Tie-at-plate . . . asking for trouble?

[Lex]

Hi all,
On a shed i'm designing i'm hoping to run the tie beam and plate at the same elevation on the posts to save on headroom for the interim frames.
At risk of breaking all the rules that should not be re-invented . . . how about the sketch below? Its not a million miles off some of the joints in Jack Sobon's "Historic American Timber Joinery" and I intend to use rafters and purlins so the tension on the tie-beam dovetail shouldn't be huge.

Not sure i've got the hang of adding pictures yet, so bear with me.

[Dave Shepard]

Welcome to the Forum. I'd be worried the dovetail wood loosen when it dried.

[Planeiron]

What about an English tying joint? Would that give what you're looking for? Everything comes together on a similar plane. I'll try to post a picture later but should be in the Sobon text as a very early example before newer joinery techniques were developed. I've used this joinery last year for a frame.

[Lex]

Welcome to the Forum. I'd be worried the dovetail wood loosen when it dried.

Thanks Dave, a bit of shrinkage might be OK as long as it didn't allow the tie to drop off the 1" lip (apologies for the terminology . . ) on the post - but yes, an issue.

[Lex]

What about an English tying joint? Would that give what you're looking for? Everything comes together on a similar plane. I'll try to post a picture later but should be in the Sobon text as a very early example before newer joinery techniques were developed. I've used this joinery last year for a frame.

Would love to see a few photos, i did have a look at this in Sobon . . just looks like rather a complex animal for what i need. Maybe i need a combination, tie-below plate on the gable ends and then tie at the plate for a couple in the middle. I'll post a pic of the whole structure as there are a few more issues . . . .
Thanks for the input.

[Planeiron]

It's a bit intimidating at first but it really only involves an additional tenon perpendicular, inboard to and a bit higher up to the one in the sketch in your post. I did a practise piece with an offcut before using the final stuff. I really wanted to have a life size guide to see how the tenons related to one another that I could refer back to. It also gave me a chance to try cutting the lower tenon (which would be the equivalent one on your sketch) which is the trickier one (I think anyway) and I didn't feel I needed to practise the upper tenon which is pretty ordinary so it's not in the mock up piece.

Anyway, this joint also lets you tenon in a rafter so you've also got a truss sorted in one go.

[Brad_bb]

Of course I'm sure you know that the reason for not putting them at the same level is the loss of strenght by removing so much material from the post.  

I prefer to not have them at the same level.  

Another possible solution is the use of gunstock/jowel posts.

I don't like dovetail joints.  As Dave pointed out- shrinkage.  A little more work to cut, and your fit after shrinkage may loosen.