It is very important to follow the manufacturer’s instructions when installing composite decking material. Thermal expansion is always something to be aware of when dealing with plastics. In most climates, temperatures fluctuate enough to cause an issue with how the decking is spaced from summer to winter. Composite decking tends to grow and shrink across the length of the boards as it heats and cools. Proper spacing will allow some movement without buckling.

Some composite decking materials are designed to be installed with hidden fasteners. These clip systems generally are screwed into to the deck frame across each joist and fit tightly into a cavity running down the side of the boards. 

We recommend using reverse thread screws when face-screwing composite decking to eliminate mushrooming. Mushrooming occurs when a standard bugle head screw pulls some composite material above the surface during installation. The resulting raised bump isn’t very attractive. You can also use a hammer to level the surface.

Hollow decking products will leave open ends that aren’t attractive and can collect dirt, leaves, etc. Most hollow decking products sell end caps that can close the ends. Another method involves installing a racetrack or picture frame pattern perimeter to cover the open ends. 

Controlling Deck Seams

It is always best to try to avoid seams on your deck surface. Butt joints tend to separate and warp as the decking material weathers. Depending on the size and shape of your deck design, this may be easy to accomplish without any effort, or you may have to make some adjustments. Applying decking diagonally can often reduce or eliminate the number of butt joists on decks that are over 20’ wide. In some cases, you may decide that it easier to use a division board to create one continuous seam across the deck surface. This technique is used to control the seam and make it appear to be a part of the design.

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Notice the blocking on the sides to support the border.

The field deck in this picture is 24' wide with an additional 6" picture frame border. In this case, we are staggering the butt joints every 4'. We added double 2x10 joists to support the seams. An alternative is to use a division board and create 2 decking fields.

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Leveling the double joists.

Make sure you level both joists to the same height and fasten with 4 screws every 12" to support the composite butt joints.

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Grooved decking with hidden fasteners.

Leveling the joists is very important to keep the butt joints at the same height. Be sure to use 2 clips on the double joist when using a hidden fasting system. Make sure to gap the butt joint at least 1/8".

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Line up the seams over double joists.

To install composite decking with a hidden fastening system, start at the house by face-screwing the first board. Next, screw a hidden fastener clip into the groove on top of each joist. Then, slide the groove of the next board into the clips and tighten with a rubber mallet.

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A clean looking deck border.

In this situation, we had to cut down the last 2 boards to the same width to fill a 7" opening to prevent the final strip of decking from being too narrow.

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Decking around an inside rail post.

Notch your composite decking material around rail posts. Make sure to leave at least an 1/8" gap for thermal expansion. In this case, we will be using a rail sleeve and base trim that will cover the gaps.