Composite Decking Boards: Sizes, Spacing, Clips and Screws

Decking board sizes and product descriptions

Check the selected product’s actual face width, thickness, available length, groove profile and intended use. Composite decking can use different polymer and fibre formulations; solid, semi-solid, hollow and capped are product descriptions, not interchangeable strength grades. A cap or outer layer does not by itself establish load capacity, slip performance or all-round protection of cut ends. Plastic decking, composite and pressure-treated pine have different material and installation requirements. Use the exact technical specification rather than treating every wood-look board as the same product.

Decking board spacing and supporting structure

Side gaps, internal end gaps and clearances against walls or posts can serve different purposes and are not interchangeable. Composite movement can depend on the product and installation conditions; timber dimensions can change with moisture. Use the current manufacturer’s instructions for the actual board, clip, framing material and layout. This tool does not pick joist spacing, spans, overhang, foundations, drainage fall, ventilation or railings. Angled boards, borders and joints can need different support details from straight uninterrupted rows.

Composite decking board clips and screws

A hidden clip can engage adjacent grooved boards, while a face-fixed system can use a different fixing pattern. Starter, finishing, butt-joint and edge details may need distinct hardware. The optional fixing estimate therefore covers one specified hardware product only, entered either as a planned count or as total specified fastening positions multiplied by units of that product per position. Those positions must come from the checked layout. Do not assume one clip equals one face screw or combine different product types in one pack count.

How many decking screws per board?

For an approved face-fixed arrangement, a board segment’s fixing quantity can be calculated from its actual supported fastening positions multiplied by the specified number of screws at each position, with any additional details counted separately. Neither figure is universal. A short cut, butt joint or doubled support can change the schedule. Enter total fastening positions from the actual layout if using rate mode; the calculator does not derive them from an assumed joist interval. Board purchase spares do not automatically create installed fixing positions.

Choosing a design and checking the order

Straight rectangular rows are the scope of this estimator. Herringbone, diagonal cuts, curves, picture frames, breaker boards, steps, edge boards, fascia and penetrations require their own cutting and support details. A decking board bender or a curved appearance does not establish that a product can be bent or heated safely; use a manufacturer-approved method and specialist fabrication where applicable. Check the order against the drawings and selected product before buying. No current retailer price or UK stock range, including Wickes, is assumed to match South African availability.

Frequently asked questions

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