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I'm planning to frame a 12' x 16' floor. Should the joists be 12', and the beams 16'? Or vice versa?

More detail: 4x4 posts on concrete piers; 12' x 10' will be enclosed; 12' x 6' will be a covered deck. I'm using the county's standard loading of 40 psf live/ 10 psf dead.

EDIT: adding a 3D view (click for full size)

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Glad to hear you are building something with 4 sides. lol –  shirlock homes Apr 10 '12 at 11:42
    
Ah ha, I knew there'd be something round in the plans! :) –  BMitch Apr 10 '12 at 19:06
    
nice touch Jay. I'd go with the 12 foot joists and center under beam on this one and 16 foot plank decking, since it is not tied to the yurt with joist hangers. –  shirlock homes Apr 10 '12 at 21:47
    
Are you gonna live in this igloo? lol –  shirlock homes Apr 10 '12 at 21:49
    
Thanks for the advice, all. I'm using 3x 12' beams. The middle one will be offset to help the deck sit lower. Who's answer should I accept? –  Jay Bazuzi Apr 10 '12 at 23:59

2 Answers 2

Typically you run joists the short direction for the maximum load bearing capability. Depending on how you're designing this (I'm not skilled in yurt construction) you may want to make the 10' and 6' your short spans with a beam separating the indoor/outdoor parts.

Another consideration when it comes to deck construction is getting the proper slope for water to run off, and that is easier with the joists run perpendicular to the wall of the house.

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Thanks @BMitch. This isn't yurt construction: it has 90 degree angles! Since the deck is covered, I think the slope isn't a big concern. –  Jay Bazuzi Apr 10 '12 at 2:38

I'm not sure exactly what the orientation of this floor is? It is also common to split the 16 foot span in half with a center carrier beam, thus allowing you to use 8 foot joists on either side. The advantage to using two sets of 8 foot joists as opposed to single longer ones is that you can use smaller less expensive stock, and you can more easily control any wain or bowing typical in longer stock. Using a center beam also gives you a good structure to add additional center concrete post supports. This is also done by running a perpendicular double beam half way under the 16 foot joists, which gives the same support as using two 8 foot joists with a center support.

Another consideration is what kind of material and orientation you want to use as decking. If you are using planking, the aesthetics may be a determining factor. Got any drawings we can look at?

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Added a drawing for you. –  Jay Bazuzi Apr 10 '12 at 19:00

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