Rafter Ties

Started by burke, February 26, 2014, 01:41:47 AM

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burke

This is going to be another question about maximizing loft space, and, as far as I can tell, this has been asked many times before but I'd like a little bit more clarification than what I've been able to find so far.

I'm planning on building a 12x16 cabin, the height of the structure will be 8' with a 12/12 roof and built on skids. I'd like half of the length of the structure to be a sleeping loft. My rafters will be 2x8s nailed to a 2x12 ridge board and birdsmouth cut for full bearing on the 2x4 wall and spaced 16" OC.

I'm wondering if it's feasible to sit the rafter ties ( that would make up the loft portion of the structure ) on jack studs tied into king studs every 16" such that the top of the rafter tie ( if i can still call them that ) is flush with the bottom of the top plate of the wall. For the rafter ties added in this fashion, would it be worth while to extend them to meet and tie into the rafter tails ( planning on a 1' overhang ) as per the nailing schedule in my local building code for rafter tie + rafter connections. The remainder of the structure would have rafter ties near the upper lower third of the rafter triangle to make the living room area feel somewhat open.

Snow load is a concern in my area, I hope to minimize it with the 12/12 roof and metal roofing.

This is really only gaining me about a foot of headroom but, if possible, I'd prefer more to less. I don't want to spend a lot of money on this so if I end up placing my rafter ties on top of my top plate, so be it.

Any advice you fine folks have to offer would be much appreciated.


Don_P

Yes, by extending the dropped ceiling joists out to the rafter and connecting them per the heeljoint table you've provided the required tie to resist horizontal spread. Be aware while nailing to nail in the upper, unnotched portion of the rafter and possibly minimize the birdsmouth to provide a stiffer tail, at this size I doubt that is coming into play unless the roof load is high. The rafters are bearing on the vertical support of the top plate. The upper floor is supported by the jack studs. Should be good. At 12x16 have you investigated what it would take to create an adequate ridgebeam?


akwoodchuck

"The lyf so short, the craft so long to lerne."

Don_P

There does still need to be a tie between the CJ and the rafter equivalent to the heeljoint table, the stack of plates or even framing a roof on a plate on a floor is considered inadequate horizontal restraint. The first post on pg 2 of that thread is mine  ;D

burke

Thanks for the feedback guys.

I haven't looked into a ridge beam yet. I had considered it, but if this works it'l be easier for me overall. I'm going to run the numbers anyway, i'll let you know what i come up with.

Don, is there a maximum depth for the birdsmouth cut that i should be aiming for to keep the tail stiff?


Don_P

The minimum bearing requirement is 1-1/2", I'd stay close to that, and the less birdsmouth the higher the rafter sits. With a ridgebeam you can lift on up and get more headroom.