20x32 timber frame workshop questions

[BoyZinthewoods]

As the ground is thawing here in maine I'm hoping to get started on my little timber frame workshop that i milled last summer.  I went back and forth between bolt together post and beam and timber framing and have settled on the latter for more of a learning experience.   I could use some help....

light weight spruce frame, 6x6 posts spaced at 10 along the 20' gable ends and center and 8' along the eave walls, 3 20' 6x8 ties and 18' 6x8 plates scarfed to make the 32', 4x6 braces and a conventional 2x10 gable rafter roof, 9 pitch, no structural ridge, skip sheathed and metal roofing.

Here are my top 4 quandaries... any help is much appreciated.

- Any suggestions how far down the post from the plate i need to attach my tie beams?  I am thinking of using wedged through half dovetails on the tie beam/post so i can improve the mechanical connection (no pegs) and avoid any splitting from outward roof thrust hopefully allowing me to attach the tie beams higher up the post. 

-The building will have a loft/ceiling on half of it.  Are there any good ways to attach ceiling joists BELOW the plate (to gain loft headroom) where they can still act as rafter ties.  The joists are 12' and will overlap, resting on a summer beam in the center, but i cannot think of a good wall connection that will resist outward thrust.

-My sills will be 2x8 pt anchored to the slab.  any advice for a good post/sill connection?  steel?

-I've seen a bunch of different options for cutting mortises.  I was thinking i could just use my power drill and an auger bit but that seems a little tricky especially if i am cutting angled mortises for the dovetails.  Any suggestions for this?  It's a one time job so I cannot justify purchasing expensive mortising tools. 

Sorry for no drawings or pics...

[Brian_Weekley]

Welcome to the forum.

Thumbs up for trying a traditional mortise and tenon frame instead of a bolt together version.  The best advise is to take a timber frame course first--it will make your life a lot easier.  You really should have a final design drawn up first before you mill any wood.  6x6s are probably too small for a building of that size.  Generally, the tie beams should be about a foot lower than the plates so you don't weaken the joint.  You can certainly use a drill and bit to rough out mortises.  A bit and brace works fine too.  For the dovetail mortise, the angled portion can be made with a sharp chisel.

Where 'bouts in Maine?

[Dave Shepard]

Welcome to the Forum! I agree with Brian, a workshop is money well spent. I also agree that those timber sizes are probably too light. Especially the tie beams with a loft load. You may have to substitute some heavier parts, or use more of the smaller dimensions like a Dutch house or barn would have used, which was a post/tie beam/post, which is often called an H-bent, every four to five feet along the walls.

[BoyZinthewoods]

Brian and Dave,  thanks for the responses,  The course isn't really an option.  with 2 small kids, livestock, ongoing projects on the house and a need to get this building up before august, I'm not sure where id find the time (or money ).  I've got a final design but the weak points i've listed in my post.  Why do you say 6x6's are too small?  I've built and seen numerous post and beam buildings framed with 6x6 spaced at 10' or more.   

I just found out today that a good friend of mine has a chainsaw mortiser that i can borrow.... imagine that.  was kinda looking forward to drilling them out but... not that much.

I'm near Blue Hill

[Dave Shepard]

Part of what determine the size of a timber is the size of the holes you are going to put in it. A post in a pole barn type structure doesn't have any holes in it, but a post in a timber frame would have, at the least, a tie beam mortise and a brace mortise. If there were additional mortises that were not vertically aligned, then you would have to account for that in engineering the post.

[newoodguy78]

Was just curious as to the term skip sheathed, simply wide spacing of the roof boards? I've spent a fair amount of time building roofs and installing metal just haven't run across that term yet is all

[BoyZinthewoods]

Yes, sorry i have a bad habit of picking up other peoples improper building vernacular.  i'm thinking of using whatever boarding i have laying around as 'strapping' 2' OC

[S.Hyland]

Hi Boyzinthewoods,
    I agree that 6x6 stock is smaller than one would typically see for a frame this size. However, I don't think it is unworkable. As Dave Shepard mentioned, it will be important not to take too much wood out of any given part of the post. Since the design, will not have a ridge, the rafters will exert thrust on the walls, but with a 9 in 12 pitch won't be as bad as it could be. Your tie beam tenon should be a wedged and pegged through tenon extending a few inches past the post. This joint should be at least a foot below the plate but I would rather see it more like 18" because of the small post size. With a spacing at 8' it seems that it would do pretty well.  You will certainly want to peg that tie connection as well as using the wedged dovetail.
    I think that you really want to run your joists the other way (on the ties). I'm guessing 2x's framed right on top of the ties?
It seems to me like it would be hard to use the joists as rafter ties in this case, although I can see why you would want to. 
    For your post attachment you could have some C brackets made up out of 1/4" stock. These can usually be made inexpensively at a local fab shop. They have a hole at the bottom for anchor bolt connection and holes in the ears for lags. I use Zinc paint and good quality top coat on mine so they don't corrode.
    Good deal on scoring the use of a mortiser! That will be a great help. This should be a very manageable project for a first timer to cut and raise, good luck with it!

[newoodguy78]

Thanks for the clarification. That's a good way to do it. If I could make a suggestion it would be to put some diagonal bracing on the underside of the rafters. I think it helps when there's no plywood involved to keep the roof from racking. Not being critical at all just throwing out a suggestion. Good luck with the build. That's a fun size to do