Shopping list for a composite decking terrace: decking boards, joists, fixing clips, trims and supports – a complete checklist.

1. Composite decking boards – the foundation of the whole terrace.

Buy:

• composite decking boards (system/colour to match the design),
• 3–7% extra for cuts and any adjustments.

Tips:

• check the lengths available in the system and plan the layout to minimise waste,
• remember to allow for expansion gaps (composite expands and contracts with temperature — this is normal).

2. Decking joists – the structure that supports everything. 

Without stable joists, even the best composite decking terrace will lose its rigidity.

Buy:

• joists (e.g. composite) with the appropriate cross-section,
• components for joining and levelling (often included with the supports).

Practical tip: before you order, sketch out the layout: the direction of the boards, joist spacing, joint positions and edges. This saves money and stress.

3. Fixing clips + screws – installation can’t get started without them. 

A classic problem: the boards are there, but you’ve ‘run out of clips’. 

Buy:

• starter clips and fixing clips (depending on the system),
• stainless steel screws (usually the best choice for long-lasting use),
• 5–10% extra.

Quick guide to counting clips:

As a guide, the number of fixing points ≈ (number of boards) × (number of joists under each board). Then add extra for joints and edges. 

4. Decking supports / pads – level, slope and ventilation.

If the terrace is to be level, have a slope for water drainage and not ‘rock’, supports do the job.

Buy:

• adjustable supports for joists (when levelling),
• if necessary, solutions for ventilated terraces (e.g. under paving slabs).

Why it’s worth it: easier height adjustment, a tidy space beneath the terrace and better ventilation for the structure.

5. Finishing trims – a ‘wow’ finish and edge protection. 

The finishing touches determine whether the terrace looks complete.

Buy:

• angle trims (corners),
• plinth/cover trims (to close off the sides),
• colour samples if you want to choose in person.

6. Extras that are easy to forget. 

This section often saves your installation weekend:

• tape/insulation under the joists (depending on the substrate),
• spacers and edge components,
• tools: bits, drill bit, spirit level, tape measure, saw,
• if part of the structure is timber: protection/treatment.

As a guide: how much of each item for a 10 m² terrace?

These are quick estimates (exact quantities depend on the dimensions, board direction and joist spacing):

• composite decking boards: approx. 10 m² + 3–7% extra,
• joists: usually approx. 20–30 linear metres (depending on spacing and layout),
• clips + screws: often approx. 180–250 pcs (plus extra),
• finishing trims: according to the perimeter of the terrace (measure the edge lengths),
• supports: number of support points under the joists (depends on the substrate and height).

Most common mistakes (and how to avoid them). 

• Buying only the boards without an installation system → no clips/screws = work stops.
• Too few joists or incorrect spacing → deflection and durability problems.
• No plan for finishing the sides → the terrace works, but looks ‘unfinished’.
• No supports/levelling → puddles and struggling to get the fall right.

Checklist to copy and paste. 

composite decking boards (+ 3–7% extra)

decking joists (composite/aluminium)

starter clips + fixing clips

stainless steel screws (+ 5–10% extra)

adjustable decking supports / pads

skirting boards + corner / cover trims

joist tape/insulation, spacers, edge components

tools: bits, drill bit, spirit level, saw, tape measure

FAQ - Frequently asked questions.

Does a composite deck need expansion gaps?
Yes — composite material expands and contracts with temperature, so installation gaps are essential.

Do I need adjustable supports?
Not always, but they make things much easier on uneven ground and when you want to create an even fall.

How much extra decking should I buy?
Usually 3–7% is enough; for complex shapes, it is better to allow closer to 7–10%. 

In conclusion. 

If you've been thinking about building your own composite deck, honestly — it's well worth doing. A project like this delivers a quick ‘wow’ effect, and with the right installation system, the work goes more smoothly than you might think. The key is simple: put together the complete composite decking shopping list (decking boards, decking joists, fixing clips with screws, finishing trims and adjustable supports), then work through it step by step, without delays caused by missing little bits and pieces.

To avoid mixing components from different systems and to make sure everything works together, the easiest option is to choose everything in one place. At gardpol.pl you'll find composite decking boards (for example, in the DUO and PREMIUM systems) and dedicated installation accessories — exactly what you need to make your deck stable, attractive and finished down to the last detail. If you like, copy the checklist from this post, add the items to your basket and build a deck you can be proud of — coffee tastes completely different outdoors.