Designing a roof made of a natural product, one that lasts more than just a couple of years, has been a challenge for me. Luckily, as sometimes happens in this amazing universe of ours, other people have obviously had the same challenge and suddenly there appeared on the internet and via friends, information on roofs made of bamboo tiles.
I had a good look all over the web, and friends sent me photos. I went to visit places with bamboo tiled roofs. Each roof had similarities and differences and eventually I came up with my own design.
One of my challenges was that I wanted to retain a dome-like shape. I already had a dome of bags of rice husks covered with cob and finished with a lime plaster. So my first step was to make the framework on which the bamboo tiles could be attached.
I cut down bamboo for the ribs and split it in half, as I wanted to have a gentle curve, and although I have tried different methods of bending whole pieces of bamboo, I have not found one that is appropriate for my needs. However, splitting bamboo in half works perfectly!
I also bought sheets/panels of already split bamboo. This kind of split opens up the whole piece of bamboo making it flat. These are available very reasonably priced in different sized panels. We cut these panels into lengths of 70 centimetres.
Then all the bamboo was put to soak in a borax solution for at least a week.
The bamboo frame needed to be attached at the top and the bottom of the dome somehow. There was no question of nailing the frame to the top as it was just bags of rice husks and cob. So we put a metal motorbike tire rim on a bed of old motorbike tires at the top of the dome. Long strips of bamboo were then attached to the rim with wire (lots of useful holes in the rim!).
I had already done a bit of planning for the roof, without knowing what it was going to be made of, when the building first went up, and had attached a wooden brace to the top of each of the 6 wooden posts of the building. However, I now realised this brace did not stick out enough, as I wanted there to be a gap between the limed roof and the bamboo tiles. So we added extra wood coming out from the top of the brace. Rebar was then bent to fit all around the dome and attached to the end of the braces, making a circular rim on which to attach the ends of the bamboo coming down from the top of the dome.
Our vertical bamboo ribs were about 70 centimetres apart when they were attached to the rebar. More ribs were then fixed horizontally covering the whole dome, 35 centimetres apart.
We bought an electric tool! It is the first one we have used on our buildings, but attaching hundreds of bamboo panels without a nail gun was not an option!
Each bamboo panel had a thin piece of bamboo at the top, and this was hooked over the horizontal rib and nailed on. Several nails went into the top part of the panel, which would not be a problem as it would be covered by the next panel on top. Thus, one 70 cm panel was overlapped 35 cm by the next panel creating a double layer of bamboo roof.
Right at the top we needed something to fit over the rather untidy junction of the bamboo ribs to make it look good and keep the rain water out.
Using bamboo and chicken wire we created a top-knot which was then covered in EPScrete, which is a fancy name for a concrete and styrofoam mix. This makes a very light-weight concrete, enabling us to build quite a large mini dome and still lift it up on to the domed roof by hand. A mosaic finished off the top-knot and a bell hanging from the centre gives a lovely sound in the wind. When we were creating the bell, it did not move enough in the wind, so I attached an old credit card to the bottom and now it moves very well!
Having a space between the cob dome and the bamboo tile will give the roof extra insulation, so I am expecting this to be a super cool roundhouse during the hot weather, and hopefully warm during our cold season too. Hot weather is coming up, so I will be trying that out first!
In the above picture you can see the gap between the bamboo tiles and the plastered roof – and a skylight made from an old car window that matches a similar hole in the dome to let light into the roundhouse.
Anyone out there trying this kind of roof, let me know if you need any more details, or just encouragement to experiment – I would be happy to help!