Diagonal Composite Decking Installation: Step-by-Step Guide

Installing composite decking boards diagonally is an excellent way to elevate your outdoor design. A diagonal or angled layout adds visual depth and can make smaller spaces feel larger and more dynamic.

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Thu, 28 Jul 2026

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This step-by-step guide explains how to install composite decking boards diagonally, ensuring a durable finish that lasts for decades.

How to Install Composite Decking Diagonally

  • Recommended joist centres for diagonal installation are 250mm.

  • It is also recommended that you add 15% extra material when building a diagonal deck as you will generate more scrap from cutting.

Step 1 - Install the central board

Place the central board first; ensuring to place the board at a 45° angle.

  • Install 1 hidden fastener each time the board crosses a joist.

  • Always use hidden fasteners to secure board ends.

  • Use 1 fastener per board end at butt joints (never share a fastener across 2 board ends).

  • Use a mitre square to ensure an exact 45° angle.

Step 2 - Install the remaining deck boards

After laying the central board, progressively place each board outward toward the subframe corners.

  • Boards offcuts can be kept and used for finishing the corners.

  • Allow a slight overhang over the edge of the substructure.

Step 3 - Trim and finish

Once all boards have been fixed in placed, trim the deck board overhang with a circular saw.

  • Complete the deck with an edge finishing.

Key Installation Tips

  • Allow for extra material, diagonal decks use more boards due to angled cuts.

  • Tighten fixings evenly to prevent board lift at corners.

  • Check alignment frequently, small errors compound over distance.

  • Use hidden fasteners for a clean, uninterrupted surface.

Modern Style Meets Lasting Performance

Installing composite decking diagonally creates a sophisticated, high-end finish that enhances the visual character of any outdoor space. With planning, proper support and accurate cutting, a diagonal layout provides exceptional strength and timeless appeal.

Whether you’re designing a feature deck for a garden, balcony or commercial terrace, composite decking offers the stability, colour consistency and durability needed to achieve the perfect angled deck installation.

EnviroBuild offers a complete range of composite decking boards, hidden fasteners and substructure systems engineered for modern installations.