Dan,
Can you please cite where Jack says that 4' max is OK between the tie beam and the plate on a kneewall? I'm not saying he's wrong and I don't have a copy of the book with me, but I'm surprised.

A quick calculation shows that an 7x7 with a 3' cantilever above the tie beam to the plate MIGHT be OK if there was no joinery, but after taking out the tie beam housing, mortise and peg hole it wouldn't (assuming an allowable fb of 1000lbs/sq.in, 65lb.sq.ft. combined load, 14' width and 30" rafter spacing). There's about 1500 pounds of roof thrust at the center post top and over 50,000 inch-pounds of moment at the tie beam joint.

In our workshop where we build this frame often, we always limit the kneewall to 2' max.

I'm not an engineer, and I could be missing something. God knows I hesitate to say Jack is mistaken, but he may have assumed something we don't know. But I do know it's dangerous to rely solely on rules of thumb without understanding the underlying principles. These types of calculations we cover in our Timber Frame Design course at Heartwood and I believe can be found in the Guild's two design workbooks. But it's always best to consult an engineer if in doubt, and by doubt I mean not knowing how to figure this out yourself. I realize that's why your asking here.

I remember one time I heard Jack say something different from what he said the year before, and when I asked him he said "Well, last year I was wrong!" And we didn't catch it then, did we? Gotta love the guy.