Permaculturing in Portugal

One family's attempts to live in a more planet-friendly way

Geodesic dome chicken tractor

The next stage in the construction of our suite of deluxe chicken accommodation is to provide them with some outdoor space. The chickens have arrived, but they’re not ready yet for free-ranging as it will take them a little while to get imprinted on coop = ‘home’.

Hens

Our hens! The two in the background are crossbreeds between Cochins and the local Portuguese pesco├žo pelado or bare-necked hens. The two in the foreground are Green legs.

While they’re getting to know their coop, we’ve made a start on both a permanent pen surrounding the coop and on ‘tractor’ accommodation for putting them to work round the quinta.

I’ve been studying many chicken tractor designs over the last while, looking for something that’s light enough for single-handed moving, but is still large enough to provide the chickens with enough scratching and foraging space that it won’t require re-siting every couple of days. Since they have a permanent coop, the design doesn’t need to incorporate secure night-time accommodation. I kept coming back to the idea of a geodesic dome, encouraged by the success Milkwood Farm in Australia has had using this idea.

But once I started studying the detailed construction plans of their dome, I started to lose enthusiasm. The measuring looked complex and the black pipe I was planning to use doesn’t lend itself to being clearly marked, let alone colour-coded. When I got to ‘special blue solvent glue’ I ground to a halt entirely, having never seen the like in the local hardware stores. So it seemed to me that the traditional Buckminster Fuller-design 2-frequency (2V) geodesic dome was a lot simpler and easier to construct.

I inherited a fair amount of half inch irrigation pipe (16mm LDPE dripline) with this quinta, none of it actively in use at the time or since, a lot of it in fairly short sections, and some of it slashed by passing brushcutters where it had been hidden and half buried in undergrowth. Constructing a geodesic dome out of the shorter and damaged lengths seemed an ideal use for what might otherwise sit around gathering dust until I found another use for it. I wasn’t sure though whether it would be rigid enough to make a successful dome framework, so along with the nuts and bolts and chicken wire covering I needed, I bought some heavy-duty galvanised steel wire for reinforcement. (This, in any case, is needed to replace the vine trellises.) To begin with though, I decided to see whether the pipe on its own was up to the job.

Damaged 16mm LDPE dripline irrigation pipe about to be repurposed

Damaged 16mm LDPE dripline irrigation pipe about to be repurposed

The structure I decided on is a 2V geodesic dome. Thanks to one of several online geodesic dome calculators, it’s very simple to work out exactly what materials are needed for any given radius of dome, what lengths to cut the struts to, and how to assemble the framework once the struts are made.

I based the structure on dimensions for a 1.8m radius dome, but shortened each strut by 1.5cm at each end to allow for flattening and drilling the irrigation pipe to bolt it together, effectively reducing the radius to 1.7m. The dome is assembled as 6 pentagons, 5 for the circumference and one for the top, then joined together as shown in this series of images.

Softening pipe ends in hot water

Softening pipe ends in hot water

Crimping softened pipe with pliers. A mark on the pliers ensured each crimp was the same size

Crimping softened pipe with pliers. A mark on the pliers ensured each crimp was the same size

Drilling crimped pipe end. At last a practical use for the large gaps between the yurt floorboards (caused by shrinkage of green timber)!

Drilling crimped pipe end. At last a practical use for the large gaps between the yurt floorboards (caused by shrinkage of green timber)!

The centre of a pentagon unit bolted together

The centre of a pentagon unit bolted together

Ground level joints each have 4 struts apiece

Ground level joints each have 4 struts apiece

Interpentagon joints comprise 6 struts

Interpentagon joints comprise 6 struts

The first 3 pentagons joined. Will there be enough rigidity? Looking doubtful ...

The first 3 pentagons joined. Will there be enough rigidity? Looking doubtful …

The circle completed. A lot more rigidity as a result, though it remains to be seen how it will stand up with the top pentagon bolted on

The circle completed. A lot more rigidity as a result, though it remains to be seen how it will stand up with the top pentagon bolted on

Umm ... no!

Umm … no! Funky, but of no practical use.

Plan B. Insert 2 strands of galvanised wire per strut for additional strength

Plan B. Insert 2 strands of galvanised wire per strut for additional strength

Completed dome

Completed dome

But this was as good as it got. As soon as I tried to move it, the whole thing collapsed on itself again. Not only did the galvanised wire not help, but it made the situation worse as once the struts bent over, the wire (which had bent with them) tended to keep them that way.

There was, however, a big bonus from this stunning failure to accurately estimate the limitations of my construction materials. Seeing the completed 3.4m diameter dome immediately made me realise that a framework of this size (constructed from more robust materials, obviously) could be a very useful and versatile resource: covered in polyethylene sheeting, a Spring greenhouse; covered in fabric and canvas, summer visitor accommodation …

But back to the drawing board … I looked at the Robert Freeman design on Milkwood’s blog again and gave it some more serious consideration, but somehow I didn’t feel ready to give up on the original geodesic dome just yet. The dome I’d started with was pretty large. Too large. Not only for the frame it was made from, but for ease of moving and potential siting too. I decided to try a cut down version and reduced it to 60% of its original size, minus the galvanised wire. I also noticed that it was better if I didn’t do the nuts and bolts up so tightly – a partially deformed tube has more rigidity than a completely flattened one.

