Timbers don't shrink much in length, So most of the critical measures stay close to original. Using shouldered joinery will help conceal shrinkage at the joints. End grain sealing will slow down shrinkage and the damage it can cause. Make blind mortices at least 1/4" deeper than the tenon. Watch out for wide joists, a 6" joist pocket will show plenty of airspace down the road(maybe better to reduce the joist ends a bit?). If you can go look at some old barns, you'll get a first hand lesson in the problems of shrinkage. Most farmers I know are happy if someone wants to look at the old barn.....(provided the old barn is still standing, many are being torn down)
