Composite decking trims: fascia, L-trim, end caps and step edge

A deck is finished at the edges. The boards can be perfect and the frame can be square, and if the cut ends are left open and the joists are on show it still looks like a job half done. Trims are also not just cosmetic: on a hollow board, a capped or covered end keeps water and insects out of the core. This guide explains the four edge parts we sell, where each one goes, and how to work out what your deck needs.

The short answer

Around the outside of a raised deck you need fascia boards to hide the frame. Where a board end meets a wall, a step or another surface you need an L-trim to cover the end and the edge. Every exposed cut end that is not covered by one of those gets an end cap. On steps, a step edge board gives a rounded, non-slip nosing. For a 3.6m by 3m ground-level deck that is two fascia boards, one or two trims and a handful of caps: about £75.

Fascia boards

A flat composite board, 3.6m long, in the same woodgrain finish as the decking, screwed to the outer joist to hide the frame and the board ends. It is the piece that makes a raised deck look like furniture rather than a platform. Ours are £22.99 per 3.6m length in grey, black, teak, oak and chocolate.

How many: the perimeter of the deck that is visible, divided by 3.6, rounded up. A 3.6m by 3m deck against a wall has three visible sides, 9.6m, so three boards; free-standing, four boards. Fix with two screws per joist, pre-drilled 4mm countersunk holes, leaving a 3mm gap under the deck boards above so they can move.

L-trim

An L-shaped profile that wraps a corner: one leg sits on the deck surface over the board ends, the other drops down the edge. Use it on the edge of a ground-level deck where there is no frame to fascia, along a step, and against a wall where the boards end. It hides cut ends without needing a cap on each. 3.6m lengths are £20, 4.8m are £24, in eight finishes to match every board.

How many: the length of every edge where board ends or board edges are exposed at surface level, in lengths of 3.6m or 4.8m. Mitre the corners at 45 degrees. Screw through the vertical leg, not the top, so the fixings are out of sight and the top leg is free to sit flat.

End caps

A push-in plastic cap moulded to the board profile, in a matching colour, that closes the hollow end of a board. £1.49 each in grey, ash, teak, black, oak and chocolate. Use them anywhere a cut end shows and is not covered by fascia or L-trim: the ends of a picture-frame border, board ends along a lawn, boards that run into a gap. They also stop wasps and water getting into the core, which is the reason to fit them even where nobody will look.

How many: count the exposed ends. Two per board on a free-standing ground-level deck with no trim; usually a handful once the fascia and trim have covered the rest. For silver and red brown boards, where there is no matching cap, cover the ends with L-trim or fascia instead.

Step edge

A board with a rounded, grooved nosing on one edge, for the front of each step so the edge is not a sharp cut and there is grip where feet land. 3.6m lengths are £47.99, 4.8m are £62, in grey, black, teak and chocolate. One per step front, cut to the step width. Fix through the face into a double joist behind the nosing.

Worked example: 3.6m by 3m, raised 300mm, against the house

• Fascia: three sides, 9.6m, three boards at £22.99: £69.
• L-trim: none, the fascia covers the edges and the house wall covers the fourth side.
• End caps: the border board ends at the two front corners, four caps: £6.
• Step edge: one step across the 3.6m front: one 3.6m length, £47.99.
• Total trims: about £123 on a deck whose boards cost £500.

Worked example: 3.6m by 3m, ground level on a patio

• Fascia: none, there is no frame height to cover.
• L-trim: around the three open edges, 9.6m, three 3.6m lengths at £20: £60.
• End caps: none needed, the trim covers the ends.
• Total trims: £60.

Fitting rules for all of them

1. Pre-drill every screw hole. Trims split if you drive straight in.
2. Leave expansion gaps at trim ends as you do for boards: 3mm to 9mm depending on the day.
3. Mitre external corners at 45 degrees and fit the mitred pieces before the straight runs.
4. Match the finish to the boards. Every trim comes in the board colours; there is no need to mix.

Order trims with the boards and clips in one go and they arrive together, within 2 to 4 working days. If you send us the deck size and whether it is raised or ground level, we will list exactly which trims and how many. The cost guide has three fully priced decks including trims.