Trex Deck Board Spacing

Creating a beautiful and long-lasting deck requires not just quality materials but also attention to detail in the installation process. A critical aspect of deck building is the proper spacing of deck boards, particularly when using popular materials like Trex composite decking. This post will delve into the recommended gap spacing for Trex deck boards and explain why this aspect is crucial for your deck’s longevity and aesthetics.

Trex composite decking is designed to expand and contract with temperature changes. To accommodate this natural movement and ensure the longevity of your deck, precise spacing between the boards is necessary. The recommended gap spacing for Trex deck boards is:

  • 1/4″ to 3/8″ (6mm to 10mm): This gap size is ideal for most Trex decking applications. It allows sufficient space for the boards to expand and contract while maintaining a uniform appearance.
  • 3/16″ (5mm) Around Perimeter and Objects: Near fixed objects or the deck’s perimeter, a slightly smaller gap is advisable. This size helps in temperature-driven expansion and contraction, preventing the boards from pushing against the fixed structures.

Why Proper Spacing is Important

  1. Thermal Expansion and Contraction: Composite materials like Trex expand in warm temperatures and contract in colder ones. Without the right spacing, boards can warp, bulge, or even crack due to the stress caused by temperature changes.
  2. Drainage and Drying: Proper spacing allows water to drain off the deck surface easily, reducing the risk of water damage, mold, and mildew growth. This is particularly crucial in areas that experience frequent rain or snow.
  3. Aesthetic Consistency: Even spacing contributes to the overall visual appeal of the deck. Uniform gaps ensure a clean, professional look that enhances your outdoor space’s beauty.
  4. Preventing Debris Buildup: Small debris like leaves, twigs, and dirt can get trapped between deck boards. Adequate spacing helps to minimize this buildup, making your deck easier to maintain.
  5. Ensuring Structural Integrity: Correct spacing helps distribute weight evenly across the deck, reducing the risk of boards bending or breaking under pressure.

Tips for Proper Installation

Use Spacing Tools: There are tools designed specifically for decking installation that can help maintain consistent spacing between boards. We recommend the DeckWise deck board spacers to help ensure your deck boards are properly and evenly spaced.

DeckWise deck board spacers

Account for Temperature: Install your Trex decking at the temperature closest to your average yearly outdoor temperature. This helps in predicting the expansion and contraction behavior of the boards.

Follow Manufacturer Guidelines: Always refer to the installation guide provided by Trex. They offer detailed instructions and tips for proper installation.

Consider Professional Help: If you’re unsure about tackling a decking project on your own, consider hiring a professional. They have the expertise to ensure that the deck is installed correctly.

Additional Trex Gapping Specifications:

Gapping and Overhang

You must gap Trex decking both end-to-end and width-to-width. Gapping is necessary for drainage and the slight thermal expansion and contraction of Trex decking boards. Gapping also allows for shrinkage of the wood joist system.

  • Maximum allowable perpendicular overhang for all Trex decking is 1/2″ (13 mm).
  • All decks require air circulation to keep them dry and looking good. To improve air flow, leave openings under the decking or increase gapping to 3/8″ (10 mm).


The minimum required width-to-width gapping is 3/16″ (5 mm). This is allowed for both hot and cold weather installations. For docks and heavily wooded areas, Trex recommends a 3/8″ (10 mm) gap. No gapping should ever exceed 1/2″ (13 mm).

Temperature at Installation:

Above 40°F (4.5°C):

End-to-End/End-to-Width: 1/8″ (3 mm)

Abutting Gap: 1/4″ (6 mm)

Below 40°F (4.5°C):

End-to-End/End-to-Width: 3/16″ (5 mm)

Abutting Gap: 1/2″ (13 mm)

Trex Hidden Fasteners

When you use the recommended hidden fasteners,the placement of the hidden fastener establishes the designated gap size.

In conclusion, paying close attention to the gap spacing between your Trex deck boards is a crucial step in ensuring a durable, beautiful, and safe outdoor living space. By following these guidelines, you can enjoy your Trex deck for many years to come. Remember, a well-installed deck not only adds value to your home but also creates a perfect space for relaxation and entertainment.

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