TopCap
InstallationFor 0°, 45°, and 90° — same steps
Welcome to GAPCAP™ — your solution for enhancing the appearance of your deck by seamlessly covering corner gaps. Here's how to install your TopCap on a new build, before the deck boards are locked down. The steps below work for every TopCap angle: 0°, 45°, and 90°.
Measure and mark
Use your speed square to align and identify the exact position where the TopCap will sit. Ensure the cap lines up with the outer corner of the deck — same approach whether you're working a 0° end cap, a 45° miter, or a 90° outside corner.
Mark the width of the underside of the TopCap onto the deck framing. Your deck boards will be cut exactly 3/16" away from the underside of the TopCap to allow for seasonal expansion and contraction.
Install the deck boards
Install the deck boards in a picture-frame style, per the manufacturer's instructions. Maintain a 3/16" space between the deck-board miter and the underside of the TopCap on every corner.
Install the GAPCAP™ TopCap
- Insert the TopCap into the groove, ensuring it aligns perfectly with the corners of the deck boards.
- Secure the TopCap using composite deck fasteners — correct size, color-matched to the cap.
- Use a drill to drive the screws below the TopCap surface so the plugs sit flush.
- Install the provided plugs and orient to match the grain. See plug guide →
Final checks
Inspect the installation to confirm there is enough room for the deck boards to expand and contract with changes in weather. Confirm the TopCap is securely fastened and sits flush with the surrounding deck surface.
By following these detailed steps, you can effectively install a GAPCAP™ TopCap on your new deck — covering unwanted gaps and ensuring a neat, professional finish.
Pro tips for a flagship-quality install
- Dry-fit the TopCap before fastening any picture-frame boards. It's easier to adjust a deck board than a cap.
- For composite decking, the 3/16" gap is non-negotiable in cold weather. Skipping it is the #1 reason caps buckle in summer.
- Drive screws perpendicular to the cap's underside channel — angled fasteners can chew the channel and leave plug-seating problems.
- Mix-and-match colors intentionally: a black TopCap on brown decking reads as a designed accent, not a mistake.