Hello all:

Here is my 2 cents worth on this subject which I have taught many times over the years.

The placement of the braces to the outside of the historic timberframes did not happen without a reason, the main one being that the braces are in true alignment with the tenons that are on the posts which the braces are pushing against.

The tenons on the upper and lower ends of the vertical posts are placed roughly 2.25" from the exterior surface of the rough hewn timbers, therefore the pushing and racking of the framework due to wind pressure, etc. necessitated that the braces be placed in direct alignment ie: layout of the brace mortises would be 2.25" from the outside surfaces.

As the building wracked under wind pressures if the braces were placed in the centre as suggested above then the vertical posts would want to twist putting unusual strain on the frame and could cause a joint failure by snapping a tenon, or causing the framework to weaken.

The only place that braces are allowed to be placed in the centre of posts is where the through tenons are themselves in the centre of the posts.

A good example of this type of central layout could be in the centre bays of say a driveshed or barn where the connecting girts span from side to side. One that most people might relate to is the large anchor beams in the Old world Dutch Barns where The huge Tusk tenon passes through the vertical posts (centred), and the braces following suit are placed right in alignment in the centre of the post.

I might add here that some timberframers always offset the tenons no matter where the girts were in the building, while other centred the tenons where they could. Historically though all the outside timbers, posts, and plates and braces had their tenons and mortises offset to the outside, usually 2" from the exterior surface.

I personally have never found braces that were placed out of alignment with the corresponding layout of the tenons on their matching vertical posts.

I hope this helps to explain why braces are placed where they are in historic, or for that matter in modern frames by professional, or historical tradesmen, and I might say by engineering firms drawing up on site plans for construction purposes.
NH