Specification, Installation & Maintenance
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Receiving and Installation Guidelines and Protocol
The customer is responsible for receiving and proper installation of our products by following our guidelines, local building codes, and generally accepted construction practices.
Installation is the most important factor in exterior siding longevity for yakisugi “shou sugi ban” as for any exterior wood product. Please reference our General Siding Installation, Layout, Furring and Fastener Guidelines document for a thorough review of standard wood siding and paneling installation spec.
Offload and Break Down the Crate(s)
We crate each shipment as standard to prevent shipping damage, and ship by common carrier box truck unless the order is large enough for a flatbed.
Our standard terms are Incoterms Ex Works Portland Oregon and note that we arrange freight as a service for you, but are not responsible for trucking company service inadequacies. At shipment we will send the Consignee a Bill of Lading (generally with tracking) and ETA at site, but once the shipment leaves our shop, we are at the mercy of the trucking company and the customer is responsible for final delivery & offload logistics.
the crates are 150″ long and not designed for a pallet jack, so they cannot be lowered to the ground at site with the lift gate alone. Lumber is very heavy and if a forklift is not available at the delivery location, offloading may be difficult or impossible. In that case will-call pickup at the local hub, or delivery to the contractor’s shop, a local lumberyard, or logistics warehouse may be the best option. Please consult with us to minimize any hardship in delivery as some jobsites can be challenging.
If a dock is not available, offload to grade with a forklift by dragging the crate to the back of the box truck by strap or chain, then lower to the ground with the front end of the crate on the lift gate, back end of the crate on the forks. If a lift gate is not available, set the front end of the crate on the truck deck and the back end of the crate on a mocked-up A-frame (large sawhorse) at approximately 48″ height. then come around to the crate side with the forklift to pick up and remove. Or pull out with one forklift and come around the side with a second forklift to remove. We have a video to show how this is done, so please ask for us to send it to you as needed.
The crates are opened by first removing the Philips-head screws, T25 torx-head screws, or duplex nails holding the bottoms of the end walls to the pallet groover, then cutting the 4 steel straps with metal shears. Finally, one or two people on each end of the crate lift the entire lid/wall assembly in one piece straight up over the unit of wood. No need to break the crate down with a hammer and prybar unless the lumber has shifted dramatically or the crate was broken in transit. The wood is hand-bundled in 4- or 6-piece bundles for carrying easily around the job site, and each unit is factory-stickered every row for onsite acclimation without the need for scattering or re-stacking. If staged on a flat, level location, the units can be stacked up to 3 high to save space as needed.
Inspect the Shipment
Damage can occur during shipment, so always inspect the shipment before and during unloading and note any damage on the Bill of Lading, as well as with quality photos from different angles.
Inspect product specification and volume to confirm as correct. The planks are bundled face to face so make sure you are viewing the finished board face and not the backs of the boards during inspection. Contact us immediately if there are any issues.
Acclimate the Product to the Installation Location
Ensuring that the moisture content of the siding is at equilibrium before it is installed will minimize dimensional movement after installation.
We air and sun dry at the mill to 11~14% moisture content, and after warehousing and shipping, the wood is generally within this range. Each region has a different standard siding equilibrium moisture content range (generally 11~15% in regions with high precipitation, 6~12% in dryer regions), so the installer should confirm our wood scope is sufficiently acclimated before installation. If no moisture meter is used, we recommend acclimating yakisugi for two weeks at the jobsite before installation, ideally in nearby shade on an exterior application, or the project room at an interior installation. The longer wood is locally acclimated the less movement there will be after installation. A passable moisture meter only costs around $30 online and is a great investment if there is any question. To acclimate, store the siding out of direct sunlight, separate the bundles for air circulation, protect from direct moisture, and make sure the area is ventilated. Do not let the lumber get wet, but if it does then the hand-bundles must immediately be broken up and slip sheeting removed. We slip sheet with renewable and breathable paper, not plastic, and it can adhere to the freshly oiled planks if allowed to dry out stacked in place.
