3100 × 40 × 30 mm Joists & accessories
Outdoor
Joists &
installation accessories
What you stop seeing once the terrace is laid, and what nonetheless decides how it holds up over ten years.
- Products
- 01
- Lengths
- 3100 mm
- Thicknesses
- 30 mm
- Quote
- 24 h
3100 × 40 × 30 mm Choosing well
The four things to check
01
Same material
A WPC structure under WPC boards: the whole assembly expands and ages at the same rate.
02
40 × 30 mm
A section calibrated for 40 to 50 cm centres in normal residential use.
03
Rot-proof
No rot, no termites, no swelling — even in permanent contact with damp.
04
3.10 m
Same length as the boards: quantity calculations and offcuts stay simple.
A composite terrace is two products: the boards you see and the joist you no longer do. The second decides everything. An undersized, poorly ventilated or untreated timber substructure eventually gives you a deck that waves, creaks and steps out of level.
Why a composite joist
Laying rot-proof boards on timber joists is a common inconsistency: the structure rots before the surface does. Our WPC joist, 3100 × 40 × 30 mm in teak brown, shares the composition of the boards — same water resistance, same dimensional stability, same service life. The whole assembly ages as one.
Sizing
For a 22 mm board in residential use, lay joists perpendicular to the boards, 40 to 50 cm centre to centre. Tighten to 35 cm under a hot tub, a planter or any load point. For a 45° diagonal layout, always reduce the centres by 10 cm, since the board's real span increases.
The three rules of the substructure
Ventilate. At least 20 mm of clear space under the joists, never direct contact with soil and never backfill closing the gap.
Drain. A 1 % fall in the direction of run-off, achieved by adjusting the pedestals, not by planing the joists.
Isolate. 10 to 20 mm between the structure and any adjacent wall, to absorb expansion without restraint.
Frequently asked questions
What we get asked
most often
Can timber joists be used under composite boards?
It is possible but inconsistent: your structure will degrade before your surface, and replacing joists means lifting the entire terrace. If you insist, demand at minimum autoclave-treated class 4 timber.
How many metres of joist for 30 m²?
At 45 cm centres on a 30 m² terrace (6 × 5 m), allow roughly 14 runs of 5 m, so 70 linear metres, plus edge reinforcement and joints at board ends. We do this take-off with you from your plan.
Should joists sit on pedestals?
On a slab it is the best solution: adjustable pedestals take up level differences, set the fall and guarantee ventilation. On stabilised ground, composite shims or isolated concrete pads do the same job.
The other range
Interior wall coverings
Marble-effect SPC panels and decorative slat boards