I am posting a question here at the suggestion of Joel McCarty, whom I had originally pestered. A question about wood shrinkage. Working with dry lumber is a relatively recent innovation, I am told. Older timber frame houses and barns were built of green trees freshly chopped, because it is more workable. The wood shrinks but that's no problem with a medieval wattle-and-daub wall, since you just pack in more mud. Wattle-and-daub has gone out of fashion, however. Nowadays how do you compensate for shrinkage? Why don't tenons flex their pegs to the breaking point, and pull out of the mortises? How do windows stay shimmed? I understand with covered bridges the later 19th Century builders used iron tie bars, bolts, nuts and turnbuckles to keep the timbers tight--but the earlier ones didn't. In particular the beautifully symetrical Town truss which looks like a lattice, was all wooden pegs. And very tight. So I am curious about the strategies you've rediscovered of those experienced carpenters who were your forefathers, to cope with the certainty that a beam would shrink.

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)

To add to what Mark has mentioned. I believe it is a standard now amongst most timber framers to use a product called "Anchor Seal" (or similar product) on ALL end grain exposure, tenons, mortises, and etc... This helps to prevent end checking. I'm fairly new to timber framing, possibly someone else could provide more details on the benefits of what I've mentioned in relation to your shrinkage quetion.

Thanks for these helpful answers. I also found a great deal in the downloadable PDF files on this website written and illustrated by Jack A. Sobon called "Historic American Timber Joinery, a Graphic Guide." There is some interesting stuff about how tenons for the crucial tying beams (those in tension) were fashioned with dovetails and locked with wedges, to anticipate seasoning and shrinkage. One in particular called a 'kerf-wedged dovetail through mortise and tenon' in a building at the Hancock Shaker Village in Massachusettes has proven to be not up to the challenge. "Because of shrinkage of the height of the tenon, the wedges are loose, indicating the pins are carrying the load." Well I still like Shaker furniture even if their timber framing may not be an example to emulate.

One strategy we use in the scibeshops here in this part of NNE, is necessitated by the number of simple mortise and tenon joints scribe allows, which don’t allow the heavy dishing of housings. Instead we do the inverse, backcutting the shoulders ( 2-3 degrees ) along with light dishing around the mortise. Sounds awful, but isn’t an ascetic problem at all, I’ve never known a client to complain.

I would point out that the increasing amount of iron in later 19th century bridge patents was not in response to shrinkage problems but simply making use of a resource which was in ever greater supply while wood was less and less so. The engineers creating the patents were getting better and more formal training ( the transition to engineer as we understand it today was coming into being ) and learning the virtues of iron in that training. In addition. it is far simpler to deal with the massive loads the tensile webs convey with iron. Lastly it allowed for very simple carpentry, reducing labor costs.-
Most Towns have no shortage of bolts, and often iron wind stays.

Our challenge in dealing with shrinkage is greater now than it was for those we follow.
Simply in that it was not possible to condition a home as it is now and shrinkage is now accelerated. This hyper drying often causes the wood to distort to a greater degree than it might if allowed to season at a more natural rate –
All the same I choose to work green wood and consider timber framing green woodworking