Finish & Touch-up
We recommend prefinishing before installation in order to coat the lapped male edge and for consistency.
99% of wood we ship is pre-finished with an oil stain at our shop before shipment. During installation cut surfaces such as cut ends, rips, drilled holes or notches should be coated with touch-up oil. Installer should have a can of finish and a brush next to their cut station to encourage this practice. To touch up oil stains, dab the oil on locally and then immediately and gently wipe off any residue on the prefinished face as drips or overapplication can blemish the factory prefinish, causing the spot to “flash”, or become glossy.
Nakamoto Forestry yakisugi “shou sugi ban”, just like all wood siding, must be installed on screen walls in exterior applications for good wood longevity and dimensional stability due to the use of modern vapor barriers.
Direct contact with the vapor barrier will cause any wood siding to rot, yakisugi included. We recommend 3/4″T solid-sawn softwood furring (also called “lathe”, “runners”, “purlins”, or “stripping”) over resin or engineered products. Minimum 3/8″ or 1/2″ thick air gap via furring suffices for many 1~2 story facades, and thicker than 3/4 is recommended when there is a layer of insulation between framing and siding. For screen walls, furring should be securely fastened to the sheathing or other substrate and be at a minimum of 16″ on center layout pitch (12″ pitch is recommended.) Two face nails per runner are necessary, and nailing should be close (3/4-1″) to the top and bottom edges of each plank to minimize cupping over time. We recommend a screen at the top and bottom of the walls.
Interior applications do not require furring and yakisugi can be used the same as any wood paneling. It is generally glued up with a tube type construction adhesive and pinned in pace while the adhesive dries.
Yakisugi can be installed vertically, horizontally, or diagonally. It is commonly installed as a cosmetic underlayment between rafter tails and roof deck in exposed roof eaves (beware of roofers using long fasteners.) If installing vertically start on the left side and overlap as you move towards the right. This is because all planks are milled with rootstock right and crown left, and it is good feng shui to have the planks oriented correctly. We believe this is critical for the owner’s good fortune. In our experience the soot layer and oil finish will erode faster if installed upside down. Square edge planks can be judged crown up or down by looking at the grain pattern (see this blog for more information)
We recommend using a sharp ultra-fine finishing carbide-tipped saw blade for cutting our products. The yakisugi cypress cuts, rips, and installs the same as standard wood siding, and our millwork produces extremely straight and consistent plank stock. Wear an OSHA-approved dust mask and eye protection when cutting and installing our products.
Yakisugi is traditionally 10mm / 3/8″ thick, but Nakamoto Forestry North America inventories a standard thickness of 15mm / 9/16″. 3/4″ is the most common wood siding thickness in North America, but thinner is actually necessary for yakisugi products due to the flash heat treatment. Burning a thick plank at high temperature causes too much moisture content variation between the surface and center of the planks, resulting in warping, crooking, etc., and heat treatment will not penetrate as well. 9/16″ is sufficiently thick to act as an exterior skin and to easily install with the same methods traditional for 3/4″. Yakisugi is very rarely burned on the back side, and only for fencing applications (we do not offer this option.)
Due to manufacturing process requirements we specialize in plank products and not profiles or other millwork used specifically as moulding, such as 4/4 or thicker trim stock. We offer matched surface S3S profiles 9/16″ thick, or moulding can be ripped from our standard plank profiles. Since this trim is the same thickness as the field, it can either be installed over the field or another detail solution implemented. Un-heat-treated wood is also often used as moulding with a stained finish to match the yakisugi, and siding can be butted to it or the trim rabbeted to receive the siding field. Outside corners can be mitered and pinned. We also offer extruded aluminum outside corner profiles as an accessory.
It is common in modern architecture to use folded or extruded metal profiles on corners or other transitions instead of a wooden trim detail. The field can be run to flashing and door and window penetrations. Flashing specifications are the same as standard wood plank siding. A 1/8″ or similar gap can be left open for breathing, or vertical gaps can be grouted with a color-matched high-grade urethane caulk. Never caulk horizontal gaps since they act as a weep.
