outdoor kitchen pavillion

[Mike KY]

Hey folks, I'm building an outdoor kitchen on the farm where I work. I have a few years of building experience but have never designed a post and beam type building such as this. The building will be a 12x16 gable with a 10' shed extension. There is an existing 13x16 foundation that I'll be building on, and the shed roof will extend over the ground, to shelter a picnic table to two.

picture can be seen here: http://3.bp.blogspot.com/_GaZUiMlS2Tg/TSOISs6z4SI/AAAAAAAAALo/9h_gL5wjwqM/s1600/Kitchen_current.jpg

The posts and beams are 6x6, probably white oak, but maybe eastern red cedar. The roof framing will be something else, maybe cedar, but not sure yet. Rafters are rough cut 2x6, and I'm using angle iron to attach posts/beams. a simpson joist hanger for the tie beams, and T straps at the beam lap joint. I'm pretty confident about the design, I think the spans are all ok, but the one question I have at this point is about the roof framing, and the rafter ties in particular. I have two 4x6 tie beams on either end of the frame, and 4 2x6 rafter ties every 4' in the mid section of the roof. I imagine this is sufficient to counter rafter thrust, but I'm not sure. 20 psf snow load here, but usually no snow really.

I'm just hoping some folks with more experience would be interested in discussing my framing plan, and hopefully catch any outstanding mistakes on my part. Thanks!

[MountainDon]

[Don_P]

If you think about it there is no reason the gable ties need to be at the same level as the plates that carry the rafters. The joinery would be less cluttered if they were either dropped... or I would set them on top of the plates. I'd set another raised plate above the midpost. I'm just talking at this point without having checked anything but that might be all the tie needed with the plates acting as beams. It would be a good timberframe project 

[Mike KY]

Thanks for the suggestion Don. I have thought about tying on top of the beams. The only reason I left out the middle tie beam was to simplify things around the lapped beam, but of course it would be simpler to just have the tie on another level. Do you think I need the rafter ties with three tie beams?

And yes I agree, this would be a great timberframe project. But this building really needs to be completed this winter so I can spend the spring working on the kitchen space, water, and electricity. Plus I have neither the tools or training to do timberframe. I hope to spend time this coming year helping a friend build a small timberframe house, so maybe after that I'll be comfortable doing it myself.

[Don_P]

Mike what is the pitch on the gable roof?

[Mike KY]

It's 6:12, 2x6 rafters 24" o.c. I plan on installing 1x4 purlins and corrugated metal roofing, would prefer not to sheathe with plywood. I think I should have wind bracing under the rafters as well, or maybe I can find a roofing panel that's stiff enough to prevent racking.

Has anyone framed a roof with ERC? I feel like using decay resistant wood because it's an open air building, but have no experience using cedar other than for fence posts.

[Don_P]

 I'd opt for white oak for the plates, full length if you can. Use your best sticks on the side carrying the roof and shed roof combination. I wouldn't use erc for the plates it is not a very strong wood. It would work fine for the posts. for rafters I'm a bit leery and for purlins I don't know if it'll react with metal... the tannins in oak certainly does though.
At 6/12 the center tie would need to restrain 1440 lbs tension. That is in the 5/8" bolted 1/4" thick angle iron range. If the tie extends over the plates and has a notch that drops over the plate "hooking" it and enough relish beyond the notch where that cannot shear off that will take a good bit of it as well. I'm not sure there's enough room to make that work. Another way, timberframers cut a dovetail key in the bottom of the tie and top of the plate and used that to restrain thrust. Think about the time to do that vs drilling and bolting, it may be a wash. If the rafter at the tie is white oak and has 13 16d sinker nails from rafter to tie that takes care of it as well. Since the plate is a 6x6 section it can act as a horizontal beam between ties and is able to restrain the 1440lbs horizontal. The plate at the gable roof shed roof has about 2640 lbs vertical.

