Hi Toivo,
This is a particularly difficult joint to decipher. The purlin "extension" (to the left) is a short length maybe 3 or 4 ft long that is tacked onto the end of an 18 ft boxed heart elm purlin. Its very difficult to say whether this is original or added later because of the smoke blackening and limited access around the joint but it is positioned above a fairly narrow 6 ft wide bay (at ground level) which is still open to the fully hipped roof. To determine exactly what is happening inside this joint would require a little more in the way of joint forensics and unfortunately that window of opportunity has now closed. This is not a perfect world or a subject where everything is or can be revealed on demand in crystal clear detail.
I rather like the full text version of advice clarification given by Donald Rumsfeld :-
"... as we know, there are known knowns; these are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns - the ones we don't know we don't know1...”
Are you now ready for the analysis ?
The large peg that has blown the joint is the "singles" rafter peg and hence the 2 other smaller pegs (to the right of the large peg) appear to relate to the scarf joint. These 2 pegs have been driven from the outside in. To the right of these 2 pegs there appears to be 2 peg hole "shadows" which might relate to this joint and if they do then these would be for 2 pegs driven from the inside out. This might well be a simple step lap joint with the mating faces in the centre of the purlin in a plane parallel to the roof. We must keep in mind that there might well be other features of this joint that we cannot currently see.
Which stage in "Rumsfeld's progress" have you now reached ?
Maybe Mike could produce an "X-Ray" specs view of the likely configuration of this joint using Sketchup.
Regards
Ken Hume
