Sill to Post Joinery

[kristingreen]

I've checked the glossary and I think that I'm using the correct terminology here but please correct me if I get it wrong.

The horizontal timbers that create the rectangle that becomes the perimeter of the floor are called the sills. Correct? I'm not sure if the timbers that the joists connect to are called something different than the ones that are at the end and run parallel to the joist... I've referred to both as 'sills'.

The corner posts rest on top of the sills where they meet at the corners.

This joint connects three separate timbers and has created some difficulties for me as I learn the basics of timber framing.

I've seen this joint done a number of ways but most seem to use a through tenon to form the corner and then a stub tenon at the bottom of the post fits into a mortise cut into the top side of the mortise of the sill.

My question has to do with the proportions of the mortises and tenons. I'll be using 6x6 cedar posts which measure in at 5.5 inches. If I try to use even numbers to make measuring and cutting easier, 5.5 inches divides nicely into either 2+1.5+2 (for a thin 1.5" tenon) or 1.75+2+1.75 (for a thick 2" tenon).  Is it better to have thin tenons or thick tenons?

And, what about pegs? I've seen some that use pegs for this joint and some that don't. Usually, a peg is used to lock in the horizontal joint while gravity keeps the post's stub tenon held down on top.

This screen grab from Wrangler Star's youtube video shows a thick tenon for the sill-to-sill joint but no pegs.

[kristingreen]

I wanted to add that I've read Jim's post about general joinery rules. In it, he states:

Most traditional layout was done with the layout tool at hand, which was the framing square. And as it has two parts, the body (the 2" wide part), and the tongue (the 1 1/2" wide part), most layout was one of these two dimensions.

Other standard rules for joinery decisions are that tenon size should be one quarter of the timber thickness. That means a 8x8 should have a 2" thick tenon and a 6x6 should have a 1 1/2" thick tenon.

This would indicate that I should use the 'thin tenon' approach that I described above, however, this seems to run against most examples that I've seen of through tenons which are thicker then the material that surrounds them when joined as in the picture below... as well as the picture above.

I'm concerned that since the force will be applied downwards, the strength of the tenon is important.

I look forward to reading your thoughts on this.

[Jim_Rogers]

Technically, you shouldn't be using a picture that belongs to another but since you screen captured it then is could be ok, as it is your screen capture.
Second Wranglestar is not the best teacher of timber framing. His joints are wrong lots of the time. He had not had any formal training in timber framing and therefore is making a lot of "beginner" mistakes.

Open ended mortises on sills is one example.

There are long sills in a frame that go down the long side of the frame. Then there are sills that connect the two long sills. These are called cross sills.
Usually we tenon the cross sill into the long sill and secure the cross sill tenon to the long sill with a peg. To hold it together.

One thing you need to understand is that there are "general rules" to timber framing. One of the requirements to make a "general frame rule" is the size and location of the mortise and tenon joint.

The engineers have told us that the tenon and its matting mortise should be 1/4 the timber thickness.
You are basically making a frame out of 6x6 but in real life as you can't seem to find full dimension timbers are 5 1/2 x 5 1/2. So we will still consider this a 6x6 frame.
That means your tenon layout should be 1 1/2" off the reference side/edge of the timber and then 1 1/2 thick. Your pegs should be 1/2 of the tenon thickness. So, in your case the pegs should be 3/4" in diameter.

Now, having said that your first "general frame rule" is:

1) All joints are laid out 1 1/2" off the reference edge and then 1 1/2" thick.

The next general frame rule you need to apply to all your joints is the timber size reduction rule.
What this means is that at each joint you need to reduce the size of the timber to the envisioned perfect inner timber. In your case it will be difficult to do as your prefect inner timber is going to be smaller than the standard one. We normally, when using 6x6's, say to the next 1/2" smaller in size. But as your timbers are already 1/2" under then you're going to have to compensate for that and go to the next 1/2" under the "delivered" size of the timber. So, it will be reduced to 5". This creates a
housing at the joints.

General frame rule #2 ) all timbers are reduced at the joint to the next 1/2" in size of the delivered timber.

Not all joints in your frame are going to comply with this rule. For example we don't reduce the brace tenon. But we do reduce the brace pocket and the post or tie beam will have a housing so that the post or tie beam end of the joint comply to the rule.


Here is a picture of a standard long sill to corner sill joint with the peg and post bottom moved out a bit to show the joint:



 

As you can see in the above picture neither of the mortises for cross sill or the post stub tenon go to the end of the long sill. You don't want an open "fork" joint at this location.

As for the post stub tenon it can be shortened to be just short enough to locate the post on the long sill.
If this shed is going to be sided then the siding is going to be nailed to the post and to the sill and this will hold these two timbers together. There usually isn't a need to "peg" the stub tenon of the post to the sill.
If you are concerned about uplift then you could run a long timberlok screw into the sill to secure the tenon to the long sill.

I hope you can modify your designs to do it correctly.

Keep asking questions.

