Hello,
I will be building a timber frame pavillion( about 12'w x 16'l). All the main frame components will be 8" x 8" and made from med or hard wood species. The tie beam will be joined to the corner post below the top plate. The joint will be secured with two pegs. What should be a minumum distance that the tie beam( with through tenon) should be below the top plate. I dont want the corner post to eventually split above the joint if the tie beam is too close to the top. Any help would be appreciated.

In the History American Joinery series there are section about the tie connections.
One is "tie at the plate," and one is "tie below the plate."
This series is available from the guild home page. And you can download the sections to view as pdf files on your own computer.
Or you can buy the book for $10 from the guild store.

You may find lots of examples of tie to corner post connections there. One of these may give you your answer.

Are you concerned about uplift? as it is a pavilion.

Jim Rogers

Common rafters? Ridge or no ridge? If a ridge, will it be supported or unsupported?

Welcome Steward;

That is an interesting engineering question thus Tim's questions about the rafters. The roof pitch matters also. It is a small building so relatively small loads. Another factor is the species of wood used for the posts, though I am not sure where to find engineering data for the splitting strength of the different species.

I study historic framing and so I tend to answer people's questions with references to what I have seen done before the early 20th century. Generally this type of framing has a minimum distance of eight inches or more. More than two feet and the posts typically start bending outward. The tie beam joint relies entirely on the pegs unless you can extend the through tenon and add a wedge or two.

If you want to keep the tie beam as high as possible you could use a rare type of tie beam called a head beam and put the tie beam immediately below the plate. Here is what I mean, look at page 252, diagram 6.5:

http://books.google.com/books?id=J9qoVN6...arn&f=false

Jim

Hi Jim, nice book, I should get a copy some time, put it on the book list. It says pages 249-351 are not shown in the link?

Same for me, I couldn't access the page you mention.
Can you show us the diagram?

Jim Rogers

Thanks for the reference Jim. What do you mean by "uplift"?

Timbeal,
Common rafters will be used with a ridge beam. The ridge beam will be supported at each end with a small " queen post" above the tie beam.

Uplift is the effect when a structure that is open on the sides (although not necessarily only such structures) behaves like a wing. The wind blows through and generates lift through the roof. If your structure is only engineered to resist downward force (for example, unpegged stub tenons at the top of the posts into wall plates) then it's possible for the roof to lift clean off!

Steward, it seems you should have no problem with the knee wall cracking above the dropped tie, as there should be no thrust on the walls. The loads will be exerted straight down, into the ridge and the top plate. If you did not have the ridge supported then there would be thrust on the wall.