Step 4: * Timber Components - the roof!
Cut up the roof supports from 90mmx35mm (just like everything else).
4x2400mm lengths, each cut down the middle makes the 8 primary supports.
2x2400mm lengths, each cut into 4 makes the 8 secondary supports.
I live in a snow-free zone. If you are going to be snowed on you'll probably want a greater
roof pitch (eg make them 9' or 10' long instead of 8' long) AND stronger beams.
Roof/height Support lengths/pitch/angle:
A 15' diameter tent has a radius from the centre of 7&1/2' (which is shorter than the 8' length
of the recommended roof supports), When the roof is angled, the pitch is slightly longer than
the straight radius, so with a bit of math, depending on the actual pitch and size you choose, you might find that 8' is actually to short to reach the centre, or perhaps a bit long. That's ok because it doesn't have to reach the centre. The centre contains a 'hub' that can be anywhere from 1'(300mm) to 3'(900mm) across.
I could say I figured out the exact roof pitch I wanted, used some more math to get the required length of the supports, then used that to figure the size of the ring I needed if the
supports were 8'(2400mm) long, but I didn't. I decided I wanted a 1&1/2' (450mm) ring, and
that I didn't care what pitch the roof ended up at, so long as it wasn't flat.
I stood in the back yard with a half-assembled yurt and no centre ring, put a ladder in the middle, and propped the top ends of the roof supports on the top of the ladder (a 10' ladder I think), and
guestimated that it would be fine.
I built the ring and I put it together, and it's close enough. I could increase the pitch a little, but heck it works the way it is, so why change it?
You do it however you like. :-)
My First yurt was assembed this way, and it assembles fine, but it's more of an art to put together than a science. The next two yurt/s actually turned out a bit smaller (13-14' foot diameter), so I actually found it was necessary to cut up to a 20cm(6") off the roof timbers, so that they don't hang-out-over the edge of the yurt. That's OK too, and I find these are actually easier to assemble!.
Roof Support Connections:
Joining the roof supports to the centre 'hub' is detailed in the hub section, but joining the bottom of the roof supports to the top of the walls can be done in a number of fashions:
1) the first method I used, and the one I currently still use on my first yurt (but don't recommend) involves tying them down. Drill a 6mm hole thru/across the bottom end of the roof supports about 30-40mm (1&1/2") from the end, and tie a loop of strong woven cord (eg 4-5mm nylon venetian blind cord) that is about 150mm (6") across through that loop. The loop can then just be tied around top of the wall , when the support sits on the wall. I currently do that, and also extended the loop with about 450mm (1&1/2') of cord that can be lashed to the wall further down so the joint is secure (this bit works well enough).
2)What I did on yurt numbers 2 and 3 was to use a steel "pin" on the top of the wall, and have a holedrilled into the rool timbers at an angle matching the pitch of the roof. the steel pin on the frame goes into the hole on the roof timber, and creates a joint. have a look at the pictures, and you'll see what I mean.