Building a Timber Frame Engawa in Osakikamijima Island

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.

These notches are where the rafters will sit once installed.

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).

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.

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.

And here is the completed cutout of the mortises.

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.

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.

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.

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.

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

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.