I spent this past April once again working with Somakosha and had the pleasure of taking part in the raising of a small timber frame house. This house was built in the traditional style that Somakosha specializes in, Ishibatate; floating post on stone construction. However a big difference this time was the wall structure which was composed of tongue and groove boards installed between the posts. This method of construction is call ita-kura (板倉), and essentially makes a finished wall as the building is put together.
One advantage of the ita-kura method, is that it makes for a really strong structure capable of resisting lateral forces from earthquakes and typhoon. As the posts are raised the tongue and groove boards are slid down from the top, riding in grooves cut in the sides of the post. Once the boards are installed beams can be installed on top of the posts closing off the whole framework and making for a really solid structure. It’s a lot like assembling architectural scale frame and panel doors.
This house was very modest in size, and with 7 carpenters on hand we put everything together in 5 days. To see a time-lapse of the construction check out the video below.
All in all things went together really well, and the finished structure looks amazing. An ita-kura house can be used as-is with the tongue and groove boards exposed, or an additional wall covering can be installed to protect the boards and add another layer of insulation. In this case the client is going to finish off the final details on his own, and I believe he plans to cover the tongue and groove boards with another layer of wood siding.
Below are a few more shots from during and after the raising.
Here you can see the front side of the house with the ita-kura panels, and openings for doors and windows.
We used pegged mortise and tenon joinery throughout the house. We usually carefully pound joinery together with large mallets, but occasionally we use ratchet straps to help pull things together. While the ratchet straps are in place we pound in pegs to secure each joint.
Here you can see part of the interior ita-kura construction. We used hand planed and oiled Japanese cherry for this interior wall.
Below is another shot of the interior. Here we used walnut for the ita-kura wall joining with a round hinoki column. The handplaned surfaces and contrast between walnut and hinoki is really amazing.
Here’s a shot of the airspace on the underside of the house. The open airspace helps to keep the house dry and prevents rot and mold from forming. From here you can also see more of the post on stone construction. Between each post and stone there is a block of very rot resistant chesnut. The chesnut blocks act as another layer of rot protection by further separating the posts from the stones.
On the final day of the raising, we had a small ceremony to commemorate the raising of the house. The master carpenter prepares the display below containing offerings of sake and rice, and fundamental carpentry tools. Then we all gathered to wish for the strength and longevity of the house and it’s inhabitants.
Well thanks for reading about another adventure from here in Japan. There will definitely be more so stay tuned.
Another masterful documentary on house building in Japan. The lack of nails and glue, with the wonderful wood finish makes for a very beautiful and long lasting structure. How can we compare cost for this structure with a similar one using modern, western technology?
Thanks Jon
Keith, NZ.
Thanks Keith,
That’s a good question, and a deep discussion. I can’t speak to the actual cost of this building in particular but a traditional structure like this tends to be a better value both for the customer and the world at large. It’s quite possible that a traditional timber frame will be more expensive than a “modern” stick frame house, but the likelihood is that it’s going to last considerably longer and be a better long term investment. Here in Japan “modern” stick frame homes are only expected to last 30 years, at which point they are demolished and a new one built in it’s place. It’s ridiculously wasteful and short-sighted. Not to mention the fact that “modern” buildings are full of materials that are in no way biodegradable or recyclable.
Hopefully little by little, more people will take interest in building in ways that are more sustainable and mindful.
Jon
This is amazing Jon. Love the design and beautiful wood and that you celebrate the work done and hope for a long life for the house.
This is such beautiful building. Love the sharp contours and the contrast between the beams and panels. I am new to woodworking and seem to have become obsessed with Japanese joinery – really impressive.
Thank you, glad you enjoy the house, and it’s design. Japanese joinery and woodworking is a deep field and there are some truly mesmerizing buildings and joineries out there. Hope you have fun!
Thanks for these pictures and video. Nicely done.
I’m building a (much) smaller Japanese timber framed garden shed and I’m curious about a few details of the ita-kura wall design. I’ve not seen that done before. About how thick are those wall boards? You alluded to this but the design seems to be more an interior wall than exterior wall. And was there any kind of flashing or sealant at the sill/dai to keep water from running under the bottom wall board? Or was water proofing going to be done by the second outer wall?
Hey Gary, The boards are 30 mm thick, or around 1 1/8″. The boards essentially formed and inner hidden wall, as the client decided to put another layer of paneling on both the interior and exterior. In this case the 30mm thick boards are essentially acting as an efficient and quick way to close in the walls, while also giving rigidity to the structure. Typical Japanese traditional housed would have plaster walls that take much more time to complete.
As for water sealing, we didn’t do any sealing ourselves but I believe the client may have once we completed the raising. The client chose to do a bit of the finishing touches themselves. I wasn’t the lead carpenter on this project so I’m not sure how or why certain decisions like that were made. But I can say that I’ve never seen flashing on the top edge of lower beams, nor any sort of slope cut, and I believe that carpenters here primarily rely on the eaves for water protection. Eaves often extend out almost a whole meter which does add a good amount of rain protection.
That said, ultimately in addition to the deep eaves, flashing and a slope on the exterior of the lower beams would probably be a good idea.
Good luck with your timber frame garden shed. It’d be interesting to hear if you apply any of the ita-kura house method.
Best,
Jon
Hello. I admire this work. I build with wood in Mexico. And we have very little information on wood joinery structural design. Do you think you could guide me through this?
Thanks for the comment. Wood joinery as a topic is really broad, and depending on what you’re making, houses, furniture, etc. the design and necessary joinery will be different. If you’re interested in Japanese joinery as it relates to carpentry a good place to start is the book “The Complete Japanese Joinery” by Hideo Sato. There is a ton of good information in that book that may help get you started.
Thanks for sharing. Beatiful building. Are those posts 5x5in?
They are 120 x 120 mm or about 4.75 x 4.75 in. So pretty close to 5×5.
I want. Can they send the kit of parts and the crew to Wyoming?
Love to learn more particularly about all the joinery and it’s uses that this master builder knows. Especially if he does window work.