A £30 DIY greenhouse

icosahedronEver since I learned about Buckminster Fuller at art college, I wanted to experiment with making human-scale geodesics. So, as part of a new project – a book on DIY greenhouses on a budget, I constructed a surprisingly large greenhouse using wild hazel wood and a purchase of £30 worth of Polytunnel sheet, (which is about $50 for my USA readers at time of writing). This article outlines the procedure for building the structure – without too much detail of course – because I want you to buy the book !

Regular icosahedron

regular icosahedron

The first type I wanted to build and the most basic shape was an icosahedron, a 20 faced sphere recognised even by the Ancient Greeks – it is one of the Platonic Solids (Tetrahedron, Cube, Octahedron, Dodecahedron, Icosahedron).

An icosahedron is a regular polyhedron with 20 identical equilateral triangular faces, 30 edges and 12 vertices. It is a form found in nature, for example some viruses have icosahedral shells.

Hazel layout ready for dome

Hazel layout ready for dome

Every day my springer spaniel, Freya, needs a walk so often when we went I out I would find and cut myself the longest length hazel rods of a useable diameter I could find, (in addition to providing numerous sticks for the dog).

Over the course of a couple of months of winter I built my collection of straight sticks up to the 30 I needed. I trimmed them down to a optimal length of 196cm and laid them out ready to construct the shape.

The icosahedron greenhouse body

The icosahedron greenhouse body

The size of your dome is going to vary a bit depending on how you connect the struts to each other. There are several tried and tested methods for this. In an icosahedron each vertex (the singular of vertices) joins five struts – a very complicated joint for joining wood to wood.So for this basic dome construction I used a very simple method of drilling holes and connecting the struts with wire and rope. In order to stop the ends of my hazel from splitting, I lined each hole with a bit of used copper pipe.

the icosahedron dome framework complete

the icosahedron dome framework complete

I moved the top to the centre of the cylinder and set it up in a tipi shape. I untied each top vertex, re-threading the rope in some instances to allow for ‘settling’ of the wild wood, then attached the top struts. I supported the roof with a large stick from underneath for the last two struts. Six more reef knots and the basic structure was complete. I included a central pole to add stability to the structure, slightly lifting the roof tightened the dome up. I took this photo of my ‘greenhouse’ and published it on Facebook where friends and family could take the micky out of me for building a greenhouse with no glass.

the covered framework

the covered framework

The covering for this dome arrived the next day. I had ordered 3 x 7.3x 1m Sunmaster Tunnel Covers, but it arrived all as one big sheet. I cut oversize equilateral triangle sections and nailed them with small, flat-head, roofing nails onto the framework, folding over the sheeting to produce a stronger edge. This is where the fresh-cut timber came into its own – as it was still sappy it took quite a lot of pounding without splitting at all.

The dome in my garden

The dome in my garden

Three (oversize) equilateral triangles ( ∆∆ ) fitted the width of sheet and allowed for anomalies created by the wild wood and the foldover onto the struts. I later tidied-up these edges with a staple gun.
Icosahedron greenhouse

This dome is now full of seedlings as I write. I suspect I may have to tie it down when it gets very windy but that should be easy enough. It is not quite as warm as a glasshouse but certainly performs well in passive warmth capture as all the seedlings are sprouting.

My next project is to build one of these with every large triangle subdivided by three (eg nine trianges in each) – a ‘three-frequency, five eighths, alternate icosahedron’ – which is more of a dome shape. You can find out more about this at my ‘greenhouse dome specific’ site at: make a greenhouse.co.uk

headergreenhouse

Leave a Reply

Your email address will not be published. Required fields are marked *