How to build a basic square pergola

Design details

Pressure-treated posts, though ideal for durability (especially below grade), inevitably crack, or “check.” While checking does not affect strength, it can be unsightly when the wood is painted.

Capping the posts with boards more suitable for painting, such as better grades of pine or redwood, gives this structure the benefits of both types of wood.

In addition, the fascia provides a ledge for the 2-by-8 beams, effectively eliminating the need for bolted connections.

The architectural details at the ends of the front and rear beams can be adapted to blend with design elements of your home or garden. Before cutting the beams, experiment with shaped plywood patterns tacked onto the ends of uncut 2-bys.

Building notes

Cut the posts in place after erecting them. Lay out the positions of the crossing 2-by-4 trellis pieces, and then mark the tops of the lower ones for the overlapping pieces.

Cut the fascia boards so they will end a couple of inches above a concrete patio and even more above soil or plants. After cutting the posts’ 1-by-8 fascia boards, soak the ends in a wood preservative to protect the end grain from moisture damage.

To install the two side beams, tack cleats onto posts 7¼ inches down from the top.

Cut the notches in the trellis 2 by 4s with a jigsaw, using the first board as a template for the others; or, clamp the 2 by 4s side by side for gang cutting with a circular saw.

Prime all the cut lumber before installing it. Use a drum sander or sanding attachment to smooth the end grain of the ogee cuts on the long beams. Countersink all nails, and then fill the holes with exterior filler prior to applying the finish coat. 

More: Backyard arbor and trellis projects