Prototype

Today’s Pyrapod has developed from an original prototype begun in 2014.  This page is the story of how that first design was built…

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I began by levelling an area of ground 6m square. This took approximately a week of digging by hand.

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The timber is larch, sawn at a sawmill 10 miles from the Pyrapod site.

I began construction at the end of June 2014 and worked on it whenever I could in between paid work and being away volunteering at off-grid communities. To prove out the practicality of building with minimal dependence on fossil fuels I used only hand-tools (no power tools), the key ones being hand saws, a brace for driving screws (excellent – try it!), and hand-powered drills.

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By November I had got to this stage where, as you can see, I have a timber structure sitting on slabs. This timber is mostly 4 x 1-1/2 inch. Once all the frame was in place the structure became incredibly robust. The assembly of triangles means it doesn’t move at all, even when you push hard on it! This reassured me that the structural design was very good.

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In December I added a waterproof breathable membrane external to the frame, secured with battens. This is to keep the timber dry from rain whilst still allowing the wall to breath so that moisture does not get trapped inside it.

This is a significant and reluctant exception to the principle of only using renewable materials, but my reasoning is:

  • it is a responsible use of resources as it will keep the wood going for much longer
  • in a low-carbon future it could be substituted by another material such as waxed canvas, or something I haven’t thought of or discovered yet.

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By the spring of 2015 I had fitted the cladding onto the roof battens, and started doing the same on the walls. The cladding is lapped larch from the same sawmill which since June 2014 I had kept stored under cover to season.

Within the cladding on the south-facing roof I fitted a velux-style window, to give ambient light and also controllable ventilation.

By the end of August all the roofs and integral gutters were complete, walls clad, window-sills added, and the door made.

The double-glazed triangular window units were fitted in September, as well as one for the door.  The Pyrapod was now externally complete.

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In 2016 the 4-inch thick wool insulation was fitted in the walls and roofs. The major shift in focus though in 2016 was onto the woodburner. This was a project within the project, and was an experimental version of a ‘rocket-mass heater’.

Rocket-Mass Heater

A Rocket-Mass Heater is essentially a modified rocket-stove in which the flue gases are redirected through a passageway, giving its heat as it goes, and then exiting the building through a flue-stack as normal. The passageway runs inside seating made of bricks and cob. Cob absorbs heat at about 1 inch per hour, and so is a good store of heat. Thus with 6 inches of cob heated by the flue-passage, it will take 6 hours for the heat to reach the surface, and the surface will be heated for 6 hours after the fire has gone out. In this particular design, the cob-seating is circular, in the centre of the Pyrapod.

The stove and circular flue-passage laid out. The stove is fed with wood at the bottom, flames shoot back and up the riser, and flue-gas is then pushed down into the circular passage and then round to the exit-pipe, seen here at top-right of pic. There is a damper between the stove and exit-pipe so that gases can short-cut to the exit when starting the stove.
The circular passage cobbed over. Also the stove now has an outer brick-liner to help insulate the riser for maximum heat build-up
 
 
The base layer of cob is complete

By 2017 the top-coat of cob had been applied to the rocket-mass heater, and a wooden floor (larch of course) fitted around it.


Also in 2017 the roofs were lined inside with an off-white cotton-canvas. The advantages of this material are that it is sustainable (it grows), lightweight, light in colour (so will reflect light around the space), and covers the area quickly and easily.

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