Trex Grooved vs. Square Composite Decking: What’s the Difference?

When designing your dream deck, you’ll encounter a choice between grooved and square composite decking boards. Understanding the differences between these two types of boards will help you decide which one best suits your project, whether you’re focused on aesthetics, functionality, or ease of installation.

In this post, I’ll explain the benefits of Trex grooved and square decking and how they differ, and share some insights I’ve picked up over the years from building and working with these materials. With the guidance here, you’ll be prepared to choose the best option for your new deck.

Trex Grooved vs Square Composite Decking

Grooved and square composite boards are designed to offer homeowners versatile decking options, but they do serve different purposes. The main difference between the two is how they attach to your deck’s frame and how seamless the final look appears.

• Trex Grooved Boards: These feature a notch or channel along the sides, specifically designed for hidden fasteners. This creates a sleek surface without visible screws, ideal for those who prioritize a clean, contemporary finish.

Pro Tip: When using this style, I recommend finishing off your deck edges by covering the grooved ends with picture-framing or fascia boards.

• Trex Square Boards: Also known as ungrooved composite decking, these square boards have the profile of typical timber boards. They lack side grooves to accommodate hidden clips for fastening and are usually attached with surface screws instead.

Pro Tip: Although not completely hidden, colour-matched screws or plugs can help make your surface screws far less noticeable.

When I talk with homeowners considering a composite deck, we always discuss these two board options upfront so they can decide whether the hidden fasteners or more traditional surface screw-down method better suits their aesthetic and—if they’re installing their deck themselves—their DIY comfort level. By understanding each type of board, you can better design your deck to meet your expectations in terms of appearance and installation. So, let’s dig into grooved and square composite decking!

Trex Grooved Decking

Grooved Trex deck boards are ideal for creating a clean, fastener-free surface. They offer a sleek look for your deck, designed for use with hidden clips that securely attach to the joists underneath.

When to Use Grooved Boards

Grooved boards are an excellent choice if:

• A seamless surface is a priority: Achieve a polished look without exposed fasteners.
• Comfort underfoot is essential: Enjoy a smooth, barefoot-friendly surface.
• Your deck is large: Hidden fasteners create a sleek appearance, especially over large areas, by eliminating the visual clutter of many screw sites.

Grooved boards are perfect for outdoor spaces where you desire a clean, modern look. Homeowners I work with love how they create an uninterrupted surface that feels like a natural extension of their homes.

How to Install a Grooved Board

Installing grooved boards requires a hidden fastener system like Trex’s Universal Fasteners. Here’s the simplified process:

1. Construct the frame: Build your deck frame according to local building codes, ensuring proper joist spacing.
2. Insert clips: Snap hidden clips into the grooves on the side of each deck board. These clips hold the board in place and will be used to secure the board.
3. Secure with screws: Drive screws through the clips into the joists. This will lock the board in place.
4. Position the next board: Slide the next board into position over the clips, or use board benders to hold several boards and their clips in place simultaneously so you can fasten them in batches.

This method eliminates the need for visible screws on the deck’s surface, giving your outdoor space a streamlined appearance.

Square Composite Decking

Square composite boards offer a classic, traditional wood decking look and are a good option when completely hidden fasteners aren’t required. Their simple, face-screwed installation makes them a popular choice among DIY homeowners.

When to Use Square Boards?

Square-edge boards are your best bet if:

• Edges will be visible: The solid ends of square boards offer a cleaner appearance than grooved ends when exposed, making them ideal for simple or traditional deck designs without decorative edge boards or fascia.
• (Somewhat) visible screws aren’t an issue: While visible screws are a drawback for some, they can offer a rustic or traditional appearance, similar to classic wood decking. For a subtler appearance, you can opt for colour-matched screws that blend with your deck boards. The most popular option with my deck owners is a plug system that hides the screws with plugs made from the decking material: The matching grain patterns create a nearly seamless finish.

• Pro Tip: Solid boards can be edge-fastened to avoid face screws. I find this method more challenging and prone to splitting, requiring precise pre-drilling and alignment. Unless there’s a specific design reason, I choose grooved composite boards for a fastener-free surface.
• Grooved board edges need to be covered: Use square boards to create a picture frame around the edges of your grooved decking. This technique hides the less-attractive grooved ends and maintains a clean, finished look when you use plugs to cover the screw heads.
• Cost is a major factor: Trex square boards may be more budget-friendly because they’re installed with standard screws instead of a clip system. This can lower both material costs and make them a DIY-friendly choice for budget-conscious deck projects.

Whether you’re interested in a traditional look, managing costs, or seeking an efficient way to finish grooved edges, square boards provide a straightforward solution that adapts to the needs of your outdoor space.

How to Install a Square Board?

Installing square composite deck boards is a simple process that many DIYers feel confident tackling themselves:

1. Construct the frame: Build your deck frame according to local building codes, ensuring proper joist spacing.
2. Pre-drill: Trex composites are durable. However, I recommend pre-drilling your screw holes to avoid any splitting.  If you plan on using plugs, be sure to use a specialized bit or plug cutter to drill both the pilot hole and create a recess for the plug in one go.
3. Use deck screws: Insert deck screws directly into the board, securing them to the joists below.
4. Position screws: Place screws about 25 mm from the board edge and approximately 30 cm apart along the length of each board, aligning them with the joists below.

While this method involves face screws on your deck surface, it’s a strong, traditional installation that homeowners familiar with timber decking may prefer—and you can always elect to camouflage the surface screws if you like.

Which Should You Choose?

So, which Trex decking board is best for your project—grooved or square? The answer depends on your priorities for the decking design.

• Choose Trex grooved composite decking if you want a seamless look without visible screws, and you’re comfortable installing a hidden clip system (or are planning on hiring a professional contractor). This option is particularly suited for barefoot-friendly decks and larger spaces where a streamlined appearance enhances the visual flow.
• Opt for Trex square composite decking if you prefer a more traditional approach or need them for specific design elements like picture framing. Square boards offer versatility and can be a great choice for DIYers who don’t mind surface fasteners.

Both Trex grooved and square boards offer outstanding durability, low maintenance, and eco-friendliness. Whether you’re building a new deck or upgrading an old one, you can feel confident knowing you’re selecting decking that will stand the test of time. Consider both options as you plan your deck and create a beautiful, functional space you’ll enjoy for years to come.