An effective method of finishing a deck surface is to install a trim board around the perimeter of the deck. This technique is also called picture framing or racetrack decking. Some composite decking materials are hollow which can be concealed at the ends using this technique.
Blocking must be installed between joists where the picture frame boards will be parallel to the joists. Depending on the design of the deck perimeter, short deck boards may be required. When installing these, there are a few common installation practices to keep in mind. Generally, no composite board should be supported on less than three joists below. Where short pieces are needed to complete the frame, an additional support should be installed between the standard spacing. Minimizing the contact area between the decking and the support is also important.
Some deck builders install the trim board over the edge of the rim joist by about an inch in order to tuck the fascia board underneath. This allows water to drain off the board’s edge. This subtle detail can do a lot to improve the overall appearance of your deck.
Be sure to consider how your rail system will be attached and how your rail posts will intersect with surrounding decking.
Install blocking 1-1/2" below the top of the frame along the sides of the deck at least 16" on center. You may be able to use scrap material for blocking.
Install 2x4 material on top of the blocking around the perimeter of the deck for a fastening surface for the picture frame decking and to end fasten the field decking boards.
Install the picture frame border with the desired overhang. In this case it is 2-1/4" because of the skirting and fascia boards that will be installed outside the frame below.
Notch the picture frame border around rail posts. Leave a 1/8" - 1/4" gap for composite decking to allow for thermal expansion. Wood picture frame decking can be notched flush with the post.
You may choose to continue the picture frame along the house wall. Notice the 45 degree miter cut in the corner. In this case we needed to cut down the last 2 deck boards in the field to prevent the last board being only 3/4" wide.