One corner was invaded by carpenter ants many years ago, and the bottom ten feet and the upper three feet were pretty well destroyed. It is a tribute to the overall sturdiness of the structure that the bad corner did not sag more than an inch or so. One other corner has some relatively minor damage from woodpeckers and so on, and some restoration of floors and internal timbers that were cut by impatient workmen in the past will be necessary. I do not think the barn was ever painted, so I am wondering exactly what to do with the siding.
The main first questions were how much of the bad corner timber to replace to stabilize the structure and to do it using correct timber-framing practice so as not to destroy the historical integrity. It is difficult to take out a corner post, because girts and such are mortised in from both directions. Many tenons have to be cut if you want to take out the corner timber, or else you need to basically dismantle the whole thing. As you can see, I chose to replace the bottom portion and the top portion, leaving the solid center section that contains many of the mortises. The tenons were already bad in this lower section, although one critical one had only a bad relish, so all I had to do was trim them back. I obtained some 12inx12inx10ft white pine timbers, which match the originals, for the replacements. Jacks and braces were used on both levels to take the load and raise the roof about 2 inches beyond plumb to give some working room. As you can see, the bottom section is morticed and ready to be swung into place. I decided to let in keys top and bottom of the repair section rather than use mortise and tenon, given the space available and the tricky fitting to the existing mortised beams and braces. I will need to use a couple of irons or else let in some pieces to firm up the components that were held in place by the bad tenons. Load bearing will be okay, as the beam ends are solid and will rest on the mortise shoulders as in the original.
I will add some more pictures and details as time goes on. This is slow work and time is limited. If I do it right, this barn should last another hundred or so, unless some developer gets his hands on the farm and thinks a golf course or condo is more valuable than a fine old timber-frame barn.
By the way: any good ideas for evicting the bats that moved in a couple of years ago. Bats are great, in their place, but they do make a mess. Do not suggest that I plug all the holes. That cannot be done with a barn of this type, and the airy nature of it has probably kept it dry and safe.