Water and debris that collect behind the fascia board can eventually cause it to pull away from the deck. Here the fascia has rippled and deformed at its top edge.
On this deck, debris trapped behind a flush fascia held moisture, which led to rot in the decking and trim.
Where picture-frame decking runs parallel to the framing, blocking between joists provides support. Spacing the two outer joists 3 5/8 inches apart allows for easy installation of railing posts.
The innermost of the two outer joists supports the ends of the field decking. The inside edge of the picture-frame border should be just shy of the inner joist to allow drainage.
To support the fascia, blocking made from pairs of offcut 2x4s is installed approximately every 2 feet, and as needed to accommodate the shape of the deck. The longer leg of each 2x4 pair is fastened to the perimeter joist from behind so that the shorter leg aligns with the joist face.
Occasionally, the deck design or framing configuration requires the addition of horizontal blocking at the perimeter. In this case, the picture-frame decking border must extend far enough to cover the additional thickness.