Plywood Pentayurt and New Zealand Building Codes

22 May

Many attendees at Burning Man, the annual alternative party in the Nevada desert, have discovered the useful qualities of a temporary building design called a hexayurt. This design (invented and open-sourced by a chappie called Vinay Gupta) is notable for a very efficient use of materials. It cunningly makes use of either whole, or diagonally cut, sheets materials in the very common 2440 x 1220 (eight foot x four foot) size.

Here’s a typical hexayurt (image stolen from http://hexayurt.com/), in bright reflective materials for hot weather conditions.

Now, we hope to move out of town within the next year, and with all the challenges to our budgets, I’ve been thinking about building a cheap shed based on hexayurt designs.

I’m by no means the first to think that, for examples this guy built a nice looking shed out of oriented-strand particleboard for $132 in materials.

However, this is New Zealand, land of bureaucracy, forms, and nanny-state control. The council wouldn’t be happy with a structure like this and would insist it be ripped down (though they might be reasonable about short term use). But, tucked away in a government document dbh-guide-for-building-work-consent-not-required I spotted a section that went A building consent is not required for the following building work … does not exceed 1 storey, does not exceed 10 square metres in floor area …

This looks promising. Unfortunately, the most common hexayurt designs run to 166 sq feet and my 10m2 limit is 107 sq feet. There are other designs, including the pentayurt (which, logically, has 5 sides and coincidentally has steeper angles which handle snow better). The standard pentayurt runs to 110 sq feet – just too big.

A little fiddling with numbers, and a willingness to make a few more cuts, and I’ve got a possible design.

If I shave 50mm off one end and 25mm off one side, of each 2440 x 1220 sheet for the roof triangles, then cut them diagonally, I end up with triangles 2390 x 1195, ten of which form a pentagonal pyramid covering 9.8m2. For the vertical walls, five more sheets have 80mm cut off one end, leaving rectangles 2360 x 1220, which form a pentagon inset by 20mm from the roof (to get rain drip eaves) with a floor area of 9.6m2. I drew a plane across at 1800mm (about 6 feet up), and a very respectable 4.3m2 of the floor space is higher than that – plenty of headroom.

The good thing about all this – I saw someone selling sheets of exterior plywood (11mm, H3 treated) for $29 each. That’s $290 for the basic structure. There would be extra costs, and it would be pretty primitive, but everything I could store in a cheap shed would be more space in the house – and the house is expected to cost well over $1400 / m2.  I’m mighty tempted.

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