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Building a Timber Frame Engawa in Osakikamijima Island

Japanese timber frame hip roof construction

One of the first projects that I worked on with Somakosha was installing flooring, doors and windows for a timber frame home that Somakosha built on a small Island near Hiroshima. A little over a year later, the client asked us to add an engawa around the whole building. An engawa (縁側) is similar to a covered porch or veranda. But compared to wide expansive porches that you sometimes see in western architecture, in Japan engawa are often a narrow space (around 1 meter wide). In this case we were adding the engawa to offer the main structure more rain and sun protection.

The client asked that we use natural logs from his property for the posts. Osakikamijima is quite far from the shop so we decided to cut the joinery for the posts on site. However we did cut all of the joinery for the beams beforehand in the shop. Below are the various beams that wrap around the building and support the new engawa roof structure. The large diagonal cuts in the end of a few of the beams are for hip rafter joinery.

engawa roof structure beams and joinery
口脇 kuchiwaki cutting the notches

These notches are where the rafters will sit once installed.

口脇 kuchiwaki notches for for rafters in beams

After completing the shop work, we loaded all the lumber pictured above onto a truck and took a ferry to the island.

Rural Island Japan Ferry
Rural Island Japan

As construction sites go, it really doesn’t get any better than this!

osakikamijima engawa addition scenery

The logs below are what we used for the posts. Much larger than what you would typically see in a traditional construction of this scale, but they were what the client had available, and in the end looked really nice. That said they were heavy! There were a few varieties of wood for the post including Japanese beech (シイノキ).

engawa natural logs laying out and cutting joinery

We spent a few days cutting all the post joinery. Joinery layout on round logs is something that I definitely want to do more of. It’s a detailed process but really rewarding when you cut the joints and all the pieces come together cleanly.

Below are our layout tools, a variety of sumitsubo (ink pots), string lines, levels, etc.

japanese timber frame layout tools
engawa post tenon layout
engawa post layout and cutting

The mortise layout on the post below is for the floor structure joinery. The majority of the posts had some sort of joinery like this for attaching the floor structure. It’s much easier to layout on a flat surface than a round surface, so we cut a flat area around the location of each mortise.

engawa post layout for nuki

And here is the completed cutout of the mortises.

engawa post nuki joinery
engawa first post completed

Below is the same style mortise that we cut into one of the existing posts of the main house. The floor structure tied into the existing structure with the same sort of joinery.

engawa nuki joinery

Here is a detail of the floor structure joinery. In Japanese this joint is called 片下げあり (kata-sage-ari), which I believe translates roughly to “one-sided drop down dovetail.” Essentially a tie-beam (nuki) with a half dovetail cut is inserted into the post and drops down onto a mating dovetail. A wedge prevents the tie-beam from ever pulling out. We also put a screw in each wedge to prevent the wedge from ever falling out.

Below you can see the front side of the house as little by little we set posts in place and began assembling the floor structure.

engawa posts and nuki assembly progress
engawa posts and nuki floor structure assembled
engawa floor structure assembly
engawa nuki to old structure joinery
engawa post to nuki joinery
post to nuki joinery and wedges

Once we set the posts in place and joined them with the floor tie-beams we began to install the beams for the new roof structure. These beams were close to 8 meters long (around 25-26′) which is too long to transport and difficult to handle, so we spliced two 4 meter beams together in the middle with a kanawa-tsugi joint.

engawa addition assembly posts and beams

Once the main roof support structure was in place we began to install the rafters. The notches that we cut into the beams really simplified the process of locating the rafters. After we set the rafters in place, we cut the ends to final length leaving a nice clean line.

engawa roof rafters

Below you can see one of the hip rafters and the roof decking boards on the front side of the building.

engawa roof rafters and boards

We wrapped up our work on the engawa once we nailed down all the roof decking, and afterwards the client hired a roofing crew to install a metal roof. The existing roof of the main house is a green roof, and you can see some of the plants growing up there in a few of the pictures.

The finished engawa has a rustic feel thanks to the big curvy posts. Overall, I think it blends really nicely with the green roof and the earthen plaster walls of the main house.

I personally find site work to be stressful at times. Site work can be chaotic; tools forgotten or missing; unforeseen problems always arise; and general workflow tends to get interrupted more. Site work in Japan also often involves being away from home for weeks on end which can be especially difficult for people with families. But it’s hard to complain when you work at a site like this. Aside from the fact that we were doing really interesting layout and joinery, the clients were incredibly kind and served us amazing food; we bathed in a wood fired tub next door; and the scenery was incredible. Sometimes carpenters in Japan get a break.

Thanks for visiting.

Japanese timber frame engawa construction complete
engawa addition complete
Japanese timber frame engawa
post and nuki joinery and floor boards
Japanese timber frame hip roof construction
Japanese timber frame engawa

「Building a Timber Frame Engawa in Osakikamijima Island」への8件のフィードバック

  1. Hi Jon
    I am so envious of the wonderful opportunities you have to learn and practice traditional Japanese wood skills. Thanks so much for telling your story
    Yes the island is beautiful but I went only as a short term tourist
    Again, thank you

    1. Thanks Keith,
      I’m glad you’re enjoying reading. Perhaps someday we’ll have an opportunity to meet here on the island!
      Best,
      Jon

  2. Hey Jon,
    Thank you so much for sharing these stories and photos. I am enjoying and learning a lot!
    I am wondering if the joints that have wedges inserted below the beam are also the half dovetail, just with the dovetail portion on top. This seems like it would get the wedge out of the way of the deck boards.
    Also, how did you conceal your fasteners that hold the decking?

    –Toby

    1. Hey Toby,
      Yeah the beams with the wedges inserted below are exactly as you thought, with the half-dovetail on the top. Like you said it keeps the wedge out of the way for the deck boards. As far as the deck boards are concerned, they were “toe-nailed”/screwed in from the side at an angle to conceal the screws. In some situations they were also toe-nailed from below.
      Thanks for the comment!

      -Jon

  3. Jonathan David Coode Morris

    What angle is the fall of the engawa roof? This will be essential as I plan to emulate…many thanks for your post. Johnny.

  4. Beautiful! Bit confused though. How do you install the tie beams in when the beam is longer than the space between the posts?

    1. In some cases the tie beams/nuki were slid into one side and then the opposing side’s post would be slid into place, sandwiching the tie beam. For the longest span on the front side of the building the tie beam is so long that it gets spliced, and you can see half of the piece with exposed splicing joint in one of the pictures above. The spliced part of the joint eventually became largely hidden and structurally supported inside a post that was later slid into place.

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