Traditional Mortise and Tenon Joinery

The joints are one of the most important parts of an oak pergola. At Timber Solution, we use traditional mortise and tenon joinery for strong and durable timber connections. The tenon fits tightly into a matching mortise and can be 25–50 mm thick. Our tenons penetrate approximately 75 mm into the oak beam, creating a deep and secure connection. Smaller oak sections can work structurally, but they leave less room for strong traditional joinery. At corners, brace tenons may need to be shorter or two joints may come very close together. Less timber around the dowel hole can also increase the risk of splitting as the oak naturally moves and dries. Over time, moisture and winter conditions can make these splits worse. Using substantial oak sections gives our joints more depth, more timber around the connection and greater flexibility in the joinery design.

Why We Use Kiln-Dried Oak Dowels

We secure the joints with kiln-dried oak dowels instead of relying on glue or visible metal fixings. Green oak naturally loses moisture and shrinks as it dries. The kiln-dried dowel remains stable while the surrounding oak tightens around it. This creates a strong compression joint that becomes tighter over time. Some oak framers prefer stainless steel screws to attach braces to posts and eaves plates. At first, this seems secure. However, our yard tests show that as the oak dries and moves, metal fixings cannot adapt to timber shrinkage: Beams may twist or misalign, Gaps can appear around screw points, Joints may offset, affecting overall appearance.