Make your own icosahedron greenhouse from these plans:
Ever since learning about Buckminster Fuller at art college I have been fascinated by icosahedral structures. Over a few years I have enjoyed the opportunity to experiment with some useful structures to make growing domes for food.
The first type I built, and the most basic shape, was the top of an icosahedron, a 20 faced sphere recognised even by the Ancient Greeks – it is one of the ‘Platonic Solids’. It is a form found in nature, for example some viruses have icosahedral shells.
Made from thirty hazel sticks gathered from the woods over a winter, and a length of polytunnel liner, the first growdome cost about £30, shown above. What I learned from this one was that growing spaces need a good airflow and that if you are going to strim around them, they need to be raised from the ground otherwise the strimmer will cut the lining. Also, one very important point – if you don’t anchor them down than they will simply blow away. This one lifted from the ground and flew for 30 feet, turning a complete somersault and landing the right way up, scattering all my seedlings over the ground. The dome was completely unharmed which gives you some idea as to the resilience of this structure.
Although my second geodesic growdome looks like a giant egg, it was a three frequency icosahedron, where each face is broken down to nine smaller trangles. I used bamboo rods and connected them with bits of old hosepipe nailed together into six-pointed star shapes. This had a good ventilation system, in fact so good that the blackbird family soon learnt how to get in and steal my strawberries, until I netted them out. The dome lasted for a couple of seasons and was made from recycled plastic sheets, bubble wrap and cling-film for less than £20, which was mainly the cost of the bamboo. The joints for this dome were too flexible and it gradually turned into an egg shape under its own weight. I shored the roof up for a season with a seven foot high ‘strawberry tower’, made of strawberry pots of diminishing size, stacked on each other. The problem with this structure was that it was just too complicated – such a small structure didn’t need so many rods and connectors. The great thing about this dome though, was that it was built on some old, concrete garage walls as the base which just worked so well for solar passive heat sink.
So, onto dome three. This is the top half a two-frequency icosahedron. I chose to go for a much stronger and permanent structure and ordered tannelised garden two-by-one especially for the purpose, along with sand and cement to put in a ‘crazy paving’ base from my garden of rocks (on the edge of Bodmin Moor). I can’t over-emphasise the importance of having a model to work to for dome building that has more than one strut length, otherwise it is easy to get lost in the structure. Marking the different struts helps too, I painted mine with some left-over wood treatment. I connected the struts using metal discs, pre-cut with shears and drilled using a cardboard template. These were made from a sheet of galvanized metal I found, and a sheet of corrugated galvanized roofing that seemed to have been flattened by a tractor.
Connecting the struts and raising the dome up on tyres allowed me to connect new pieces to the underside. I had to give special attention to the joints at the top because they took additional strain during the construction. I bolted plywood disks on for support. Piece by piece, it took shape and it became clear to me that a half-sphere dome would be easily tall enough rather than the five eighths dome I had intended to build. This was fine as it meant there was wood leftover for an inside structure.
I dug holes under each of the strut nexus points at the base and put in some uprights to clear the plastic lining sections from the ground and allow me to build-in ventilation. I cemented these uprights in – making horizontal corrections with a spirit level as I went round. I used a mixture of techniques to fill-in these undergaps: engineering bricks, concrete and dog-food tins, old slates, carpet, bricks and blocks with cement (one side was next to the gas output of our septic tank and I certainly didn’t want methane build-ups in the dome).
Then the floor went in, like a mini patio made from all the flattish rocks and bits of slate I could get my hands on. I painted some of the rocks at the back black, and left them raised to absorb more heat from the sun.
Finally, it was time to put on the polytunnel cover. I ordered another £30 worth because I intended to also recycle the cover from the original first dome into this one. This glazing part was quite laborious as I had to cut the sheeting into rough triangles, staple it onto the struts and then trim to size. It is best to work from the bottom up, then the rain will flow down, and not into, the dome due to the overlaps. Once I got to the top of the dome it got tricky and there was lots of stretching up a ladder. I had made one top triangle as a detachable window which helped with the top glazing and is essential for airflow. I also made a detachable window on one side for wheelbarrow access. All the overlaps were then sealed using a waterproof tape made for polytunnels. I made a door by taking out a cross strut and putting in hazel sticks which pushed the space open so as not to weaken the structure. This has a porch from which I hang netting to keep out the ever-present blackbirds.
The first season I had a good crop of blueberries, picking salad, coriander absolutely loved the warmth in there, squashes, tomatoes, basil and peppers. Since I have grown marrows, courgettes, tomatoes, cucamelons, stevia, more pepper varieties, melons, a lemon tree, avocados and more. I am in there every day tending my food and have even put in a sink and draining board with a water supply from rain water butts. The dome is now in its third year and the only maintenance it has required is a re-taping of the seams this year. All in all the wood, screws, plastic sheet, sand and cement cost me around £150, a great investment for a growdome which I hope should last five years at least.
Click the ebook cover above to find out more about the geodesic growdome.