Soot will be bonded into the prefinished surface, but the installers will get some soot on their hands and tools from the backsides and from cutting. After installation, wipe down the wall with a moist cloth or hose it down to remove any soot that made its way to the face via the installers’ hands during installation. For best color longevity either have us apply a second coat of oil stain during production, or better yet have your painting contractor apply a second coat of oil after installation. Even though the wood has increased longevity due to heat treatment, the color will still patina over time.
Finish Information and Surface Maintenance
Yakisugi “shou sugi ban” is a “maintenance-optional” exterior siding.
Exterior wood siding is mechanically degraded over time by UV radiation, atmospheric moisture and precipitation, freeze-thaw cycle, and wind. The owner chooses either to embrace the traditional “sabi” aesthetic and savor it as it develops into a rich patina over decades, or to simply re-oil at any time in the future to return color vibrancy. Suyaki will remain the same black color for decades before the soot layer wears off, and can be re-oiled periodically to keep it black even longer. Our Gendai and Pika-Pika products are heat treated the same as Suyaki and then brushed during production, and will weather in color the same as any kind of oiled wood siding. It is important to differentiate between wood longevity and color longevity.
Cryptomeria (“sugi” or Japanese cypress) is a rot-resistant wood species, and the heat treatment improves wood longevity by burning off the hemicellulose and turning the surface hydrophobic and case hardened. However, color change from weathering is the same as any wood siding. The rich patina that develops over time is valued in Japan. Traditionally, yakisugi was installed unfinished and left that way for the lifetime of the structure or until replacement. Historically, only higher-grade residences or public facilities have had oil stain finishes applied and maintained. However, Japan’s modern preference has migrated to oil prefinishes (the statistic is 80% of the market) due to availability and acceptance of finishes and desire to maintain color consistency for as long as possible.
For most customers, we recommend finishing our products with a high-grade oil stain, and most of what we ship has a factory-applied oil finish. When installed outdoors the extra UV protection will slow down the weathering process and bond in surface soot, and when installed indoors enhances the wood grain and makes cleaning easier. Note the typical weathering due to lack of finish or finish maintenance in photos in the historical gallery on our website’s “About Yakisugi” page. This is due to the lack of a repainting culture in Japan. Organic weathering is beautiful but many North American owners want the coor to stay the same over time.
Weathering speed and pattern depend on finish spec, pigment content, and method of application, the nature of each individual plank, local exposure to weather, and maintenance. Sun-exposed surfaces will gradually mellow burnt orange as the soot erodes over decades, moisture-exposed surfaces will gradually turn silver, and areas with protection from both will stay the original color. Finishing with a UV-resistant oil and regular refinishing per manufacturer instructions will slow down the aging process and allow the siding to retain the specified color longer. This will also allow the maximum lifetime possible by preventing dimensional movement, checking, and UV degradation of the fibers. Basically, yakisugi is similar to any other wood siding in terms of finishes. The main difference is that due to the product being sooty we are not able to use a standard siding roll-coating line and therefore cannot apply oil stain to all sides of the boards.
After initial installation and within several years depending on conditions, minute hairline cracks will open on the surface of exterior planks and the color will start to change. At this point the owner should decide whether to embrace the Japanese patina aesthetic and enjoy how the wood ages, or re-apply the oil stain in a maintenance program to keep the color fresh over time. Refinishing as soon as color begins to change will fill in these cracks and make a longer-wearing surface. Each maintenance coat of finish will generally last longer than previous coats did due to oil buildup. All exterior finishes we use are breathable for best thermal performance and longevity. Another important point on the finishes we specify is that oil stains erode gradually over time, different from paints that flake or peel.
Please consult with us for specific project requirements and our recommendation to match your spec.
All prefinishes will bond the soot to the surface and prevent it from coming off when touched. After installation the wall can be wiped down with a wet cloth or washed down with water, and there will not be a noticeable soot residue afterwards. Do not scrub unoiled Gendai since the color will change.
