Timber Joinery Questions :: Kitchen Remodel

[Troy_T]

Hi gang. I am new to the site and am attempting a timber kitchen remodel. I have a few questions which I'm not finding answers to in any of the books I've read by Ted Benson, Steve Chappell or Jack Sobon. Hopefully someone here can shed some light.

The house is an A-frame with a lofted second level. The kitchen is on the first level, underneath the loft. The plan is to replace the three interior walls of the kitchen, currently 2x lumber, with nice douglas fir timbers. There will be a total of five posts (7.5" x 7.5") and four beams (7.5" x 9.5"). The top of the beams will line up with the top of the posts. The connections will be straight-housed mortise and tenon joints. (See layout images.)

Typically the tenon is the entire height of the beam with a matching mortise in the post. In my case - with the beams located at the top of the posts - it would mean that the mortises would extend through the tops of the posts. Is there a rule of thumb for how far mortises should stay from the top end of the post? Would an inch be enough? Is there potential for joint failure or twisting when a tenon doesn't extend the full height of the beam?

I could also use some help with tenon sizing and layout. I've seen that for housed joints a 3"-long tenon can be used (Tedd Benson's book). Does this sound correct? Will that be enough for the pegs?

Thank you for any input/insights which you may be able to offer!

And Jim R: thank you for the informative "General Rules ..." and "Standard Procedures ..." posts - both very helpful!

~Troy



  

 

[Troy_T]

Anybody here know if it's acceptable to trim the top of a tenon like this? So the mortise doesn't cut through the top of the timber.

Thanks!

 

[beenthere]

Seems that will very much depend on what your loads are on the three members and what the joint design strength needs to be for the construction.

If no load... should hold together.

But if there is load on that cross beam... and torque at that joint ???  doubt it.

But Jim and others will be along to give better timber framing comments.

Can you tell a bit about what the design is and what you expect of this joint?

[Brian_Weekley]

Welcome to the forum.  I think you might need to provide some additional information.  Are these load-bearing, or mainly for looks to define the kitchen area?  It sounds like maybe you don't want to see the tenons on top of the posts from the loft above?  Is there anything being supported above the beams?  Why do all the beams need to be in the same plane along the top?

[Troy_T]

Hi Brian,

Thank you for the reply.

These additional photos show what's going on a bit better. The beams will be supporting the joists for the loft and the side with 3 posts in a row is load bearing.

A structural engineer specified an 8" x 8" beam placed across the top of the three posts. I decided to go with an 8" x 10" nominal and a local timber guy said that I should house it in the posts versus running it over the top so there will be a 1" shoulder at each housed joint.

Because the joints are located at the top of the posts, it dawned on me that it's probably not the best idea to cut the mortises all the way through the top. I'm curious if anyone else here has run into this issue and if so, what was their outcome?

Thoughts?


  

 

[Troy_T]

Hi BT -

Thank you for the reply.

This will be load bearing but there shouldn't be much torque. The posts are 8" x 8" nom with a 1" shoulder to house an 8" x 10" nom beam for an 8-foot span. Joists 16"oc which support a loft will run perpendicular to the beam.

Thoughts?

[Heartwood]

Right idea, but wrong orientation, in my opinion.
The beam should go over the post, with the tenon on the post. More efficient for the loading. And trim 2" of relish off the post tenon so the mortise in the beam isn't open.

[beenthere]

Troy
When seeing your other thread, I assume the two fit together (maybe the admins will combine this with the other). Makes more sense when seeing the overlay's in the remodel thread.

[Troy_T]

Heartwood,

Is this more along the lines of what you're thinking?

 

[fishfighter]

I would go that way.

In my timber/stick build, that is how I did things.



 

[Carpenter]

Yes, the beams on top of the posts would be better.  But, how would you get them in place with the loft already built?  There are ways of course, but as this is a re-model, that has to be taken into account.  I think it's more practical in this case to build the supporting wall according to the original drawing. 

[Heartwood]

Hi Troy,
Not exactly the right orientation;
Mortises should always be parallel to the grain of the mortised member, so the beam on the left has the tenons going the wrong way. The post should go into one set of beams and the other perpendicular beams should tenon into them with a high tenon. I suggest looking at Jack Sobon's Historic American Timber Joinery book (available from the Timber Framers Guild for $15 - a bargain) to get numerous versions of such a 3-way joint.
Also, you don't show the relish removed from the side of the tenon to avoid open mortises at the corners (not critical but desireable), and the brace tenons are impractical, if not impossible. The short side of the brace tenons should follow the slope of the short side of the brace. You'd probably figure that out when you tried to cut one.

[Heartwood]

To get the assembly in place in an existing room, I would try lifting the joined beams into place with temporary posts then swinging in the four corner posts under them. This would require cutting the posts a bit shorter (maybe 1/2") and then shimming them up tight, and also a tapered tenon on the top. If new flooring is not installed yet then that can cover the shim, if the existing flooring is staying then a piece of trim can cover it. Braces can be preinstalled hanging from the beams and the posts can swing onto the lower brace tenons.
Just one idea....