Jim Rogers

[Dave Shepard]

The first step to learning timber framing will be to never watch anything Wranglerstar has posted.  All kinds of really wrong stuff going on there.

[kristingreen]

Thanks Jim! That's pure gold... I'll have to re-read it a few times to let it all sink in. I read your response on my other thread as well and I've got some thinking to do.

Rule #1: Don't watch Wrangler Star! Got it. Too bad really. He's a nice enough fellow who really tries. To his defence, he does say many times that there may be better ways to do things as he is just learning as he goes and sharing his experiences with us. He openly asks for his viewers to comment and offer suggestions so he is clearly open to receiving instruction.

[Heartwood]

Testing and experience have shown that a larger mortise weakens the mortised member more than the potential benefit a thicker tenon offers. Hence the 1/4 the thickness guideline that Jim mentions. Another is that the walls on each side of the mortise should be at least the thickness of the tenon, and the pin should go at least that far into each side. This is not always possible, and lapped joinery obviously doesn't follow this "rule". An open mortise and tenon at the ends of sills (and plates) can invite moisture (and rot) in. 

[Ljohnsaw]

I will be using a stub tennon for all my posts into the sills but my engineer is requiring one more item.  I am building on a FasWall block foundation (ICF-like).  At each post, I have to insert a Simpson STHD10RJ to hold things down.  They are basically a long flat strap with a hook at the end that rests in the concrete.  They will come up through the sill and attach to the posts with lots of nails.  Fortunately, they will not be visible on the finished structure.

[kristingreen]

OK... I've attempted to redesign my joint based on the feedback here and modified the design to suit 6x6 materials.

My stub tenon will be 1.5" x 3.5" (not 4" as I just noticed the mistake below) and 1.5" long. The corresponding mortise will be 1.5" away from the edges on both the long and short sides.

My cross sill tenon will also be 1.5" x 3.5" but 3.5" long. The corresponding mortise will also have 1.5" of material on two sides.

What does everyone think about these dimensions? Can I satisfy the general rules and still use 6x6 material?

[Jim_Rogers]

Looks correct now.

Jim Rogers

[Dave Shepard]

That is an awesome drawing!

[kristingreen]

That is an awesome drawing!

Thanks man! :-)

It's amazing what you can do with a big enough eraser. ;-)

[Dave Shepard]

What were your angles? 30° and 60°?

[kristingreen]

What were your angles? 30° and 60°?

Not sure what you mean by that. I just grabbed a pencil, ruler and a big fat eraser and started drawing. I don't think I have a protractor.

[Dave Shepard]

In an isometric drawing you pick angles from horizontal for the parts you want to draw, with verticals remaining vertical.

[kristingreen]

In an isometric drawing you pick angles from horizontal for the parts you want to draw, with verticals remaining vertical.

Cool! I'll try that next time. Thanks!

[pizza]

General frame rule #2 ) all timbers are reduced at the joint to the next 1/2" in size of the delivered timber.

Hi. If I'm building a smalllish timber frame using 4" x 4" (actual sizes) timbers, what would the reduction be to get to my ideal timber within? I saw that one of the rules in the post for 6" x 6" timbers was 1/2" reduction at the joints.

My lumber supplier says their 4" timbers are generally accurate but 1/8" plus or minus is what they usually tell customers. THey couldn't give a spec on straightness.
and the lumber is green. I'm considering white oak. As they have a choice of red or white oak or poplar. Since these timbers will be exposed to the elements (it's a wood shed). 

Thanks.

[Jim_Rogers]

1/2" under even with 4x4's is good to use. And white oak would be best for posts that would be exposed to elements.

Jim Rogers

[pizza]

Thanks! Based on the rule of using 1/4 of the lumber thickness, I will also be making my tenons and mortises 1" thk. 

Should I make the tenons and mortises also be located 1" from the reference surfaces too?

And how much relish should I leave? 1" OR 1.5"? And as far as the pegs go is 3/4" too much or should I go with 1/2" diameters?

Thanks in advance.

pizza

[pizza]

Can someone answer my question from my last post (reply #17 above) on this "sill to post joinery" topic.

Thanks!!

[pizza]

Won't the stub tenon in the post contact the tenon in that cross sill? Will the mortise in the long sill for that post's stub tenon break through to the mortise for that cross sill?

Thanks.

[Jim_Rogers]

Should I make the tenons and mortises also be located 1" from the reference surfaces too?

Yes offset 1"

And how much relish should I leave?

At least 1 1/2"

And as far as the pegs go is 3/4" too much or should I go with 1/2" diameters?

Follow standard rules 1/2" diameter; larger takes out too much wood and weakens timbers.

Won't the stub tenon in the post contact the tenon in that cross sill? Will the mortise in the long sill for that post's stub tenon break through to the mortise for that cross sill?

Yes, most likely the two mortises will connect but trimming the post stub tenon by 1/8" and the cross sill tenon by 1/8" will allow some room. Trim during fit up until they don't touch.

Jim Rogers

[pizza]

thanks!