Natural unmodified plant-derived semi-transparent traditional oils (oxidizing monomers) will show the grain best but will need more regular maintenance to stay vibrant than modern semi-solid alkyd (polymerized) oils. This is because semi-solid alkyd oils have more pigmented UV-blocking surface residue that stays the original color until it erodes through, exposing the wood color. Wood finished with traditional oils will fade gradually over several years. Alkyds will have more consistent color for the first several years, then wood grain will show through after the pigmented surface residue erodes.
For maximum color longevity on exteriors we recommend alkyd oils with an unmodified oil component for lux appearance and elasticity. Alkyds are plant-derived oils (safflower, linseed, soy, etc) that have been chemically modified into a polymer and penetrate into the wood with a water carrier in solution. They offermaximum UV protection and erode gradually in a pixilated pattern instead of crazing and scaling off like paint. Alkyds have more defined pigment color.
For maximum depth of grain, natural color, and rich patina we recommend traditional oils containing both a drying oil binder and mineral oil carrier. Traditional oils have more organic, nuanced color.
For interior Suyaki applications petroleum- or plant-derived polyurethanes make a good-looking, washable surface.
For better wood longevity on exteriors, finish end cuts, rips, drilled holes, or notches during installation.
For best color longevity apply second or third coats of oil stain before or after installation.
Some professionals think that back-oiling wood will increase longevity or dimensional stability in exterior applications. There are mixed opinions on this and it is never done in Japan. We therefore only oil the back side by special order. There is no need to back-finish wood for interior applications.
Use a penetrating UV-resistant plant-derived finish for exterior. High pigment and trans-oxide load is the best UV-inhibitor available for maximum color longevity.
Cypress has premium longevity over most other species partially due to a fungi-resistant tannin content, but mainly since porous and quick-drying so that fungi are not encouraged to grow.
Tannins may leach from the cypress within the first year or so after exposure to atmospheric moisture, and stain lighter colored surfaces below. These stains will generally wash away with rain exposure within the second year after installation. This is normal for all cypress or cedar species. See the photos on our FAQ page. For this and other reasons, traditional Japanese design in most regions locates wood below stucco on elevations. If any tannin stains appear on the wood or lower surfaces and need to be removed, wash off with a mild oxalic acid product.
To keep siding color consistent over time, apply a maintenance coat of finish when the wood begins to change color. Generally, the first maintenance coat will be within 1~10 years for traditional oils, then additional maintenance coats will be needed further and further apart due to oil build-up. Alkyds normally last longer before maintenance is needed, and a general rule of thumb is a re-oiling schedule of 2~15 years. Or let it weather and appreciate the organic patina, also savor the lower cost and effort.
Before application of a maintenance coat, clean and prepare the surface as specified by the finish manufacturer. Wash with a soft brush or cloth, never with a stiff brush or power washer. A power washer will break open the wood’s microscopic cell walls and cause premature and inconsistent weathering. Never sand or scrape yakisugi.
A very weak TSP or soap solution, commercial no-wash neutral pH cleaner, or simply clean water, can be applied with a cloth and residue removed to clean off pollen, dirt, dust, etc. It is best to use a product supplied by the finish manufacturer if any cleaning agent is used before re-oiling.
• Always clean and refinish a hidden test area before attempting the entire wall surface.
Touch up of damage, such as scratches or dings, or local uneven weathering, can be done easily with the specified finish maintenance product. Traditional oils blend better than alkyds. Suyaki or Gendai damage can be touched up with a black or dark brown stain, or the original prefinish. A small nick can be carefully dabbed with stain, bleaching can be lightly blended with stain and a rag, or for interior even a magic marker or grease pencil can be used for quick cosmetic touch-up.
Scratches to our Suyaki with an interior urethane finish can be touched up with a waterborne polyurethane pigmented black with universal pigment. Damage or scratches to the Suyaki soot layer on exterior applications can be touched up by carefully dabbing black oil locally then wiping off any excess.
It is important to follow finish manufacturer’s instructions and to test when reapplying.