Sheathing was the skin between the frame and the world. Boards nailed diagonal across the studs to brace the wall and seal the cavity. The sheathing turned a skeleton into a body. Without sheathing the studs were ribs you could see through. With sheathing the wall was a wall. The sheathing was the moment the building stopped being an idea and started being a building.

The boards went on diagonal because diagonal resists racking. A square wall wants to become a parallelogram when the wind pushes it. The diagonal board turns the square into triangles and a triangle cannot rack. The triangle is the only shape that cannot be pushed out of true. The carpenter knew this. The carpenter did not say triangle. The carpenter said let-in brace. The carpenter said diagonal sheathing. The math was in the nails.

Sheathing was rough. It was not finish lumber. It was not sanded. It was not planed smooth. The sheathing did not need to be beautiful because the sheathing was never seen. The siding covered it from outside. The plaster covered it from inside. The sheathing lived its whole life between two surfaces that got all the attention. The sheathing was the middle child of the wall. The middle child holds the family together and nobody puts the middle child in the photograph.

They replaced the boards with plywood. The plywood was faster. One four-by-eight sheet covered thirty-two square feet in one nail pattern. The boards covered thirty-two square feet one board at a time. The plywood was efficient. The boards were thorough. Efficient and thorough are not the same thing. Efficient means you covered the wall. Thorough means you understood the wall. The carpenter who nailed each board understood which way the grain ran and which way the wind blew and put the grain against the wind.

OSB replaced the plywood. Oriented strand board. Wood chips glued into a sheet. The tree is no longer a board. The tree is confetti pressed into the shape of a board. The confetti holds the house up and the house does not know the difference but the carpenter knows. The carpenter picks up OSB and picks up a board and the board has weight that means something. The OSB has weight that means glue. There is a difference between wood and the memory of wood.

See also: Stucco, Clapboard