Hello,
I purchased some plans for a 16 by 24 queen post structure. Though I am a rookie at this I have read a lot and after getting the plans I have some concerns on the joinery (tons of dovetailed floor joists and purloins), short braces, the sizes of the timbers (almost all 6 by 6), and really tall knee walls, and finally a weird post to principal rafter connection instead of a plate. While its probably a fine plan (written by a respected timber framer) it seems it is no more work to build one with methods known to last for 100 years. That's the trouble with buying plans before you can really seem more than an outline of the building. So now I am thinking making my own plans based on the Sobon Shed, I guess I wasted my money on the plans.
Sobon says that the 8 foot space between bents can be increased to 12', which would give me the 24 foot long dimension I want. He says the rafter system works for up to 16 feet in width, but for widths more than 14 feet, the 8X8 cross beam should be increased to 8X10 (or add a center post). I would make it 16' wide and use an 8X10 cross beam no center post. He then goes on to state "if you go wider you need heavier floor joists too." I am thinking of a summer beam in the middle, with 12 foot 4X6 joists on two foot centers running parallel to the 24 foot length. His original design has 4x6 joists spanning 12 foot across the structure perpendicular to the length so it seems like this would be ok. Assuming this is ok, what should the summer beam dimensions be? I was thinking an 8 by 10 so the joist to summer beam connection on either side of the beam are 2 inches apart while till having a 4-inch tennon as show on the timberframeHQ website.
Sobon has a picture of a post and crossbeam on page 101, with this caption "The posts can be lengthened above the crossbeam to provide additional headroom in the loft." He doesn't say how much. Scaling off the line drawing on page 100 I think his design shows the post sticks up about 16 inches higher than the cross beam. How much higher is it generally accepted to go higher than the crossbeam (8x10) with an 8x8 post? The frame will be oak if that matters.
Finally, he doesn't show joinery for the loft, says you can throw 2-inch lumber across the bents for the shed. I will of course need joists. I think the tusk tennon or what Jim R. calls the tying joint into the crossbeam on bent 1 with the joist run over the top of the crossbeam in bent two would work nicely, and it seem that 4x6 have already been show to span 12 foot ok on 2 foot centers.
Please comment, your experiences and insights are greatly appreciated.
Matt
I did a 16x20 Sobon shed last year. 5x7 rafters, 8x10 ties, 5x8 joists across the 16' dimension. 12' to top of plate, 10' to top of tie. I think a "summer" sill beam and longitudinal joists is a good idea.
(https://forestryforum.com/gallery/albums/userpics/14240/IMG_20160515_190532558.jpg?easyrotate_cache=1463360862)
Adding a summer beam going from tie to tie will put a point load on the center of the tie where it will be carrying almost half of the floor load.
You may have to do some math and figure out what the loads will be and size the tie beam accordingly.
You can't just assume that an 8x10 will work in this configuration.
Jim Rogers
edit fixed it.
Dave: That looks great, thanks for the dimensions of the members you used. I do not have too many trees with 16 foot good logs but a lot of trees that will give a 12 foot log, That's why I was thinking of the joist configuration I mentioned. Do you have a scarf joint in your top plate or did you have 20 footers? Do you happen to have and plans for it?
Jim: in your last sentence you say "You can just assume that an 8x10 will work in this configuration." Did you mean to say "Can't" I ask because you mention calculations right before that.
Thanks Guys. Matt
Here's my Sobon shed. It's 14x20 with an extra 6 foot enclosed shed to the side (making the total footprint 20x20). Mine is 10 feet high to the plate, but I wish I had made it taller like Dave's.
(https://forestryforum.com/gallery/albums/userpics/26833/X_5.JPG?easyrotate_cache=1513121282)
(https://forestryforum.com/gallery/albums/userpics/26833/GEDC2629.JPG?easyrotate_cache=1505338778)
I didn't have to scarf any members. I don't provide plans, but this frame uses the same joinery as the one in the book.
Can't! :D
You've changed load and span on just about everything so a good idea to run through everything. That is a heavily loaded beam but it is a uniform rather than point load.
Great looking buildings! I love the look of stone foundation. My creek rocks are not big though so that's out for me. Thanks for the replies.
Yes, can't I just fixed my post.
Jim Rogers
Whoa, rereading this I can see it two ways. If you are calling the center bent tie the summer beam with 12' joists running from tie to tie and the center tie taking 50% of floor load then yes it is uniformly loaded. If the summer beam is running under the ridge with 8' joists running from girt to tie with summer(s) bearing in the center of the ties then they are indeed point loaded, with 50% of floor load.
The same load applied differently has a different effect. A point load at midspan produces double the bending moment as compared to an identical load spread out uniformly along the span.
The "summer" beam is in the floor system, between the bent 2 posts. It will support joists from each side. That way the joists will only be 12' long.
Quote from: Don P on December 13, 2017, 10:51:27 AM
Whoa, rereading this I can see it two ways. If you are calling the center bent tie the summer beam with 12' joists running from tie to tie and the center tie taking 50% of floor load then yes it is uniformly loaded. If the summer beam is running under the ridge with 8' joists running from girt to tie with summer(s) bearing in the center of the ties then they are indeed point loaded, with 50% of floor load.
The same load applied differently has a different effect. A point load at midspan produces double the bending moment as compared to an identical load spread out uniformly along the span.
I think the OP needs to clarify what he intends to do.
Jim Rogers
If you read it through, he intends to run an 8x10 center sill perpendicular to the ridge so he can use smaller 12' joists running parallel to the ridge. He has a lot of 12' logs available.
This is how I am interpreting what he wants to do. Not a great sketch, but one can get the general idea.
(https://forestryforum.com/gallery/albums/userpics/14240/20171213_114153.jpg?easyrotate_cache=1513183429)
Ok so this is on the first floor not the loft?
Jim Rogers
Yes its first floor and Dave's sketch is what I planned. Now I need 24 foot plates, lol. I guess I will have to scarf joint them I do not think I have any logs that good, although sometimes they are longer then I thought when I bring them down.
Thanks All