A Japanese timber framed garden shed

[GRadice]

I like that idea, Ray. I'll play with it.

[GRadice]

Change of plans. A couple of friends who know Japanese architecture much better than I suggested a style that is nearly as simple but adds a few curves. I like these better, especially the second one. Time to get out the carving tools.

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[GRadice]

Shed's got wings, mostly. Three more rafters to go.

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[GRadice]

Barge boards are up. A friend came over today to help. Good thing because this really was a two person job. Trial fit, dismount it, some discrete joint surgery, and repeat until it fit. The first side took two and half hours working slowly with much head scratching and time up and down scaffolding. But we learned, and the second set took about 45 minutes. I'm happy with how it looks. Tight and solid with some gap not visible from below.



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[GRadice]

And rafters are up. Taped for coat of primer on the end grain.

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[GRadice]

One advantage of doing a small shed: I can cover the whole thing when it rains. This was our first real rain since early May. A nice all day drizzle. I was hoping to have the roof done by now but having the tarp takes some of the pressure off of finishing it.


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[GRadice]

I'm still working on the roof. It is slightly complicated. Sitting on the rafters are two perimeter frames. The lower one surrounds a set of ceiling boards and the upper one surrounds some plank decking. Furring strips sit on the ceiling boards and support the plank decking above. The upper frame is 15 mm wider than the lower frame all around to create a shadow line and also a drip line beyond the rafter ends. The frames are mitered at the corners and joined with a through and wedged tenon. There is a lapped joint at the ridge. And because I didn't have long enough stock to make the long arms of the frames of one piece I'm splice joining two shorter pieces. All of the joinery is slowing me down, but I'm having fun.

Here is a schematic of the roof structure minus any flashing. The surface cladding will be metal panels.

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And the splice joint I'm using for the long arms of the frames. The arms of the frame will be screwed to the rafters to keep the rafters in line and prevent them from sagging.

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[GRadice]

A bit more joinery. This is one of eight corner joints for the roof frames. The through tenon will be wedged. The arm on the left is Port Orford cedar (Chamaecyparis lawsonii) like the rest of the shed. But I ran out of POC of the proper dimension for the frame and substituted yellow cedar (Cupressus nootkatensis is the current name) which I could get locally, dry and ready to use. It is a good substitute: strong for its weight, easy to work, rot resistant. Both will age to a similar silver/gray and 10 years from now someone would have to look really close to tell them apart.

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[GRadice]

And the joinery for those perimeter frames where they meet at the ridge. The frames sit on, overlap a bit, and are screwed to the barge boards that I've already shown. According to the Japanese carpentry text I'm using as a guide the barge end frames have this odd joint which is not fixed by any wedges or pins but seems to mainly be used to align and register the frames on the two sides of the gable.

One thing I love about this text is that even though the text is in Japanese, which I can't read, the drawing are clear and measurements are proportional.

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And one set of my attempts.

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[r3nov8or]

Nice work.

I guess the old saying, "Japan wasn't built in a day, but it was built beautifully", rings true

[GRadice]

Nice work.

I guess the old saying, "Japan wasn't built in a day, but it was built beautifully", rings true

Good one. I'll remember that.


I recently watched a youtube video that said less than 1% of houses in Japan are now built with traditional methods like the ones I'm trying to use. Far too labor/labour intensive and therefore expensive. Having worked on my little project for over a year, I can see why.

[GRadice]

Floor joists are done. They have cogged lapped joints with the two sleepers. The joists were milled and then planed about 0.5 ml oversized and then I compressed them with a hammer. In Japan this technique is called kigoroshi, which means "wood killing." When humidity rises the wood swells and tightens the joint. Works better with softwoods like this than with hardwoods. Here is a short video.

kigoroshi 1 - YouTube


Then all are screwed down to prevent squeaking later.

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[GRadice]

Working on the ceiling boards. Ship lapped using a dado blade on the table saw. These are 138 mm wide and 16 mm thick with 9 mm laps. One side will be a show side and will be hand finish planed. Port Orford cedar as is most of the rest of the shed.

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Those boards were clear. Some of the others have either tight or empty knots. That can be fine for a shed, of course. But I realized when working the stock down to finished thickness that I could use the ~ 3mm bandsawn cutoffs from the clears and laminate them to the rough sides of the other boards. That took awhile (and a surprising amount of glue) than I expected but it worked. It will look nicer and the clear show surface will be easier to hand plane than one with knots, too.

Bad side:

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Laminated good side:

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On edge:
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Although in general one should veneer both sides of a substrate to avoid imbalances causing warping, in this case the main boards are only 138 mm wide, the wood is oriented in the same direction and is the same species, and will be screwed down and sandwiched between the rafters and furring strips every 300 mm. Fingers crossed that this experiment will be OK.

[GRadice]

I rabbeted and finished planed all the of the ceiling boards.

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I also finished milling some furring strips for the roof out of what we call Douglas fir. These will be cut to length when the roof goes on.
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And made a false ridge beam that will hidden but screwed down onto the visible ridge beam and support the roof deck planking.
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This piece was too long for me to make in one go in my shop so I spliced shorter pieces together in length and glued up in width. I've never seen this particular splice joint before but it seems to work. It was tricky to figure out since the whole piece is chevron shaped in cross section.

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[GRadice]

A friend came over this morning and together we got the subfloor pieced together and screwed down. The subfloor is 21 mm, 5 ply Douglas fir, tongue and grooved. And made right here in Oregon, about 130 km south of me. It is not rated for exterior exposure but I did spray it with borate salts to resist termites and fungi. I'm happy to report that it is solid, flat, and smooth. I was a little worried that those small section joists might be a little springy. But at 200 mm centers, robust perimeter beams, and well supported sleepers the whole system is truly stiff. The two of us looked like idiots jumping up and down on it but didn't move it a bit.

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Flushed with our success and encouraged by the weather forecast of no rain this week, we took the tarp off and started installing the lower perimeter roof frame, called a hirogomai in Japanese. The hirogomai has three functions. One is to keep the rafter ends from sagging and keep them a straight line. The second is to overlap provide a drip edge to keep the rain off the barge boards, and the third is to frame and hide the edges of the ceiling boards that sit on the rafters. I described how I chose to make the hirogomai somewhere previously.

Here you can see the front of the shed with the hirogomai in place.

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The overlap reveal on the left gable end.

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And I described earlier the splice joint along the long eave end members. I wanted to lay it out so that the splce fell exactly over a rafter and left even reveals on the two ends and closed up tightly. I got very close.

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That was a good day. And after we finished and my friend left I checked the forecast one more time. Oh NO! 50% chance of rain in the morning! A mad scramble to get the tarp back on. Got it done just after dark.