How to fit composite cladding

Video by EnviroBuild. This guide draws on "How to Install Composite Cladding" from EnviroBuild, a UK-based composite decking and cladding company. Their installation video covers the full process clearly, including the clip system and corner trim details that trip people up on a first install.

1. Understand the system

Composite cladding boards are made from a mix of recycled wood fibre and plastic. They do not rot, they do not need painting, and they hold their colour far better than timber. The boards are typically hollow-profile and clip together using a hidden fixing system — T-clips or C-clips that locate into the board grooves and screw to the battens behind.

The key thing to understand before you start is that composite boards expand and contract with temperature. Every board needs an expansion gap at each end, and the clips hold the boards while allowing lateral movement. Follow the manufacturer’s gap requirements exactly — skipping this is the main reason boards buckle in summer.

2. Check the substrate and plan the layout

Composite cladding needs a timber batten framework fixed to the wall behind it. The wall itself needs to be sound — loose render, crumbling mortar, or soft masonry should be addressed before you start. Any damp issues in the wall need resolving too; composite boards are waterproof on the face, but you do not want moisture trapped behind them with nowhere to go.

Plan the board layout on paper first. Work out where you want the boards to start and finish vertically, and whether you need cut pieces at the top or bottom. A symmetrical layout with equal cuts at top and bottom looks more intentional than full boards at the bottom and a narrow strip at the top.

3. Install the battens

Fix horizontal timber battens to the wall at the spacing required by the board manufacturer — typically every 400–600mm, depending on board length and the loading specification. Use 50×38mm treated timber for the battens and fix them with frame fixings into masonry, or screws into timber-frame walls.

Use a spirit level on every batten. The battens do not need to follow the wall — they need to be in a single flat plane. Pack out low spots with slate or plastic packers to bring each batten flush with its neighbours. Any deviation in the batten plane will show in the finished cladding.

4. Fix the starter strip

The bottom of the cladding run starts with a starter strip or a J-channel fixed to the lowest batten. This holds the bottom edge of the first board, sets it at the correct angle, and keeps it in place while you fix the first row of clips above it.

The starter strip should be level. Check it with a long spirit level across the full width of the wall before fixing. An out-of-level start will compound with every board you add above it.

5. Clip and fix the boards

Locate the first board into the starter strip and push it gently home. Place a clip into the top groove of the board at each batten position and screw it down. The clip simultaneously holds the first board and creates the socket for the bottom of the next board. Work across the wall before moving up.

Allow the correct expansion gap at each end of every board. For most composite systems this is 5–8mm. Use a spacer cut from offcut material to keep the gap consistent. At inside corners, cut the boards to finish flush with the corner and trim with an aluminium or composite corner section.

6. Trim around openings

Windows and door openings need J-channel or trim pieces fitted before the boards go in around them. The board ends locate into the trim channel, which gives a clean finish and stops water getting behind the cladding at the opening edges. Measure carefully — boards cut to fit around an opening need to be accurate to within a couple of millimetres.

Seal any gaps between the trim and the wall frame or render with a good quality exterior sealant. This is the point at which water most often finds its way behind cladding on a poorly finished job.

7. Fit the corner trim and top finish

Outside corners take a corner post or an H-section trim that the board ends clip into. Fix the corner post first, then slide the boards in as you work up. At the top of the wall, a top trim or fascia section covers the top edge of the last board and closes off the ventilation cavity above.

Most composite systems have matching trim pieces in the same colour and finish as the boards. Use them — improvising with aluminium flashing or timber at the corners and top looks unfinished and does not last as well.

When to call a handyman

Call Richard if the wall has damp problems that need sorting first, if the substrate is uneven enough to need significant packing, or if the installation wraps around a bay window or involves complex angles. First-floor and above work also benefits from a second pair of hands for handling the boards and working at height safely.