Hello all,

is scarfing over a post acceptable? It seems to me that a scarf is most common over a brace - what is the reason for this location? My guess has often been that when the braces are loaded in C&T, the tendency would be to try and 'dislocate' the scarf if it were over the post???? If this is the case, then the lower blade should catch both braces and the post tenon?

Thanks folks,
Brock

Good morning Brock,

I my opinion you should be able to put the scarf joint close to a post because of leverage.( one beam has to hold the other) It does not matter if it is right on top of the post or a within 2-3 feet of it. I think that right on the post might even be better because that would put less weight on either beam since they will not have to hold each other and instead rest on the post.

If it were the case that the c&t of the braces would dislocate the joint if one were to put it right on the post then same would be true if it is not. You still need to attach the beam(whether it has a joint or not)to the post via t&m. So now if the braces are putting a load on the beam it cannot dislocate.

Just my two cents.

Best Regards Enrico

The scarf joint is best located where stresses (bending and shear) are lowest, and this usually falls over the brace, not over the post. This is illustrated graphically in Jack Sobon's "Timber Frame Construction" (the red book).

Jim Rogers posted an excellent description of scarf joints somewhere else on the Internet but I can't find the link. As I recall it was recommended that the joint be at the beam's point of inflection. (Makes sense to me, having tutored newbies in basic calculus). Hopefully he will chime in and explain in more detail.

I agree with the other posters, Brock. A scarf joint weakens the timber in bending strength. The greatest bending forces usually occur right over the post (bending up), and also mid-span (bending down). That's why the scarf is usually placed somewhere in between. The stress over the post is higher than the mid-span stress, as it results from a point load (the post) rather than a distributed load (like a floor). Dan is talking about a diagram on pg 96 of Sobon's book, which sums this up better than I can with words. CB.

post by Brock Smith Yes. I think this is what you're talking about.

I do not like the brace triangle to be interupted by a scarf joint. But, I have also seen a lot of scarfs in old barns located over the posts. They held up just fine, so I'm not convinced that it's that critical. A scarf over a post with a through tenon to locate both halves, would not separate when the braces went into compression. Tom

Let's assume that there is a downward force applied to the beam on the left in the illustration. That would cause the other beam to bend down also and would put compression on the brace. Now the brace might be, and in all likelihood is able to support that load even though its real design purpose is to stiffen the frame. So the question is why wouldn't you want to put the scarf joint above the post. That way both beams end up in the same position and the braces can also add additional support to both beams equally well. In addition to that you would be able to put a through tenon on the post which can secure the scarf as well as held the beams in place/down(pegs).

The right beam in the drawing would be the stronger one since the one on the left is scarfed onto it and only supported by the blade and the brace but not the post.
Try to imagine the same drawing without the braces. Now where would you put the scarf joint?

Not sure if I am bringing my point across!?

or over the post

I have done it both ways

@ Tom,

aside from the reasoning for having it over the post or the brace. I just like the over the post version simply because it looks more balanced/ symmetrical.
But time has proven that both versions will work.

Thanks guys, I really appreciate the info. I checked page 96, and Sobon's description helps out.

Now if I may, I'd like to ask further. What about scarfing a structural ridge? King post truss, pitch is 30 degrees, span is 22ft, common rafters are to rest on top of the ridge. I think I can get away with interupting the plates at the posts and omit the scarf at that location.

Geez. I really have to get on the computer drafting bandwagon. Does anyone here still user a big ole' klunker drafting board?

Thanks again,
Brock