How many clips do I need per m2 of composite decking?

The number of clips depends on joist spacing and board width. At 350mm joist spacing with 140mm boards, you need approximately 20 clips per m². Each board-joist intersection requires one clip. Plus starter clips along the first board and end clips for the last board. We recommend ordering 10% extra.

What joist spacing should I use for composite decking?

Most composite decking manufacturers recommend 300-400mm joist centres. Use 300mm for heavy-traffic areas, hot tubs or diagonal board layouts. Standard domestic use is 350mm. Never exceed the manufacturer's maximum spacing — composite boards can flex more than timber under load.

Do composite decking boards need expansion gaps?

Yes, composite decking expands and contracts with temperature changes. Leave a 5mm gap between board edges (maintained by the clip system) and 10-15mm at each end of the boards against walls or fixed structures. In hot weather, boards can expand by up to 3mm per linear metre.

Can I use timber joists with composite boards?

While possible, composite or aluminium joists are recommended for longevity. Timber joists (treated C16/C24) will deteriorate before composite boards which last 25+ years. If using timber, ensure it's pressure-treated to UC4 hazard class. Aluminium joists are the premium option for a truly maintenance-free deck.

What is fascia board for decking?

Fascia boards cover the exposed ends and edges of the deck frame, giving a neat finished appearance. They also protect the cut ends of boards from moisture ingress. Fascia is measured by the perimeter of exposed deck edges. Corner trims and L-profiles are available for neat joins.

TradeCalculator

Composite Decking Calculator — Boards, Joists & Clips

Calculate composite decking boards, joists, clips, starter/end clips and fascia for your deck.

Deck Length

Length parallel to boards

Deck Width

Width across boards

Board Width

Joist Spacing

Board Price

Per linear metre of board

Joist Price

Fascia Run

Total exposed edge length

How We Calculate This

This calculator determines composite decking board quantities, joist counts, fixing clips and fascia trim based on your deck dimensions.

Board quantity

Boards = ceil(Deck Width / (Board Width + Gap)) x Deck Length
Joists = ceil(Deck Length / Joist Spacing) + 1
Clips = Boards across x Joists across

Accessories

Starter clips fix the first board to each joist. End clips secure the last board. Expansion gaps of 5mm between boards are maintained by the hidden clip system.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.