Proper Installation for Capped-Composite Decking

Manufactured decking brands like TimberTech have redefined the reliability and versatility of modern decking. From impressive durability to low-maintenance care, manufactured materials offer a wide range of benefits. But to get the most out of innovative products like TimberTech decking, it’s important to move beyond surface-level features and understand the nuances of each material—and the best practices for working with them.

In our TimberTech series, we're joined by Pat Maher, product application manager and head of AZEK University (TimberTech is an outdoor living brand of the AZEK Company). TimberTech is an industry leader in manufactured decking and a longtime Dunn Lumber partner. Pat brings a lifetime of experience in building materials, with 20 years focused specifically on manufactured decking. We’re excited to share his unique and seasoned perspective.

In this episode, Pat details installation best practices for capped-composite decking. While PVC and capped-composite decking are both manufactured materials, they behave differently. Follow this guide to achieve the best-looking finished product.

Like PVC, covered in another episode, capped-composite decking expands and contracts with changes in ambient temperature. One key difference: Composite boards don’t stop expanding once they meet resistance. Made of dense wood-flour material, composite exerts more force as it expands—pushing harder against adjacent boards or structures like posts or exterior walls. This pressure can cause boards to flare, lift, or even displace structures.

To avoid these issues, adequate spacing must be incorporated between butt and miter joints. Later in this post, we’ll cover the TimberTech fastening system recommended for establishing proper gap size. Always reference the TimberTech installation guide to determine the correct spacing based on ambient temperature at time of install.

Leaving enough spacing is not only important for expansion and contraction, but it also allows for proper airflow and drainage—two components that are necessary for maintaining composite material. With the proper amount of spacing, deck boards can aerate, and water and debris can drain off the surface.

To avoid spacing issues, you can consider eliminating butt joints altogether using divider boards. Divider boards run perpendicular to the main decking boards, creating a clean transition point for the ends of each board to meet. Picture framing is another effective technique. By using a double or triple picture framing border, you can shrink the infield of the deck to the length of a single board and therefore avoid managing butt joints.

For capped-composite decking, you can fasten boards by driving screws through the face of the board into the joist. The Cortex Hidden Fastening System countersinks the screw and covers it with a color-matched plug for a clean finish.

When fastening the ends of capped-composite boards, position the fastener ¾” from the board’s edge and drive it perpendicular. In some cases, two boards may meet in a butt joint over a single joist—but due to the spacing needed, the screw may not align with the joist. While some may try “toenailing” (angling the screw to catch the joist), this can easily crack the board ends and isn’t recommended. Instead, sister a support block to the joist to allow proper, perpendicular fastening.

There are two key considerations when fastening capped-composite boards:

1. Always pre-drill using the correct diameter bit. Even if screws are labeled “self-drilling,” composite is so dense that driving screws without pre-drilling will push the material out, creating internal pressure that can cause the boards to split. Pre-drilling removes excess material, relieving pressure and preserving the board's integrity.

2. Insert plugs immediately. After setting the countersunk screw, place the color-matched plug right away—before moisture (like rain or dew) enters the hole. Composite’s wood-flour core absorbs moisture, which causes swelling and shrinkage that can reintroduce pressure and lead to cracking when fastened.

CONCEALoc^® Hidden Fasteners are another option for TimberTech composite decking. These metal clips attach to the grooves of the board and secure it to the joist. Unlike ordinary clips that simply pinch the board, CONCEALoc prongs bite into the composite for a stronger hold.

Following these best practices—and thoroughly reading your installation manual—is the best way to achieve a high-performing, long-lasting outdoor space.

If you have questions, TimberTech’s customer service team is ready to assist with your installation.

Join us next time as Pat discusses the importance of leveling your deck framing before installation. In the meantime, explore our past series, including the Decking Series, Wood Technology Series, and Cabinet Series.