Our Plastic Decking Joists provide a strong, durable and rot-proof foundation for decking installations, offering a long-lasting alternative to traditional timber subframes.

Made from recycled plastic, these heavy-duty joists are designed for use beneath composite decking and other outdoor decking systems. Unlike timber joists, they won't absorb moisture or rot when exposed to wet ground conditions, helping extend the lifespan of the entire decking structure.

Ideal for decking frames, subframes, terraces, patios and other outdoor structures, recycled plastic decking joists require virtually no maintenance and provide a stable foundation for long-term outdoor use.

For projects where durability and moisture resistance matter, plastic joists for composite decking provide a practical solution that eliminates one of the most common weaknesses of traditional timber decking frames.

Plastic Decking Joists – A Rot-Proof Foundation for Your Deck

A decking system is only as durable as the structure supporting it. Our plastic decking joists provide a strong, moisture-resistant foundation for decking installations, helping create a subframe designed for long-term outdoor use.

Made from recycled plastic, these joists are a practical alternative to traditional timber decking frames. They won't absorb moisture or rot when exposed to damp conditions, making them particularly useful beneath decking where ventilation can be limited and water can collect.

Why Choose Recycled Plastic Decking Joists?

Timber is commonly used to construct decking subframes because it's readily available and relatively inexpensive. However, the supporting structure underneath a deck is also one of the areas most exposed to prolonged moisture.

Even when the decking boards above remain in good condition, deterioration of timber joists underneath can compromise the structure and eventually require sections of the deck to be removed for repairs.

Recycled plastic decking joists eliminate the risk of timber rot, providing a durable foundation designed to remain outdoors throughout the year.

Key Benefits of Plastic Decking Joists

• Will not rot
• Resistant to moisture
• Made from recycled plastic
• UV resistant
• Weather resistant
• Require virtually no maintenance
• Suitable for long-term outdoor installation
• Can be cut, drilled and screwed
• Suitable for composite decking installations
• Ideal for decking subframes and outdoor structures

Plastic Joists for Composite Decking

If you're investing in long-lasting composite decking, it makes sense to consider the lifespan of the supporting structure beneath it.

Installing durable decking boards onto a timber frame can create a mismatch in material lifespan. The visible decking may remain serviceable while the timber subframe underneath begins to deteriorate.

Using plastic joists for composite decking creates a moisture-resistant supporting structure beneath the boards, helping to maximise the long-term benefits of the overall decking system.

A Low-Maintenance Decking Subframe

One of the major advantages of recycled plastic is the minimal maintenance it requires.

Once installed, plastic decking joists don't need painting, staining or preservative treatment. Because the material doesn't rot like timber, there is also no need to routinely treat the subframe to protect it from moisture.

This makes recycled plastic particularly well suited to areas where accessing the supporting frame would be difficult once the decking has been installed.

Suitable for More Than Decking

Although primarily designed for decking frames and subframes, recycled plastic joists can also provide a useful structural profile for other outdoor projects where resistance to moisture is important.

Depending on the project requirements, applications can include:

• Composite decking subframes
• Garden decking
• Terraces
• Patios
• Garden paths
• Raised outdoor structures
• Walkways
• Landscaping projects
• Other moisture-prone outdoor frameworks

Plastic Decking Joists vs Timber Joists

The biggest difference between plastic and timber decking joists is their response to moisture.

Recycled Plastic Decking Joists

• Do not absorb moisture like timber
• Will not rot
• Require minimal maintenance
• Do not require preservative treatments
• Designed for long-term outdoor use

Timber Decking Joists

• Can absorb moisture
• May deteriorate over time
• Can require preservative treatment
• May eventually need replacing
• Replacement can require removal of the decking above

Timber may offer a lower initial purchase price, but the supporting structure should be considered across the expected lifespan of the complete decking installation.

Build Your Deck from the Ground Up

When planning a new deck, it's easy to concentrate on the appearance and finish of the boards you'll see every day. However, the decking subframe underneath is just as important.

Choosing moisture-resistant plastic decking joists helps create a strong foundation without introducing timber underneath a decking system designed for long-term outdoor performance.

Whether you're building a garden deck, terrace or larger outdoor area, recycled plastic joists provide a practical, low-maintenance solution for the structure beneath your decking.

Browse our available Plastic Decking Joists below to compare sizes and specifications for your project.