How can one person make a building that will endure for centuries when another's work falls and turns to compost long before he does? Take some time to study the skeleton of a well-framed old barn. (It must have been well-framed. It's still standing, isn't it?) You will see the truth of what a 1745 book of trades said of the carpenter, that "Strength is the chief of his study."
Study the barn's frame, its vertical posts, horizontal beams, and diagonal braces. Older than Stone- henge, this "post-and-beam" construction is the essence of the English building tradition. Indeed, the first English settlers in the New World built houses and barns that were not much different from the ancient stone monuments they had left behind: simple frames consisting of posts set into the ground with beams spanning their tops. They were wooden houses, but hardly the work of carpenters. It's no wonder there aren't any of them left.
If you think of a building as a human body, then the old-time carpenter's job is to make the bones and the skeleton—the strong frame to which the joiners and roofers later apply the protective skin. Good carpentry makes strong frames by exploiting the wood's strength in three dimensions: the size of the building's individual timbers, the connections between these pieces, and the design of the frame as a whole. When all these aspects of the building work together, the carpenter has earned his pay.
Take a wooden pencil and push in from its ends to make it shorter. No go. Now bend it and it snaps in half. The point is that it is easy to make a strong post but harder to make a strong, yet lightweight beam. You need a way to size timbers so that they are as strong as they need to be, but no heavier than they must be. Fortunately you can turn to a simple guideline for help: The strength of a rectangular beam varies directly with changes in width. With changes in depth, however, the difference in strength is squared.
Imagine that you have to support a load with a beam measuring 2 inches wide and 4 inches deep. A 4 by 4 would be twice as heavy and twice as strong. A 2 by 8, however, twice as deep as the original timber, would also be twice as heavy, but would have four times the strength. A 2 by 12 would be nine times as strong, and only three times as heavy. The more a carpenter knows about the strength of his timbers, the more confidently he can approach the limits of the material.
You often hear that old buildings are held together entirely by wooden pegs. True, the pegs are there, but the strength of the buildings is not in their pegs, but in their joints. These mortise-and-tenon joints interlock the timbers so that they sit solidly within one another. It is a rare building from which you couldn't remove every peg and have it stand as strong as before. (Try this with the nails in a modern structure.)
Although a post planted deeply in the ground won't fall over, it will invite destruction by termites and rot. Once you protect a building by placing it up on foundations, however, you must stiffen it by adding the strength of triangles to the rectangular frame.
Diagonal braces strengthen the building in several ways. Ideally, a post is a perfectly vertical column that is compressed but not bent. If the post does start to bow, it can snap relatively easily. Braces connected to the post prevent the bend from getting started. And, by blocking the closure of the right angles created between posts and beams, braces also prevent the collapse of a building under wind.
The old hand ways,
The old hand ways - THE CARPENTER,
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