Composite decking fixings and clips: how many do I need?

What fixings does composite decking need?

Hidden clips for the boards in the middle of the deck, screws through the face for the first and last boards, and trim for the edges. The catalogue sells Composite Decking Clips and Composite Corner Trim. Add clips to the order with the 3.6m composite decking: they are sold in quantities of 100 and 200.

The frame matters as much as the fixings, and every figure below assumes the one in the laying guide: joists at 400mm centres for boards laid square, 300mm centres for a 45 degree diagonal lay, 5 to 6mm between boards, and at least 25mm of ventilation underneath.

How do the hidden clips work?

Each clip is a T-shaped holder with a screw. It sits in the groove on the edge of a board and the screw goes down into the joist. The next board is pushed up against the clip, and the clip sets the gap between them. Nothing shows on the walking surface.

Fit one clip per board at every joist it crosses, then lay the next board and repeat. Check every few rows that the boards are still square to the first one, and straighten a board before its screw goes home.

How many clips per board and per square metre?

Allow 11 to 13 clips per 3.6m board, or about 23 per square metre. A bare count from the joist plan gives a similar answer. A 3.6m board with joists at 400mm centres lands on about ten joists, and at 300mm centres on thirteen, so the 11 to 13 range sits between the two spacings.

Order from the 11 to 13 figure, then round up to the next quantity. The table shows what each quantity fixes, rounded down to leave a margin.

Composite decking clips: what each quantity fixes

Clips ordered	How made up	Boards at 11 to 13 each	Deck area at about 23 per m²
100	One quantity of 100	7 to 9	4.3m²
200	One quantity of 200	15 to 18	8.7m²
300	200 plus 100	23 to 27	13.0m²
400	Two of 200	30 to 36	17.4m²

A 10m² deck, for example, needs about 230 clips at that rate, so order 300. The guide how much composite decking do I need works the boards and clips out together from a plan.

What comes in a pack?

The clips are sold as a quantity of 100 or 200 on one product page. Each clip includes a T-shaped holder and a screw, so the screws for the field of the deck come with the clips. Add the clips to the same order as the boards. If you are close to a pack size, take the larger one, so you can finish the deck in one go.

How do I fix the first and last boards?

Through the face. The laying guide says to face fix the first and last boards and any board beyond the reach of a clip: pre-drill and countersink every hole, at least 5mm in from the board edge, then screw into the joist. The first board has a clip on its inside edge and the last board has a clip on its outside edge, so the screws through the face hold down the other edge.

Ask at the counter for the fixings for the first and last boards, and say what the joists are made of so we can pick them with you.

Three rules apply to the edges whichever method you use:

• Leave 10mm minimum between the boards and any wall or fixed object.
• Keep the overhang past the last joist to 25mm or less.
• Where two board ends meet, use a doubled joist so each end has its own fixing, and leave 6mm between them on a 3.6m board.

How do I finish the edges?

With corner trim. It is an L profile, 3,600 x 40 x 40mm, in charcoal or grey. It fixes with adhesive or countersunk screws. The laying guide recommends fixing through the face into the joist end or a batten behind it, using stainless colour-head fixings that keep the board face clean, and mitring outside corners at 45 degrees. Leave the same gap behind the trim that you left everywhere else.

If you would rather bond the trim, two adhesives in the catalogue say they work outside. Everbuild Multi Stick is an MS polymer grab adhesive that bonds in wet and dry conditions, including to hard plastic, metals and timber. Soudal Fix All Flexi is a black MS polymer sealant and adhesive for interior and exterior use. Ask which suits your trim colour before you buy. The full range is in adhesives.

How do I get the fixings right?

Four points come up at the counter.

• Order the next quantity of clips up, so there are enough for the last boards.
• Leave 5 to 6mm between boards and 6mm where two board ends meet. The clip sets the side gap.
• Fix clips into joists that are level with their neighbours: check the frame with a straightedge before the first board goes down.
• Finish cut ends with corner trim, and order it with the boards.

Where can I get composite decking fixings in Liverpool?

Collect free from the Liverpool showroom at Unit 7, The Boxworks, Heysham Road, L30 6UR. We are open Monday to Friday 7:30am to 4:30pm and Saturday 7:30am to 1pm, to trade and public. Delivery is priced by postcode and shown on each product page and at checkout. Bring your joist plan and we will check the clip count with you. The whole range is in composite decking.