Geodesic chicken dome Mark II

Geodesic chicken dome Mark II

Night and day! This worked a treat. The resulting structure has integrity. It can be lifted with one hand, is flexible enough to be squeezed through tight spaces, but immediately regains its shape. It will need re-siting more frequently, but it will go anywhere on the quinta.

Geodesic chicken dome showing open door

Dome with wire attached and door open

The rim can be pegged down for security and there is a 40cm skirt of chicken wire beyond the perimeter which can be weighed down with rocks or planks to deter diggers – whether hens from the inside or other animals from the outside. The door is sited above ground level and it’s easy enough for a me-sized person to climb in.

Next stage is to see whether the chickens take well to it …

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10 Comments

  1. ali birch February 16, 2012

    Oh my goodness you must have the patience of a saint to keep on at that. Well done though it looks fab. I loved the slightly puzzled looking canine observer in the background!

  2. rick February 16, 2012

    wow, was about to message you about your chickens to see if they had arrived…….amazing dome thing wendy, very impressed with your patience, me, I have none, would love one as a greenhouse

  3. Laura February 27, 2012

    That’s so cool, lucky ladies! I’m very impressed. We’re just making a tractor too, it needs to be oblong for our raised beds but I’m completely inspired to use your technique for other structures!

  4. veronica March 29, 2014

    Hi
    I’m thinking of making something like this and I wonder if you know if it works on steep hills? Our little farm is all hill. We live in Alentejo. Always interested in other pioneers in Portugal!
    Best wishes
    Veronica

  5. Quinta do Vale March 30, 2014

    Hi Veronica. The steepness of the ground isn’t as critical as how even it is! You don’t want an uneven base for the dome because potential predators can get under the edges and chooks get out. Having said that, one of our chooks has a congenitally deformed foot and finds slopes quite hard to deal with … which is a bit unfortunate since the ground here is all sloping like yours. Basically, so long as the chickens are happy on a slope, then this dome will work fine. If you use tent pegs to peg it down, it should be very secure.

  6. Anthony December 10, 2014

    Excellent write up. I followed this process using 13mm irrigation pipe sold in Mitre 10 (NZ). It failed spectacularly, looking like your first effort despite having a radius of 1.7m. So just a warning for anyone else in NZ thinking of using this cheap pipe – don’t!

  7. Gypse February 23, 2015

    Awesome dome.

    I plan on making a geodesic chicken tractor in a few years time.
    I made a one tenth scale model out of 4mm irrigation tube.
    It worked spectacularly well.
    Despite the floopyness of the tubing the dome has amazing rigidity.

    My model is used as a cover over a pot to prevent insect attack.
    It is a 43cm diameter V4 7/12th dome. The longest struts are 71mm.
    Irrigation tubing is cheap but floppy. Even floppier when in the sun.
    It has a natural curve which is wonderful and is easy to join.

    Some thinks I learned…
    I used stainless steel pop rivets with washers.
    It’s difficult to compress the tube to get the rivet started.
    Most joins are 6way but if you use continuous tube, you are only joining 3 tubes at each join.
    I cut the tubes in half for the 5way joins (and did those last).
    The trick is to make the struts short enough to be rigid.

    According to the numbers you posted, your good dome is 2m diamerer so the biggest struts must be about 64cm. If this works with 16mm tube, I guess I need to go shorter with 13mm tube.

    A V4 half dome with a 160cm radius would have a max strut length of 52cm but you’ll need 120m of tube and 91 hubs.

    If I can’t get the irrigation tube to work I’ll use bamboo garden stakes.
    They are cheap, light, and stiff.
    The irrigation tube can still get used for the hubs.

    I also love your door.

  8. Quinta do Vale February 23, 2015

    Great tips! Especially using continuous tube as that would add a lot more structural rigidity. Even if it were just for the circumference at ground level and a couple of arcs through the 6-way joints. I’ve been thinking about building a bigger dome out of MDPE water supply pipe and casting melted-down aluminium cans into push-fit joining pieces, but that’s an awful lot of cans to melt down … There could potentially be a way to cut the pipe at the 6-way joins so it all just slots together neatly and then weld it with a blow torch into a firm joint. Still on the drawing board in my head at the moment but so much potential!

  9. Dana Martin November 10, 2015

    If you are prepared to go to the trouble making what you did, then you might have a look we have done with chicken domes. Our domes have been in use for years without trouble, very successful indeed!
    Full details at http://dmkpermaculture.com/how-to-build-a-chook-domechicken-domechicken-tractor/
    Good to hear permaculture is strong in Portugal, good on you.

  10. Quinta do Vale November 10, 2015 — Post author

    Nice structure! Thanks for posting the link. I made mine the way I did because I particularly wanted to experiment with a geodesic dome (thinking next step greenhouse … summer accommodation …) but this looks like it would do a great job as a chicken tractor.

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