Decorative joint for exterior pergola with pressure treated lumber

borderguy · Aug 9, 2017

Building a deck pergola and need to join two 2" X 12" X 12' to cover a span of 24' with columns to support the span. I don't know what kind of joint to use for this application. The joint will be very conspicuous on the front of the house so I am trying to turn it into a feature. Would a finger or dovetail joint be appropriate for this application? What joint will provide enough movement to not weaken the structure over time? The project is similar to this picture.

Toolman50 · Aug 9, 2017

I don't think finger joints or dovetails would be your best choice with two 12' boards. I would probably use a lap joint. If you want to hide the seam you could add a short 3rd board made to look like a key at the top of an arch. This would hide the center seam and could add more strength to the joint.

woodnthings · Aug 9, 2017

woodworking joints won't work in this case

This is a construction/framing project and woodworking joints aren't usually used for this. In addition, unless one of the cross members is directly over the seam, or centered there's no need for a lot of structure in the joint. A simple 3/4" x 12" X 2 ft block on the back side that won't show will provide all the structure you'll need. :smile3:

Decorative joint for exterior pergola with pressure treated lumber

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