Wooden or aluminium joists – which are better for decking?

What exactly are joists, and why are they so important?

Joists are horizontal load-bearing beams that form the framework of a deck. They are installed on a prepared base – concrete, pad foundations or supports – and the decking boards are laid on top. Properly selected joists affect:

• the strength of the entire structure,

• resistance to deformation,

• the durability of finishing materials,

• safety in use.

That's why choosing between wooden and aluminium joists is not just a matter of budget, but above all of practicality and comfort for years to come. 

Joist comparison – a quick-reference table.

Wooden joists – a classic with its pros and cons

Advantages:

1. Natural look and aesthetics
   Wooden joists (most commonly pine, spruce, larch or exotic hardwood) fit perfectly with the look of decking made from natural boards.

2. Lower purchase cost
   Wood is cheaper to buy than aluminium, which can make a difference over large areas.

3. Easy to work with
   Wood can easily be cut, drilled and adapted to uneven ground or unusual shapes.

4. Material availability
   Wooden joists are widely available from DIY stores and timber merchants.

Disadvantages:

1. Require treatment and regular maintenance
   Even if pressure-treated, wood can rot, absorb water or biodegrade over time.

2. Less resistant to moisture and pests
   Depending on the quality of the wood, the risk of biological damage (fungi, mould, insects) can be considerable.

3. Less dimensional stability
   Wood moves in response to temperature and moisture – it can warp or crack.

Aluminium joists – a premium, modern solution

Advantages:

1. Durability and resistance to the weather
   Aluminium does not corrode, absorb moisture or rot, and requires no maintenance.

2. Lightweight yet highly durable
   Despite their low weight, aluminium joists offer high resistance to loads and mechanical damage.

3. Excellent stability
   They do not move like wood – they do not change dimensions, crack or warp.

4. Long service life
   Aluminium structures can last for several decades without needing replacement.

5. Maintenance-free
   An ideal solution for anyone looking for years of ‘peace of mind’.

Disadvantages:

1. Higher price
   Aluminium joists can cost 2–3 times as much to buy as wooden ones.

2. Require precise installation
   Cutting or fastening them may require specialist tools (e.g. for metal).

3. Lack the ‘warmth’ of wood
   Although they are aesthetically pleasing, they will not give your decking the same character as natural wood.

When should you choose wooden joists?

Wooden joists are a good choice if:

• You have a limited budget.

• You are building a small deck (e.g. beside a holiday cottage).

• You are using natural decking boards and want to keep the materials consistent.

• You are prepared to carry out regular maintenance.

Tip: Choose only certified, well-treated wood. Exotic hardwood (e.g. bangkirai) is a better choice, as it is naturally resistant to moisture and pests.

When is it worth investing in aluminium joists?

Aluminium joists are a good choice when:

• The deck is large and will be used intensively.

• You want to avoid any maintenance in the future.

• Maximum durability and safety are important to you.

• You are building a modern deck, for example with composite decking boards.

Pro tip: Aluminium joists are recommended for composite decking boards – manufacturers often offer a longer warranty in that case.

What practical experience tells us – installers’ views

Most experienced decking installers say that:

• Wooden joists are OK for short-term realisation or with a limited budget.

• Aluminium joists are an investment in comfort and peace of mind for years to come.

If you plan to use your terrace for 10–20 years, it is worth paying extra for a sturdier structure.