Pergolas in Glendale, OH

Glendale (ZIP 45246) has houses from a period when carpenters joined timber with the timber itself, and a pergola made the same way sits naturally beside them. A traditional timber frame uses mortise and tenon joints held with wooden pegs, with no brackets or bolts showing anywhere on it.

The joint is the whole idea. The end of one member is cut down to a tongue, the tenon, which slides into a matching slot, the mortise, cut in the other. A hole is bored through both and a hardwood peg is driven home. In a drawbored joint the hole in the tenon is offset a fraction toward the shoulder, so driving the peg pulls the joint tight and keeps it tight as the timber moves over the years. Post to beam, beam to rafter and the angled braces at the corners are all made this way.

It wants larger timber than a bolted frame, because a mortise removes wood from the middle of a member exactly where it is joined. Posts are usually six or eight inches square, and beams are deep enough that the joint leaves generous section around it. The members are often oak or Douglas fir, and where they go up green they are cut knowing they will shrink across the grain as they season, which the offset in each peg hole is there to take up.

The joints are cut in the shop and the frame is trial fitted there, with every joint marked and numbered before it travels. On site it goes together in a day, raised in sections with the pegs driven and trimmed. Rain is the one thing a joint must never collect, so every tenon is sheltered by the member above it, mortises are kept out of upward faces, and each post stands on a raised stainless pin so no end grain sits in water.