You have made the investment in premium fencing, and now it is time to get it out of the boxes and into the ground.
The major advantage of our composite system is the weight. Unlike lugging around soaking-wet, unwieldy timber panels, our modular boards and rails are lightweight and designed to slide together seamlessly.
Whether you are dropping panels into existing concrete posts (which accounts for about 70% of UK gardens) or excavating a brand-new boundary line, this tradesman-approved guide will walk you through exactly how to build a fence that stays straight, secure, and structurally sound for decades.
Phase 1: The Golden Rules of Preparation
Before you even touch a circular saw, you must prep the materials. Rushing this phase is the fastest way to ruin a premium fence. If you haven’t yet ordered your materials, review our complete guide to panel styles, pricing, and kits to ensure you have the correct system for your specific garden layout.
The 48-Hour Acclimatisation
Wood-plastic composite (WPC) reacts to temperature. If you take a cold board out of a delivery truck and immediately lock it tightly into a sun-baked garden frame, it will warp as it rapidly expands.
- What you must do: Leave the boards outside in your garden for at least 48 hours prior to the build so they can adapt to the local climate.
- Pro-Storage Tip: Do not just leave them in a messy pile. Lay them completely flat. In the summer months, we highly recommend resting your boards on two upright battens to keep them perfectly straight and supported while they acclimatise.
The Right Tools and PPE
Cutting composite is easy, but it generates very fine dust.
- Safety First: Always wear safety goggles, a dust mask, and grip gloves.
- The Toolkit: You will need a tape measure, a reliable spirit level, a pencil, a drill, and a shovel for new posts.
- The Blade: Ensure your circular saw has a fine-toothed blade (a minimum of 40 teeth). Anything less will chew the edges of the board rather than providing a clean, factory-style cut.
Phase 2: The Concrete Post Retrofit
If you are upgrading an old timber fence but keeping the existing slotted concrete posts, this is your route.
A Warning on Bay Widths & Gravel Boards
Decades-old concrete posts move, lean, and settle in the soil. Never assume that because your first bay is 1.83m wide, the rest will be exactly the same. Measure the internal width of every single bay before cutting. Additionally, check your gravel board setup. Most retrofit kits account for a standard 300mm concrete gravel board at the base. If you only have a 150mm gravel board, you will typically need one extra composite board per bay. If you have no gravel board at all, expect to need two extra boards to reach the top.
Securing the Frame
- Slide your provided aluminium U-Channels into the concrete post grooves to check the fit, mark the required height, and cut them to size with your saw.
- Measure the internal distance between the two inserted U-channels.
- Cut your Aluminium Bottom Rail to this exact length, slot it down to sit flush on your gravel board, and check it with a spirit level. If the base isn’t level, the entire panel will lean.
The 4mm Cutting Rule (Crucial)
You cannot cut a composite board to fit tightly against the channels. It must have room to breathe.
- Measure the distance between the U-channels again.
- Deduct exactly 4mm from that number.
- Cutting the board 4mm short provides a vital 2mm expansion gap on the left and a 2mm gap on the right.
- Slide your boards down one by one, allowing the tongue-and-groove system to lock them together. (Never cut a board vertically down its length to narrow it, as you will destroy the locking mechanism).
- Cap it off with the Aluminium Top Rail and your post caps.
Phase 3: Sinking New Posts
If you are building a new boundary line, you will be using aluminium or composite posts.
Why We Don't Recommend Bolt-Down Posts
We are often asked if posts can just be bolted to the ground surface. We strongly advise against this. Solid composite panels catch the wind like a sail. In high winds, the immense leverage placed on the base can rip bolts straight out of the ground. Sinking the posts into concrete is the only way to guarantee a safe, long-lasting installation.
The Excavation and Build
- Clearance: Check for underground pipes or cables, verify if you need planning permission (usually required if over 2m high), and clear away root systems.
- The Dig: Excavate holes to a minimum depth of 500mm. If your garden has particularly soft soil or is in a high-wind area, dig down to 700mm–750mm.
The Pour
- Insert your post, pour in your concrete mix, and use your spirit level to ensure it cures perfectly vertical.
- Expert Tip: Use a pre-cut composite board or a spacer rail between the posts while the concrete sets to ensure the distance is 100% accurate.
The Stack
Once the concrete is fully cured and rigid, insert your bottom rail, slide in your standard 12 boards (remembering your 4mm expansion gaps inside the post channels!), and finish with the top rail.
The Final Walkaround
Before you pack away the tools, run through this quick quality-control checklist to ensure your fence will easily survive the changing UK seasons:
- The 4mm Test: Give the boards a gentle nudge. They should feel slightly loose side-to-side within the channels, not wedged in tight.
- The Base: Is the bottom rail sitting perfectly flat on the gravel board or ground?
- The Cuts: Did you remember to use a 40+ tooth blade for clean edges?
Still have questions or facing a tricky, uneven garden layout? Our technical team is happy to advise on complex installs to ensure you get it right the first time.
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