Covering a wood deck with composite decking is a quick and easy way to get a new look. You will need to make certain that your frame will hold the additional weight by adding joists to make the spacing no more than 12 inches between framing members. Additionally, this technique should not be applied to decks with a frame that is older than five years because the added weight can pose a serious risk of collapsing the deck.
Reinforce your frame by adding enough joists to make the spacing between joists 12 inches or less. Most decks are framed with 16- or 24-inch spacing between joists. Use joist hangers to install your new framing members securely and easily. Attach them from underneath the deck if this is possible. If not, slide them under and into position and remove one or two deck boards along the outside rim joists to allow access from the top.
Square your joist hangers with the rim, or outside, joist and attach one side, folding the other side open to accept the joist. Attach the hangers at either end and measure between the outside joists.
Cut your new joist to length from the same size lumber as the existing joists and slide it into position underneath the deckl. Lift it up into the hanger and push the loose side of the hanger into position. Attach the loose side of the hanger to the rim joist. Attach the hanger to the new joist.
Attach the existing deck boards to the new joist with two screws in every intersection between them. Check the deck for additional problem areas. Add nails or screws to tack down any deck boards that are loose. Examine joints on posts and joist hangers and tighten any loose bolts or screws.
Begin at one corner of the deck to lay your boards. If your deck connects to the house, start along the outside edge. Lay your composite decking perpendicular to the original to prevent covering the gaps between boards entirely. This will allow precipitation and other moisture to run off. Screw the decking down with two screws side by side every 16 to 24 inches. Make sure to keep board rows straight. Use a quick square to keep them positioned 90 degrees from the existing wooden deck.
Use as many full lengths as possible to get the most out of your material. Measure and cut notches around deck posts and other obstructions carefully with a jigsaw. Cut them tight to start, you can always trim a little to get a good fit. Cut end pieces to length by attaching them to the deck and cutting off the overhang with a circular saw and a quick square. Use the cut-off piece to start your next row for an easy way to stagger the joints between board ends.
Butt-end joints between boards tightly and make your first set of screws within the first 4 inches of each new board for stability. Space between rows, using a framing square to allow proper drainage.
Drive screws until they are just below the face of the decking to prevent moisture build-up on screw heads, which can cause staining and deterioration of your fasteners. Use 1 5/8-inch, treated deck screws to make the attachment.
Trim the last board to fit along the house as snugly as possible. If it is running parallel to the house, use a chalk line to mark any bevel or angle it needs to make a good fit.
According to one manufacturer---see Trex.com for details---composite decking is more than twice as heavy and requires tighter joist spacing for safety. Be sure to add what you need to your frame.