hinoki hot tub construction details are beautiful in their minimal simplicity and traditional craftsman expertise.

  • tub details:

  • function + minimalism

    Within a hinoki bath tub we can find represented many concepts of the japanese way of seeing the world. Complex details, multiple functions, technological inventions, influential styles and even historical conflicts can be all present, in a perfect balance, in the apparently simple line of an invisible wood joint.
    in Japan wood CRAFT is synonimous of ART ->
    Japanese tub craftsman
    hot tub install

    frame & apron

    wood tub details

    1 - PLANK EDGE
    The 42mm thick hinoki slabs are joined in such a way that the more permeable head of the plank is completely protected.


    ofuro details

    For tubs wider than 800mm, it is necessary to strenghten the top with a 60mm thick frame (kamachi).

    Japanese tub details

    Traditionally a copper apron is applied on the bottom to protect the side of the bottom plank. It has 2 functions:

    • avoid water to penetrate the wood perpendicular to the grain
    • the copper oxyde has a fungicidal action.


    ofuro details

    4 - NO APRON
    For a lighter, more natural look we can treat the bottom plank head with natural oil by Kreidezeit. In modern bathrooms this area is not so severely exposed to rot like it used to be in ofuro of the past.

    hot tub install

    joints & brand

    soaking tub

    The 42mm thick hinoki slabs are joined in such a way (T-joint) that the more permeable head of the plank is completely protected. The "dabo" is a good choice for a softer, natural look.


    Japanese bath

    Technique typical of the Tokyo (Edo) area. Each plate covers a long stainless steel screw which solidly connects the front with the side planks.

    wood tub

    We cover the joints with a copper plate "kugikakushi", the original technique developed from the ship construction. The copper turns green aftertime.



    8 - IRON BRAND
    We apply a hot-iron seal with our brand logo. Usually we propose to place it on the long side, towards the top right corner.

    hot tub install

    tub cover & bench

    hot tub Japanese tub cover

    The traditional tub cover consists of thin separated planks of wood. This type is easy to store as the planks can be piled up. When the lid is used to prevent the water from cooling down (which is the normal use in Japan) planks tend to warp overtime. It is a common practice to use them upside-down alternatively to prevent the warping.


    hottub Japanese bath lid

    We can also propose a lid in 2 pieces with handles. (easier to use but takes more space when stored) This will be more costly.
    Design and propostions are arranged to have a nice balance with the tub. But first of all ask yourself: do I really need a tub cover?

    Japanese tub bench

    11 - BENCH
    If required, we can equip the tub with an internal bench. This is recommended only for tubs that are enough deep or enough long. The bench should be fixed otherwise it would float. It is not reccomendable to use removable planks/benches inside the tub as it would definately scrath the bottom and walls of the tub, besides originating rot on the edges of the sit.


    hot tub ofuro removable bench

    Overwhelmed by many requests, we can now propose a removable type bench. We have 2 wooden lateral guides and a thick plank as a seat. The plank has some play to allow for natural dilatation and shrinking of wood. 2 plugs with chains prevent the seat from floating...

    hot tub install

    drain details

    wood tub drain

    13 - DRAIN
    The standard solution is a rubber plug with chain. It might be not the slickest design but it is safe, standard and easy to use. We can supply 2 types of drain fitting (see here to the right) More stilish alternatives include stainless plugs button operated but this require coordination on site. You are welcome to find a better drain from a plumber near you. Remember that hinoki planks can be 33mm or 42mm thick.
    The drain can be directly connected to the plumbing or can discharge into the waterproof pan.


    ofuro drain fitting

    We can install the drain or if you feel uncomfortable to decide a location now, we can provide you the fitting and have you drill the hole on site. This allows for precise coordination with the site and last minute change of mind. Since the planks are made of solid wood, it will be an easy job for your carpenter. Location: consider that if you have the drain in the middle of the tub, there is no place to attach the chain to. Also, it might be easily stepped on when entering the tub.

    short soaking tub drain

    15 - SHORT TYPE
    Short type fitting ends with a brass nut. Discharge is uncostrained and is applied usually when there is a waterproof pan (under the tub) and then towards a floor drain. Please find here an enlarged detail of the fitting. See also a scale drawing here.

      long Japanese bath drain

    16 - LONG TYPE
    Long type ends in a female socket (50mm, thread 1 1/2") so you can connect it to the drain. This socket is not longer than the thickness of the batten, so it will not reach the floor, even if you do not connect it to the drain pipe. See a detailed photo here. See also a scale drawing.

    hot tub install

    spout details

    hottub ofuro wall spout

    This can be fixed to the wall of laid on the tub edge.The spout is easily inspectable for mainenance. The wood rim forms a kind of a dam in order to distribute water evenly in a thin layer from the wide spout. This detail is hidden inside the spout head. Plumbing is same as floor mounted type.


    hot-tub wood tub floor spout

    Basically you can feed the H&C water pipes (or premixed water) into the spout consisting of a wooden box with a "beek" sloping outwards. Plumbing will not be visible. Please be aware that this shape (column type) will be quite expensive.

    Japanese bath spout

    A wall mounted spout costs about 700~800 USD (both for hinoki and asnaro) You can find here some shapes for your reference (pdf download). If you send us a sketch, we can build a spout as per your custom request.


    Every situation is different, you should evaluate the following: 1) are you bringing in hot&cold or premiscelated water?
    2) you should reduce pressure so to avoid water sprinkling under the cover (and since it is not sealed, from leaking out)
    3) use 180degrees elbow to direct water away from the lid
    4) do you have also a line for recirculated water?
    5) you should open holes on site to match size and location of your piping

    check: reference diagram for spout plumbing

    hot tub install


    You should have at least 1/2" of clearance around the tub. This allows for seasonal shrinking and dilatation and facilitates the circulation of air between tub and wall.
    There are 3 solutions for this detail:
    1- leave the narrow gap open (traditional japanese way). Water flows between the wall and tub, keeping the outside face of the tub clean.
    2- seal the gap with caulking
    3- plug the gap with thin stripes of hinoki that are wedged inside (we can supply those free of charge).


    ofuro overflow

    22 - OVERFLOW
    When you enter a japanese tub, the water will overflow from the top in the 4 directions. If you want to direct the overlow in one direction only, we can apply this type of cut both for singl plank tubs or kamachi frame tubs. Another option for the overflow is to have a couple of drain fittings about 50mm o.c. below the border, connected to the drain. The disadvantage is you will hear the noise of water and air being skimmed and sucked. See also notes about waterproofing in the installation section

    wood tub bark waterproofing

    If you look closely, you will notice some buffer material between bottom and wall planks. This is hinoki bark which is used as a natural waterproofing/fungicidal material at the connection between bottom and wall planks.


    ofuro tub natural oil finish for soaking tub

    The hinoki wood is never uretan coated in order to allow the wood pores to breath and release aromatic oils. As an extra precaution, we may propose to finish the sides facing the walls (outside face only) or the bottom with a natural clear oil produced by the german company KREIDEZEIT. http://www.kreidezeit.de/

    hot tub install
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    hinoki hot tub construction details are beautiful in their minimal simplicity and traditional craftsman expertise.