.

Shou Sugi Ban as architectural accent

Shou Sugi Ban (yakisugi) is one of the few real-wood claddings we install on Mercer Island that holds up to the climate without ongoing maintenance. The surface is charred to roughly 1/16″ depth, which creates a layer of carbonized wood that’s effectively impermeable to moisture, resistant to fungi and insects, and stable through freeze-thaw cycles. The traditional Japanese yakisugi process is 800+ years old — what changed on this Mercer Island project is sourcing it from a Pacific Northwest fir mill rather than imported Japanese cedar, which keeps the price reasonable while preserving all the performance characteristics.

For accent applications — entry surrounds, feature elevations, soffit panels, an accent strip across a gable — Shou Sugi Ban gives you the visual depth and tactile presence of natural wood without the 5–8 year repaint cycle of standard cedar. Pair it with the white or light-tone Hardie field cladding and the contrast reads as architecturally deliberate. More on premium wood siding for Seattle-area homes →

The install order

1. Walk every elevation against the architectural set before tear-off — identify cladding-material boundaries (Hardie lap vs panel vs Shou Sugi Ban accent) and any architectural details that need special flashing.
2. Remove all cedar siding plus failing fasteners. Inspect plywood sheathing — patch and re-fasten where needed before any new layer.
3. Install HydroGap drainable WRB shingle-style across the entire substrate, sealed at every overlap.
4. Re-flash every window and door rough opening — sill pan, head flashing with end dams, kickout flashings at every roof intersection.
5. Install 1″ R-5 rigid foam over the WRB. Tape every seam to maintain the air barrier and continuous insulation layer.
6. Install 1×4 vertical furring strips through the foam into framing, vented top and bottom with insect mesh. This is the rainscreen cavity.
7. Field-measure every window and bend custom metal window trim in the shop to fit the new wall thickness (foam + furring offset).
8. Install custom metal coping on every parapet, tied to the WRB at the wall top.
9. Install HardiePlank lap on the primary elevations, fastened through the furring per HZ10 spec.
10. Install HardiePanel architectural fine-sand panels in the gable and feature areas with sealed butt joints.
11. Install vented Hardie soffit at the eaves, with cedar soffit accents at architectural feature locations.
12. Install Shou Sugi Ban charred fir shiplap accent panels at the designated feature elevations — stainless fasteners, expansion gaps to spec.
13. Color-matched touch-up at fastener heads, caulk-and-tool at every transition, end-of-project magnet sweep for nails.

What this Mercer Island reside buys the homeowner

1. Measurably better thermal performance. The 1″ R-5 continuous insulation breaks every framing thermal bridge in the wall — effective wall R-value increases meaningfully, drafts disappear, heating bills drop. Most reside projects don’t add this layer because it adds cost and labor; this homeowner asked for it explicitly.
2. A 40-year envelope. HardiePlank in HZ10 has zero moisture absorption. Shou Sugi Ban accents need essentially no maintenance. The HydroGap WRB plus the 1×4 rainscreen cavity gives any incidental water a path to drain and dry. Metal coping on the parapets keeps the wall tops bone-dry. No part of this assembly is on a 5-year repair clock.
3. Architectural intent that reads from the curb. Hardie lap, HardiePanel fine-sand, cedar soffit, Shou Sugi Ban black accent, custom window trim, and metal coping — six different cladding/finish surfaces, each chosen for its specific role in the design. The home reads as a designed object, not a re-clad spec build.
4. One contractor, full envelope. Same crew did the tear-off, WRB, foam, rainscreen, all four cladding surfaces, soffit, parapet coping, custom window trim, and Shou Sugi Ban accents. No coordination gaps between trades.

The takeaway for a Mercer Island siding replacement

Mercer Island re-sides are an opportunity to do more than swap cedar for Hardie. If you’re already inside the wall — tearing off cladding, exposing the WRB — the marginal cost to add continuous exterior insulation, a real rainscreen cavity, and architectural variety in the cladding is small relative to what those upgrades buy you in performance and longevity. Hardie HZ10 with HardiePanel architectural panels handles the durability requirement, Shou Sugi Ban handles the “real wood character without maintenance” brief, and the engineered envelope behind it all is what makes the wall last.