Monday, November 24, 2008

Bamboo dome - "Romanchiku"

This weekend, the weather was superb - warm and sunny. On Saturday and Sunday, I went to Mugen Mura to help build a bamboo dome. There's already a bamboo dome at Mugen Mura that we built last year. It's the yurt-like thing pictured below. Wrapped in several layers of blue tarp and greenhouse plastic, it's warm in winter and provides good shade in summer.

First we cut several large bamboo poles in the forest above the compound. It's always impressive the way that living bamboo can turned into a building material in a matter of a few minutes.

This time, the dome is being built according to a simplified design. On Sunday, Boy Scouts, most of whom were actually Girl Guides to my way of thinking, were to construct the actual dome, using struts prepared in advance on Saturday. Nishizaki-san explains how the thing is to be built, based on blueprints and a pretty model.

Splitting the bamboo is the hardest part, requiring cooperation, coordination, and a high degree of trust in the hammer man. It all went very smoothly.

The joints inside the strips of bamboo have to be knocked off with a bill-hook, and the edges shaved off if possible for safe handling (we couldn't be bothered, and wore gloves instead).

On Sunday, the Scouts/Guides arrived and we started putting the dome together. This always involves a lot of headscratching and bewilderment, and general tying and untying of string. Those who tend to maintain opinions as a matter of course often like to voice them at this point.

When we reckon everything is in place, there's a concerted heave-ho, and the dome is raised into place. A lot of adjustment is then required to get a smooth and nicely rounded frame.

This time, it was a bit of a fiasco really. The new design, while perfectly good in itself, hadn't quite crystallized fully in Nishizaki-san's mind, and so there was uncertainty about how many struts should meet in one place. In making adjustments, the dome became increasingly wonky, and several of the ties in the struts came loose. Eventually we gave up. Since the dome would have been taken down immediately anyway, this didn't seem like a great shame.

With quiet determination, Nishizaki-san held his own 'hansei' (review) session, splitting some of the struts in half and making a 1:10 scale version to test the design. It worked.

On Saturday, as we sat in last year's dome eating delicious ton-jiru and zenzai, one of our number happened to mention that buying a greenhouse of similar size would cost a small fortune. This is surely something to reflect on, and not only for agricultural purposes. For emergency shelter, the full size thing or a 1:10 version would be easy to make, durable, and cheap.

On the way home, I spotted a howaito kyatto on a shurain. I thought it would make a neat photo, but it's just a skinny cat lying about on an undistinguished religious shed.


stew said...

Hello there Rodster

The BBC programme "Its Not Easy Being Green" showed a timber-framed geodesic dome greenhouse last week. They are about to go on sale in the UK at two thousand pounds for a 4.8m diameter model. That's pretty big, but the glazing looks like simple poly-tunnel poly, making the thing very expensive for what you get. If you wanted to build a smaller one and go solid glazing for better heat retention, you'd also have the problem of a lot of waste, since glass and perspex aren't sold in triangles. The same goes for standard building materials like plywood in dome houses.

Anyway the website is

I've got a 6 foot * 8 foot standard aluminium greenhouse frame I was given a few years ago, but have never set it up. I did check to see if any of the glass from the old house would fit, but all the panes were too narrow.

Keep us posted with your shed. That bamboo base looks great.

Rod said...

Hello Stew

Thanks for the info and link.

Before I start thinking about greenhouses, I'm going to have to try poly-tunnels first.

The Mugen Mura folks actually made a geodesic dome which is still sitting around dismantled in a shed.
It was a hassle to make, and it would be even more of a hassle to make something useful with as you point out.

The bamboo base may look great, but it's the cause of some anxiety. Cut bamboo only lasts for about 3 or 4 years, after which some shoring up will be required. How this goes is anybody's guess, since the shed on the base is now a very heavy thing...