How to Lay a Composite Deck

A no-nonsense DIY guide from Wood Green Timber

Composite decking — like Trex, which we stock in multiple colours and styles — gives you a clean, low-maintenance garden upgrade that’ll last for decades. It installs a bit differently to timber decking, but with the right gear and a solid plan, it’s a project confident DIYers can handle with no issues.

Here’s how to do it right.

What You’ll Need (From Us)

• Trex composite decking boards (grooved or square edge)

• Starter clips, hidden fasteners, or colour-matched screws

• Matching fascia boards

• Treated C24 joists (4x2 or 6x2)

• Weed membrane

• Optional: composite risers or support pads

Tools You’ll Need

• Drill/driver and impact driver

• Circular saw or mitre saw

• Tape measure

• Spirit level

• Square

• Pencil + string line

• Rubber mallet

• Spacers (Trex recommends 5mm)

Step 1: Plan Your Deck Layout

Start by measuring your space and deciding:

• Board direction

• Where your joists and noggins will go (spacing at 300mm centres for Trex)

• Whether you’re using a picture frame border or steps

• How you’ll finish the edges (fascia or face-fix border)

Top tip: Trex doesn’t offer L-shaped edge trims — so use square edge boards with colour-matched screws to picture frame the outer edge neatly.

Step 2: Build a Solid Subframe

Use C24 treated timber joists (4x2 or 6x2) on a level base:

• Paving slabs

• A concrete slab

• Composite risers or ground screws

Make sure:

• Joists are at 300mm centres

• The frame is square, flat and well-fixed

• There’s a slight fall (2mm per metre) for drainage

Step 3: Start Fixing the Boards

Grooved Boards + Hidden Fasteners (most popular)

• Start with starter clips on your first board

• Use hidden fasteners between each board

• Tap each board into place using a mallet and spacer

• Gives a clean, screw-free finish across the whole deck

Square Edge Boards + Face-Fixing

• Fix with colour-matched screws directly into the board face

• Ideal for borders, steps, or deck edges

• Pre-drill for the cleanest finish

Use fascia boards to trim the sides neatly and cover your joist ends.

Step 4: Work Across the Deck

• Maintain consistent gaps (5mm recommended)

• Stagger any joints for strength and a cleaner look

• Trim boards where needed and make sure cuts are clean and square

• Fix fascias and risers as you go — not as an afterthought

Step 5: Give It a Final Clean

Once all boards and fascias are fixed, give the deck a good sweep or hose down. No need for oiling or staining — Trex is good to go.

Why Composite (and Why Trex)?

• Made from 95% recycled materials

• No splinters, warping or rotting

• Never needs staining or sealing

• Available in modern colours with real grain textures

• 15 / 25 / 50 year guarantees depending on range

• Looks the part and lasts for decades

Need Help Planning Your Composite Deck?

We stock everything you need — and we’re always happy to help you figure out your quantities. Bring in a sketch, measurements, or just an idea, and we’ll talk it through.

Wood Green Timber — stockists of Trex composite decking, and your go-to for decking projects across North London & Hertfordshire.