A Geodesic Dome Straw Shelter

For the last few weeks, I've been building the components for a 7 metre geodesic dome, which I will cover with tarp to make a shelter for my straw bales next year.

I have decided to make it with "Cundy poles". These are softwood poles, possibly forestry thinnings, that have had the bark removed by machine. The diameter is variable, and they are not absolutely straight, but they look strong, durable (they are generally used as stakes in the ground) and smooth enough to support a tarp without damaging it. They are also much cheaper than machine-round poles.

I've bought 80 poles of 2.4 metre length.

For each of my dome struts, I took a 2.4 metre pole and a couple of 20 cm steel straps, cut from longer sections of builder's strap.

Then I cut a slot in one end, 3mm wide (same as the strap) and 150mm long

Line up the strap on the pole with 3 holes projecting. Mark through 3 of the the other holes for drilling positions:

Keep the pole horizontal, keep the drill vertical

Drill out the pilot holes to 6.5mm

Five poles ready for assembly

The tricky bit: push, or quite often hammer, some 6mm coach bolts through the poles engaging the holes in the straps on the way. No problem, as long as those drill holes all went through parallel

The poles I used have variable diameter, so I had a selection of bolts: 75mm, 100mm, and 100mm all-threaded. Long ends like these ones got cut off with an angle grinder

Then, you do it all again on the other end of the pole. I'm using a jig here, a piece of 6x2 with two nails sticking though upwards, and they were 216 cm apart for the long struts, and 191 cm apart for the short ones. I've already cut the pole to length, and I'm marking up the drill holes on the second pole end to get the strut length  (measured between the outside holes in the steel) accurate.

I made 35 long poles, 30 short poles so this was quite a long job: 130 steel straps, slots, 390 bolts

 Construction, with a little help from my friends.

( I was hoping to have a time-lapse video here, but my camera wasn't up to it.)

So, in early November I had all the parts made and a 7 metre circle on the grass. I'm not going to give you the How-To-Put-It-Together instructions here, just show you some photos, maybe mention some of the issues that came up. It was a great thing to do as a team. I asked eight friends to help, expecting around half to come, but on the day I had seven; eight including me. And they were all needed! There was plenty to do.

We put 10 poles around the base, then joined them up. Next: - the Teeth. Five equilateral triangle constructed on alternate base struts. Each "tooth" is propped with a spare strut for now.

Keeping the props in place, we fill in the gaps until the first level is complete.

Scaffolding platform was essential for the next stages. We are completing the five base pentagons

These are around 3 metres high, and in the absence of any 3-metre props, they are supported for now by ropes on the outside.

Completing the second level. It was necessary to adjust the rope supports to line the joints up

Second level complete!

Happy man! Everything has come out dome-shaped.

Many thanks to Jim, Westie, Sandra, Malcolm, Toby, Andrew & Jess. Great fun, no accidents and a very sturdy-looking dome. Also to Moira, Jean and Chris for "support services" and photography

There was a gale forecast for the evening, so the original idea of getting the tarp on whilst everybody was here had to be scrapped.

Limecrete Slab

After many delays, the limecrete slab was laid by contractors The Limecrete Company on October 8th.

I had hoped that this would take place in late August or September. This would have allowed time this year, before the risk of frost, to build the stem walls. Because of the delay, I will have to build the stem walls in April next year, and will not be ready for wall-raising util the beginning of June at the earliest.

Preparation: approx. 250mm of recycled foamglass, Glapor brand from Ty Mawr, is laid onsite with a geotextile membrane below and then compacted with a plate compactor.

Recycled Foamglass: looks like a Crunchy bar, airy and very lightweight.

                                                                           

Delivery in bulk bags                                                

The Limectrete Company, Norfolk                     

Compacting                                             

250mm Average Depth                                       

Geotextile Membrane over Glapor           

 The Big Green Limecrete Machine                               

                Mixing 6 Cubic Metres in about half a day!              

Laying the slab                                                                 Floating                                          

And by the end of the day................................

And here it is a week later, now hard enough to walk on

The care advice for a limecrete slab is that it needs to harden for around 90 days before it can withstand frost, so I am going to have to do my best to protect it from winter conditions. Exposing it to air is helpful, and moisture is helpful at first.

October 24th. It's a warm and sunny day. In fact, it has been exceptionally mild since the slab was laid on October 8th, and no cold weather is on the forecast yet. However, it's November next week, and it's time to protect the new slab from frost. 

This is not exactly high-tech. I've spent £20 on tarpaulin, £15 on some bales of straw (not construction standard), and the method is best explained in pictures:

That took 3 hours, including trips up the road for straw and tarps. The idea is to leave the covers and the straw on the slab over the winter, and uncover it when I am ready to start building in the spring. It's dry and inviting under the tarps at present, hope it stays that way. There's a storm forecast for the weekend.

Guess what shape my temporary straw storage is going to be!

