Rabbet PVC Fascia Seams So Expansion Stays Hidden

The Problem

PVC fascia moves. Through a season's temperature swings the boards expand and contract along their length, and there's no fastening schedule that stops it. Butt two boards square against each other and the seam telegraphs every move — tight in summer, an open gap in winter, right at eye level on the face of the deck.

The Technique

A deck crew's standard detail: instead of a square butt seam, cut a rabbet — a step — into the joint so one board overlaps the other. The boards still move exactly as much as they always would, but the movement happens inside the overlap. Whether the joint is at its tightest or its widest, what shows from the outside is a continuous face; the gap opens and closes behind it, hidden from view.

The video is worth a watch for the cut itself — the geometry of the step is easier seen than described.