[Mike KY]

Thanks for your help Don! I figured there must be a reason you don't see ERC being used for beams and rafters. I have been planning on doing most of the work solo, and that's why I split the plates in two. I'll certainly need help if I use full plates! I'm assuming in your calculations that you replaced the rafter ties with the center tie beam, is that right? I actually have a few white oak 2x6's on hand, I wasn't planning on using them for the entire roof, but maybe just for the rafters at the tie beams, and use something lighter for the rest of the rafters. The sawmill nearby suggested I use yellow poplar for the rafters. And I do like the idea of dovetailing the tie beams in. I built a very small post and beam structure to shelter an outdoor oven this summer and cut a housing in the plates at the posts, and toe-screwed, seems I may be taking baby steps towards TF joinery.

[Don_P]

I certainly don't consider myself anything more than a carpenter. I'll use any method that is desired or seems to work for the situation. TF was nothing high falutin in its heyday just carpenters making shelter with what they had.

I do like poplar 2x framing, its in the neighborhood of SPF strengthwise when using clears or small knots. It doesn't make very good boxed heart timbers. Avoid using a board with the heart in it, chalk a line and rip it down the heart, it will spring apart as the growth stress releases then chalk new straight lines on those two pieces and go again.  The rest of the sticks will pretty much tell you what they wanted to do, they stress released on the mill as the log was sawn. The piece with heart in it still has trapped stress on each side of the heart. In a big timber you usually get a large check.

Powderpost beetles love poplar, especially the white (starchy) sapwood, they also like the sapwood of white oak and about any part of red. I've taken to dipping my wood in a mixture of 1 lb solubor (farm supply) per gallon of water. You can paint it or spray it as well, but I soak it good. This is good for any wood consuming bugs and decay fungi as well. Is low tox to mammals, like a salt, and does not corrode metals. My barn is made of untreated poplar and the ppb's are eating it alive. I've had some dipped poplar under the shelter stickered for 2 years, they haven't touched it. Not very good environmentally but they won't touch used motor oil either. A heavy coat of well maintained paint will also keep them out, they can't bite through it. As soon as they find a crack though, that's why I finally moved to dipping everything. Part of it is once they know where a woodbutcher lives they move in like uninvited relatives. But if you're near woods, they're there.

Kinda sidetracked there 
Yes I replaced the (code) rafter ties with the end and center tie beams, so 3 ties. You can get away with this because the 6x6 plate acts as a  beam in both the vertical and horizontal directions. It can handle the 2640 lbs vertical on 8' spacing so can easily handle the 1440 horizontal thrust on the same spacing. It's actually taking the common rafters' load axially, 1932 lbs down the length axis rather than either the vertical or horizontal components. These are all describing how the same load is pushing in the vertical, horizontal, and axial directions. I'm not an engineer but understanding the structure is part of my job. So, this is all worth exactly what you're paying for it.

2 guys can handle a 16' WO 6x6 up ladders ok. Scaffold is better, set it on the scaffolding, hop up and lift onto the posts. I've been moving some 16' 8x8's around in the yard and shop and they will not be grunted up. I can handle one end at a time "up to my lunch" but that's about all that is safe. They are getting close to twice the volume of a 6x6, 64 sq" vs 36 sq".

Do you have Jack Sobon's "Historic American Timber Joinery"? If so, look at chapter 2, tieing joints at the plate, for a variety of options, if not, I'll dig up the link, good stuff.

[Mike KY]

I've never custom ordered lumber from a sawmill before, and I've been wondering about things like box hearting the timbers. Is it reasonable to request all box hearted oak timbers and heart-free poplar 2x's? I've never thought about issues with bugs, but i guess I should give it some thought. thanks again for your help with the loads, and no I've never read Sobon's book, I should check to see if the local library has it.

[Don_P]

Yes, that would be a reasonable order.
The Sobon book is also a free download here;
http://tfguild.org/joinery/joinery.html