Bamboo cordwood: some considerations?

Hi all,

I am thinking of building some small outbuildings where I plan to live in Taiwan, and with bamboo and clay both plentiful, thought a cordwood construction might be an economical and aesthetically pleasing solution. Of course, bamboo is hollow, but it is strong, and the buildings are neither multi-story, nor will I be supporting any long spans or heavy roof loads. Solid timber, while available (say, 4-6" diameter cedar), isn't cheap. I do wonder about whether I should dry and/or treat the bamboo, though, and since it's an earthquake zone whether there are precautions I might take. I believe I have seen people pour a more rigid, cement-based collar as a sill for roof supports.  What would folks recommend as a top sill? We also have the potential for extreme winds, and I worry about the wind catching the edge of metal sheet roofing. Is it fantasy to think I could lay bamboo lattice above the metal roof as substructure for a green roof? That would surely hold the metal down, and would keep the structure cool for those 100º July days, but I am uncertain about the loading of, say, 12" walls.  

Thanks!

You might want to try this with a very small structure first -- perhaps a little chicken coop, or a dog house, or a small tool shed.  I'm not sure exactly how you plan to make this work.  Will you fill the hollow bamboo with clay?

I wonder if you might not be better off to use the light-weight building methods of Japan (I know they use timber frames, but using bamboo for framing material you could do something similar).  How do the local people build?

Kathleen

Thanks, Kathleen. Actually I would be using a cement-based mix in conventional proportions shown on YouTube cordwood videos. It would be troublesome to fill the bamboo cavities with clay; doing so might also weaken its inherent strength. Yes, it's my plan to start with smaller outbuildings to refine my skill, and because I'm unlikely to get bamboo pieces of uniform length (owing to the nodes), one side will inevitably be uneven.  Good for a toolshed or chicken coop, though maybe not for a house. Building with bamboo is not a local architectural model, though it has been used by indigenous people for millennia. I have seen beautiful architectural works in Thailand and Indonesia, but not so much in Taiwan. Though intriguing, it's quite technical, too. Timber frame--or any wood framing, for that matter--is not practiced in Taiwan much at all owing to the lack of a local forestry industry, because of the ravages of moisture, and because of population density.  

I'm visualising sections of bamboo cut into lengths of about 1ft and stacked to make a wall? Seems like bamboo is less than ideal for this. As you say, it is hollow and my experience with it is that it isn't that long lived if damp. The hollow nature of the stems makes me think it would likely trap pockets of water inside the structure and rot. Probably surmoutable, but I wouldn't want to invest a lot of time in a structure to have it break down in a few years.

If bamboo is available why not build with it vertically in long lengths? It is very strong in vertical compression. Make some kind of stone footing to lift them off the damp, and a decent roof, and you are sorted.

Some architectural styles take long lengths of bamboo, split them down the length multiple times, and roll the bamboo out flat. These sheets make good flat surfaces for walls etc...   and can be secured to a basic timber or heavy bamboo frame.

The flat wall portions are sections of bamboo, split along the length and fastened to the timber structure.

Thanks, Michael. The issue of whether bamboo might trap moisture is surely a crucial question to resolve, and should be known by indigenous builders. In Taiwan, my friends tell me that architectural bamboo must be of a particular species, and must be at least 3 yrs. old. My guess is that it should be dried first, and perhaps sealed on the outside.  (Though indigenous builders would not use a sealant.)  You're right about bamboo's vertical strength: I would need some good design advice, though. I live in Hong Kong now and marvel at 20floors of bamboo scaffolding held together only with 3' lengths of thin plastic cordage. Building a big bamboo structure would be a dream, but beyond my present skillset (or of anyone I know in Taiwan). I have seen and think I understand the technique of using woven bamboo splits in a wattle and daub application, which could be good for interior walls.

Bamboos grow very rapidly in length, but continue to build strength and density for a number of years - hence the need to be 3 years old or more. The same holds true for harvesting simple canes for use in the garden.

I think they are traditionally not sealed - the outer skin has a near waterproof waxy finish anyway, and traditional designs have a roof with a large overhang. The roof is the most important part of keeping the walls dry, and prevents all but the worst blows rain from hitting the walls. Hence I can't see a need for walls to be sealed against moisture in most applications.

Any resources you could pass along about roof structures would be most appreciated. I did notice that in some Japanese applications that bamboo is heated to a point where they "sweat" an oil, which is then wiped off. And yes, bottoms are seated on stone or cement to keep them away from moisture. Lots of details that are way beyond my experience at this point.

Cheers,

Craig

Harvest when the sap is down, november through feb here in japan, dry for a year until evenly tan coloured, discard any with discoloring as that'll be rot setting in.
Three year old growth is best as mentioned above.
I'd also recommend splitting it and using it as laths under an earthen plaster rather than the cordwood idea.
Take a look at this blog for inspiration:
http://holzhueter.blogspot.com/p/blog-page_27.html?m=1

Not sure how true it is but I was told that when bamboo is heated it has silca or something in it that forms a very rigid glass like structure that seals out moister and becomes very ridged for building strong post. Not sure if it’s true just what I was told my an old boss.

I’m thinking on inclosing the bamboo or cordwood inside the concrete using a form to pour the concrete wall. Say cut 12” lengths of wood or bamboo and pour a 14/16” wall. I’m thinking the hollow bamboo sealed inside the cement would be a plus for installation.. I plan on going experimenting building livestock shelters.