Prior to my last post, my thoughts were going to the design and building of the timber frame barn and some of its fundamental elements that are now an essential part of how I design and build my furniture today.
When I designed and built the timber framed barn that is now my shop, I used as my foundation what I’ve learned about the beneficial characteristics of wood and what conditions a design should have to allow it to perform at its best. Those are, as mentioned in previous posts, the ability to move and breathe. In that sense, the wood is “alive” still and can remain so for a very long time - provided it can move and breathe.
It’s arguable within the evolution of building with wood who can lay claim to timber framing techniques, but the Scandinavians certainly rank high amongst them. I called my build “traditional Norwegian” because this was the source for a lot of the information I used. However, if you think about it, deciding the origins of building with wood…or anything for that matter…is a bit like trying to assign who gets credit for harnessing fire. In evolutionary terms, shelter happens, and we learn by experience, so what ultimately didn’t work so well before is selected out next time so we get better results, and through that process our understanding of why wood works and how to enable it to do its work developed.
OK, enough proselytizing, now on to what I did with my beliefs.
The entire timber frame was raised using only wood. No metal fasteners or brackets of any sort were used. That means no nails, screws or any other such thing. Only wood. Where necessary, the joinery was pegged or wedged using various hardwoods based on their properties, e.g. Ash was used for pegs because it is flexible, Red Oak was used for wedging because of its compressive resistance. The frame timbers themselves were green Eastern White Pine felled and sawn only a month before starting the construction. First question many ask is why green? The answer is that the wood works easier when green plus the timbers are sawn nice and straight, which would change a lot if left to air dry first, then they would have to be sawn and planed all over again.
Also, when you build green, you lock the timbers into shapes that they will retain as they slowly dry over time. Some checking and movement can happen, but when the whole structure is locked together with joinery it’s a bit like having it in traction, and it stays true to the form. Likewise the tenons and other joinery involved remain supple as it dries, and any movement from environmental influences are “memorized” in the wood fibers so that a standard deviation of movement can occur with future swings in temperature and humidity.
When putting these joints together, I heavily waxed the mortises and tenons with a concoction of tung oil, linseed oil, bees wax, pine rosin, and citrus solvent. This is to help slow the drying process more to give the wood fibers more time to adjust to their new roles. Think of bending a toothpick. If you bend it very quickly it's liable to snap whereas if you take your time and bend it slowly you can bend it a lot more without breaking it. The company I bought the oils from, Heritage, has a nice article about how this helps the timber frame with its seasoning, and I highly recommend their products. The entire frame, after raised, also received a coat of a much thinner version of this. I also treated the sheathing this way. This is more of a deep saturation protective measure that still allows the wood it’s movement and breathing freedom.
All of the joinery was cut on the ground, and since it’s prohibitively heavy, trial fitting is not practical so I created sample joint parts to carry around like templates for trial fitting.
Here are some pics of joinery that I'll explain more about below:
I mentioned the use of wood on wood with different characteristics that would allow for movement. This is a key feature. For dovetailed joints I over-sized the mortises about 3/16ths of an inch to allow room for a 3/8ths inch wedge to be driven in on both sides. This had the effect of both drawing the joint incredibly tight and compressing the pine just a bit so that when ultimate drying is realized there is not much loosening. However, all members being wood, movement is also allowed. For scarf joints which I used along the 40 ft. continuous top plates, I temporarily wedged them with pine so as not to restrict them too much when raising. I felt that there was enough chance for timbers of that length to flex during raising, and didn’t want to restrict that joint too much until after it was raised at which point I drove the pine wedges out and replaced them with permanent red oak wedges. Necessary? I don’t know, it was a personal call, but didn’t seem to hurt. Ash pegs were used in the other direction to hold these joints longitudinally. Tapered Ash pegs were also used for all other tenon type joints because they are strong, yet Ash stays somewhat flexible so again, when movement occurs it’s less likely to split out the tenon ends. Additionally I used a "draw-bore" technique where the bores for the mortise and tenon were offset 1/8 inch from each other so that when the peg was set it drew the joint tighter to the point of slightly compressing the pine. Again, this helps keep things tight as the wood ultimately dries fully. One of my favorite joints is the half wedged dovetail which I used in places where tension was likely to occur (the same with dovetails). These are tenons that are wedged on one side, and the mortise is cut with the same shape but about 1 ½ inches wider (the width of the wider side of the taper) to allow the joint to go together. After it drops into place, a 2” Red Oak wedge is knocked into place forever locking it down.
I have to inject here that my ultimate favorite joint in the whole structure was the English Tying Joint. This elegant joint works like a Chinese locking puzzle and was used for the junction of the primary posts, top plates, and tie beams. One tenon locks into the bottom of the top plate, another at 90° locks in the bottom of the tie beam, and then a dovetail mortise is cut into the top of the top plate to receive the end of the truss. When done and in place it provides stability and strength in all directions.
When the frame was raised and complete, it’s structural integrity is “Ipso facto" per se, or in and of itself. What I mean by this ridiculously redundant statement is that the timbers are in a state of compression or tension with one another (mostly compression), and not reliant on any other means of support. In days gone by, it was not uncommon for these structures to be moved as a single unit when river banks overflowed and other reasons. It’s hard to believe that people…whole communities…did this before the age modern machinery, but they did!
Just a bit more on the beauty of using wood alone vs. with metal hardware. As I’ve mentioned all along, the wood has to move. In a contest between wood fibers and steel, the steel will win every time. The result is that the wood fibers fail, and the integrity of the wood’s strength is compromised. But there’s also another element. Breathability and moisture control. Not only does the metal create a vapor barrier that impedes drying, but also creates moisture through condensation. Metal, stone, and similar things “sweat” with the changes in humidity and temperature so moisture clings to them where it sits against the wood where it can’t escape, and becomes a breeding ground for wood destroying fungus.
OK, well if you stayed with me this far, I have to assume you were interested or incredibly bored, but I hope you enjoyed reading. If you'd like to see more pictures of building the barn to its completion, you can see the timber frame construction link in the workshop page under "about".
As always, your comments are welcome, and thanks for reading!