I hope my straw has been cut and baled by now. I am buying 120 bales from Longhay Ltd, who come recommended as construction-standard bale brokers. The plan is that it will stay in the farmer's barn over the winter and then be delivered here in May. At which point I will need dry storage in the garden for 20 cubic metres of straw.

You can buy a tarp garage to cover a small truck from Machine Mart for £360. Then there are Party Tents, available in a large range of sizes, and standard, heavy duty and extra heavy duty gauges. A 6 x 4 metre tent would be around £400, perhaps £650 for the heavy duty.

Then I saw this rather beautiful structure at a music festival, and thought: I could make one of these instead.

It's a 2V dome, very simple to make. What I like about this one is the way it's been covered with one large tarp and one small one. The large tarp has extra eyelets along one edge, and these are attached to struts along the opening. Then the whole sheet is pulled taught from the back and tucked under.

The dome pictured is around 4.5 metres diameter. I will make mine a little larger - perhaps 6.5 or 7 metres. This will mean that the "door" (as shown above) will be an equilateral triangle with 2.1 metre sides.

I thought about making it from hazel rods with water pipe strut endings, but had some anxieties on a number of fronts: would I be able to find a source of straight hazel rods, 2.1 metres long? Would any knobbly bits on the hazel rub holes in the tarp? Would it be strong enough?

I have decided to go with "Cundy poles". These are softwood poles, possibly forestry thinnings, that have had the bark removed my machine. The diameter is variable, and they are not absolutely straight, but they look strong, durable (they are generally used as stakes in the ground) and smooth enough to support a tarp without damaging it. They are also much cheaper than machine-round poles.

I've bought 80 poles of 2.4 metre length, now stacked up wigwam-style under a tree:

Straw Bale Workshop 2: Groundwork

This will become obvious quickly enough, so I shall tell you now: I am not a builder. I've made a few structures out of wood before, re-tiled a roof very badly, done some wiring, plumbing and small patches of plastering, but I'm about to embark on the first serious bricklaying I've ever attempted. 

First, I had to get the hole straight.  I had given my digger-driving neighbour some poor instructions, and needed several days with a spade and a wheelbarrow to get the hole to the right dimensions and depth. Here it is:

I hope that's deep enough. It's definitely subsoil, and straw bale buildings are relative light-weights.

Next job (according to the book, which is: Building with Straw Bales; A practical Guide for the UK and Ireland by Barbara Jones) is to lay a strip of limecrete around the edge 50mm thick and 150mm wide (2 x 6 inch). I did as much research as I could on materials and method, and this is what I came up with:

Buy 4 bags of NHL 5 from a conservation builder's merchant. Walk past the ballast at the regular builder's merchant, because I wasn't sure it was well-graded. (It looked like 20mm gravel mixed with sharp sand.) Luckily we have sand and gravel pits just down the road, so I bought half a ton direct from there. Hire a regular concrete mixer. Batches start with 1.5 buckets ballast, then 1 bucket lime, mix for a while, add another 1.5 buckets ballast, mix for 5 minutes, add enough water to make a dry mix (4 - 5 litres), mix for 10 minutes, then add another litre or 2 of water to make a sticky mix in a further 5 - 10 minutes. Wear dust mask and eye protection when there is dust around. Once the mix turned sticky, it needed a certain amount of poking with a piece of 2x2 to stop it from sticking to the mixer drum.

It's not a great photo-point of the project:

According to the photo data, this was on the 20th June. Limecrete takes a while longer than concrete to harden, so I started bricklaying in the second week of July.

The advice I was given was to use engineering bricks below ground, so I bought 600 very cheap, new ones. I have a pile of recycled bricks and local flint that I am planning to use above ground.

Mortar mix for this level was 3 buckets sharp sand to 1 bucket NHL3.5 with around 8 litres of water. The method was very similar to that for limecrete, i.e holding back the last couple of litres of water (and the stickiness) until the last few minutes of mixing. It's beautiful mortar to work with: no plasticizer needed, and nice and sticky for dressing the ends.

This section ends with a rather impressive-looking photo of my foundation with 5 courses of below-ground brickwork. Before we get there, I will just confess to some problems encountered along the way. The limecrete levels went wrong on the foundation strip, and I had to gradually get back to level by varying the mortar thickness. More seriously, I managed to get the brick bonds wrong, with 37 whole bricks along one side and 36.5 bricks opposite. Luckily, it's all below ground and no-one will ever see it. Unless you look closely at the photo below:

There are plenty of books and internet resources on how to do this right. This is more of guide to muddling through.

Here's the finished foundation:

It's not perfect, but I'm reasonable happy with it. More or less level, about the right size, reasonably square. It's July 12th 2013. My wall needs 4 weeks to harden, and I then have a contractor coming for the next stage: 250,mm recycled foamglass insulation and 150mm limecrete base.