Introduction
When it comes to building a long-lasting, safe, and visually stunning deck, what lies beneath matters just as much as the boards you see. The subframe is the structure that supports your decking — and choosing the right one can significantly affect its durability, performance, and maintenance requirements.
In this guide, we break down the three main subframe options available today: timber, recycled plastic, and aluminium hybrid systems. Whether you're building a small backyard deck or a complex multi-level space, the right subframe can make all the difference.
Timber Subframes: Traditional but Maintenance-Heavy
Softwood timber is the most common material used for decking subframes. Due to the natural properties of timber, it is important to ensure the correct Use Class is purchased. Timber subframes should be clear of the ground and must have an airflow ventilation gap around the outside, and a free air space across the whole underside of the frame that will not impede the free flow of air.
Timber has long been the go-to material for deck subframes. It's easy to work with, cost-effective, and provides strong structural support.
Pros:
- Widely available and affordable
- High strength-to-weight ratio
- Easy to cut and install with standard tools
Cons:
- Requires pressure treatment (Use Class 4) to resist rot
- Needs good airflow to avoid moisture build-up
- Ongoing maintenance is essential to prevent decay
Timber remains a solid choice for those on a budget or working with familiar materials — but it may not be the best long-term option in damp or shaded gardens.
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Plas-Pro: Recycled Plastic for Damp or Ground-Level Sites
Plas-Pro is Millboard’s subframe made entirely from recycled plastic. It’s ideal for installations where timber would quickly degrade, such as directly on the ground or in high-moisture environments.
Pros:
- 100% resistant to rot, moisture and insect attack
- Made from recycled materials
- Low maintenance and long-lasting
Cons:
- Slightly heavier than timber
- Colour and surface texture may vary due to recycled content
Plas-Pro is particularly suited to garden rooms, hot tub platforms, or decking on soft or damp terrain where traditional materials would struggle.
DuoSpan®: Aluminium Hybrid Subframes for Ultimate Stability
Millboard's DuoSpan system combines the precision of aluminium with the environmental credentials of recycled plastic, offering an advanced, robust solution for high-spec or complex decking projects.
Pros:
- Excellent structural strength
- Resistant to moisture, rot and UV degradation
- Allows for intricate designs, curves and multi-level layouts
- Compatible with top-down fixings for a clean finish
Cons:
- Avoid direct contact with other metals to prevent corrosion
- Requires care in very alkaline or acidic soil conditions
DuoSpan is ideal for elevated decks, commercial projects, or where long-term performance and low maintenance are priorities.
Side-by-Side Comparison
How to Choose the Right Subframe
The best subframe for your project depends on:
Location and environment: Damp ground? Choose Plas-Pro. Sloped or complex site? Go for DuoSpan.
Design requirements: Curved or multi-level layout? DuoSpan offers maximum flexibility.
Budget: Timber is budget-friendly upfront but may cost more in maintenance over time. If you're not sure, speak to a professional or one of Millboard's Approved Installers for site-specific advice.
Conclusion
Your decking subframe isn’t something you see — but it plays a vital role in how your deck performs and how long it lasts. Timber might suit basic projects, but for low-maintenance or high-performance builds, systems like Plas-Pro and DuoSpan offer greater peace of mind.
To learn more about Millboard’s subframe systems, download our installation guides or get in touch for tailored support.