Help: Circular Roof Angle?

[Gerroffit]

Hi, I wonder if anyone can help? I'm making a 16-sided wooden building, 15 feet across. The roof will be made of 3"x2", with a fairly light covering, no slates, etc. The corner posts alternately support hip, then half rafters. The half rafter is about 3' 6". The 8 hip rafters stop short of centre by 9 inches and have a further noggin between each at this end - this simulates a kind of yurt look with a centre hexagon. Roof angle is 65 degrees. My questions are: is this acceptable as a roof angle? How much lower could I safely go? Does this sound like good construction?

Any info appreciated

G

 

[cmother1]

Do you mean 25 degrees (ie 90 minus 65). The lower the degrees the flatter the roof gets in normal notation. 25 sounds OK to me.

A plan of your construction would be useful. 16 sides sounds inordinately complicated to me. You'll have to tie the cross members at the eaves to the hip timbers really well if you're to avoid the roof flattening out under its own weight. What do you intend to cover it with? Assuming no internal supports the lighter the better, I'd say.

 

[Gerroffit]

Do you mean 25 degrees (ie 90 minus 65). The lower the degrees the flatter the roof gets in normal notation. 25 sounds OK to me.

A plan of your construction would be useful. 16 sides sounds inordinately complicated to me. You'll have to tie the cross members at the eaves to the hip timbers really well if you're to avoid the roof flattening out under its own weight. What do you intend to cover it with? Assuming no internal supports the lighter the better, I'd say.

Thanks for the above, I'll try and upload images of what I'm doing.
The 16 sides is a bit toppy I agree, but I'm trying to get a near circular look. The trouble is too that it's a semi-portable building, made up of handful of pre-made components that can preferably be carried and erected by just one person, so cutting it all into 16 is a lot easier on the end-user.

I have the timbers tightly fitted into the uprights, and fixed with a bolt. The uprights will also have a hawser running through the top of each to help take the outward stress (along with actual horizontal beams tying them each together at top and bottom). I was hoping that the downward weight would force the rafters down and hold the cone together, preventing it from collapsing inwards, so as long as I tie them in sufficiently you can't see this as a problem?

Thanks again, this is really useful.

G

 

[cmother1]

That's a very ambitious porta-shed you've got there. I hope it's a strong one person who'll be carting it around.
Something like the hawser you mention will be essential to keep the roof nice and pointy. It's the same method Christopher Wren used to keep the dome on St Paul's from imploding. You're in good company.
Hard to see, though, how one person could hold the whole structure in place while tensioning the wire - you'll probably need a temporary prop for the centre while doing this.
Please post some photos - it sounds like a really interesting project.

 

[Gerroffit]

That's a very ambitious porta-shed you've got there. I hope it's a strong one person who'll be carting it around.
Something like the hawser you mention will be essential to keep the roof nice and pointy. It's the same method Christopher Wren used to keep the dome on St Paul's from imploding. You're in good company.
Hard to see, though, how one person could hold the whole structure in place while tensioning the wire - you'll probably need a temporary prop for the centre while doing this.
Please post some photos - it sounds like a really interesting project.

I didn't know that, interesting.

If you can imagine that it's sixteen uprights bolted together with horizontal 3x2's top and bottom, and braced by diagonal 3x1. There will be enough hold in the frame to keep it all together, but I'm hoping that the hawser will just take the strain off it at higher wind pressures as the roof starts to give.

All of the units that make up the building can be carried and installed by one person, without the use of a screwdriver or powertools, hopefully in a few hours. The heaviest part is actually one of the floor sections, but its still very managable.

I realise that what I'm doing is a bit of overkill, but I wanted this to look and feel sturdy, like somewhere to live and not just a 'hut'. I'll post bits as it comes together.

G