How to install the joists for your outdoor decking
A successful deck is not just about the timber, but about what sits underneath it. A well-built substructure is the difference between a floor that lasts decades and one that warps in two years. These are the critical points.
1. The joist: the backbone
The joist is the foundation of your floor. Get the structure wrong and the timber will warp. Three golden rules:
- Levelling and drainage: keep a minimum fall of 1-2%. Water must never sit under the decking; trapped moisture is the worst enemy.
- Technical spacing: leave no more than 35-40 cm between joist centres. Go wider and ipe or iroko boards will flex underfoot.
- Quality material: use tropical hardwood or aluminium joists. Never untreated pine, as it will rot long before the decking does.
2. The fixings: the detail that changes everything
Never use ordinary steel screws. Tropical hardwood contains tannins that react with the metal and create indelible black stains on the surface.
Professional recommendation: class C4. For high-end installations and thick boards, we insist on screws certified to class C4 coating. They guarantee complete corrosion resistance, even in coastal areas or in very damp conditions. You can find them here: CAMO class C4 hidden-fixing screws.
Important: because ipe and iroko are so dense, pre-drilling is essential. Without it, screws can snap as they try to bite into the solid fibre.
Frequently asked questions
How far apart should the joists go?
A maximum of 35-40 cm between centres. Any wider and the decking flexes.
Can I use pine joists?
Only if they are treated for outdoor use to class 4, and even then they will last less than the decking. Tropical hardwood or aluminium joists are the better choice.
Why is pre-drilling necessary?
Because ipe and iroko are so dense that without a pilot hole the screw can snap or go in crooked.
Everything for your installation
Find decking boards, joists and fixings in our outdoor decking collection. Questions about your project? Write to us at info@kamikspace.com and we will point you in the right direction.
Natalia · Kamik Space
