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Composite Decking Types & Prices: A Buyer's Guide
We talk a lot about laying and installing your composite boards, but here is the hard truth: no matter how perfect your installation is, if you don’t get your subframe right, everything else is pointless.
Your subframe is the foundation of your garden project. Selecting the right materials and understanding their pros and cons is the most important step in build your decking right. In the UK, most installations fall into one of two categories: ground-level decks and raised decks.
Here is exactly what you need to know about building a solid foundation for both.
Ground-Level Decking Foundations
When building over existing ground, concrete, or a patio, moisture management is your biggest hurdle. Before laying any frame, always check the existing surface for cracking and ensure there is adequate water drainage
The Composite Batten Approach (Recommended):
For concrete bases, we highly recommend bolting composite battens directly to the ground. Starting at around £15.49, they are competitively priced against timber. Because they are made from HDPE (High-Density Polyethylene), they absorb minimal moisture. You won’t have to worry about the rotting, flaking, or crumbling that eventually ruins timber sitting directly on concrete.
The Timber & Pedestal Approach:
If you are using a timber frame on the ground, you must raise it off the surface. Adjustable decking pedestals are perfect for this. They keep the wood out of standing water, allow for proper drainage, and make it easy to level out uneven ground.
Raised Deck Subframes & Posts
For raised decks, you will need to dig footings and use structural posts to support your joists.
Timber Posts:
The industry standard is 100mm x 100mm timber posts, typically 2.4m in length. You will need to dig 750mm into the ground and secure them with cement.
Tradesman Tip: We highly recommend using C24 grade timber for posts. When installing, slightly curve or bevel the bottom of the post before putting it in the ground. This allows water to run off the bottom rather than soaking up into the end grain!
Composite Posts
Made from dense HDPE, these are the ultimate “fit and forget” solution. While they cost roughly double (and sometimes triple) the price of timber, their longevity is unmatched. They will easily support your subframe for decades. Note: Because of their dense structure, they are harder to work with. You will need the right blades and a slower installation pace.
Choosing Your Joist Material
Once your base or posts are set, you need to select the joists that will directly support your decking boards.
Pressure-Treated Timber (C16)
C16 treated timber is the absolute industry standard for UK decking subframes, offering an exceptional balance of strength and affordability.
The Pros
It is highly cost-effective, easy to work with, and truly tried-and-tested. It creates a robust subframe for raised decks that will easily last over a decade. Plus, because it is the industry standard, installation hardware (like joist hangers) is universally available.
The Cons
It is not great for ground-level decks sitting close to damp surfaces. Compared to composite or aluminium, it has a lower overall lifespan and is ultimately prone to rot, warping, and decay if water drainage isn’t managed properly.
C24 Timber
C24 is highly recommended for long-term structure and strength. C24 offers fewer knots and a tighter grain, meaning it can reach up to almost 50% stronger when compared to C16. This is exactly why it is the go-to choice for heavy structural projects and roof supports.
The Pros:
It is up to 50% stronger and over 30% stiffer than C16, giving much better structural support over the years. It is easy to work with and creates a robust subframe for raised decks that will easily last over a decade.
The Cons:
It is more expensive than standard C16 timber. Additionally, it is not great for ground-level decks sitting close to damp surfaces. Compared to composite or aluminium, it has a lower overall lifespan and is prone to rot, warping, and decay if water drainage isn’t managed properly.
Solid Composite Joists
We are talking about solid core HDPE here, not hollow boards. They come in standard 2×4 sizes and offer incredible durability.
The Pros:
Their lifespan is unmatched—easily outlasting timber by up to 5 times. They are perfect for a “fit and forget” setup for homeowners who plan to stay in their property for 20+ years.
The Cons:
They are the most expensive option, can be tough on saw blades, and require strict adherence to expansion gap guidelines during installation, as plastic expands and contracts with temperature changes.
Aluminium Subframes
Aluminium is lightweight, incredibly strong, and completely resistant to rotting and decay.
The Pros:
Perfectly straight every time, zero rot, and excellent load-bearing capacity.
The Cons:
It comes at a premium price point (more than both timber and composite). Additionally, due to metal expanding and contracting, aluminium frames have been known to cause slight creaking noises underfoot when warming up or cooling down.
| Material | Initial Cost | Lifespan | Workability | Best Application |
|---|---|---|---|---|
| C24 Timber | £10.49 | 10–15 Years | Very Easy | Budget-friendly & standard residential decks |
| Solid Composite | £38.88 | 20–25+ Years | Harder (Dense) | Long-term "fit and forget" residential projects |
| Aluminium | £36 | 30+ Years (No rot) | Easy | Heavy loads & areas with extreme moisture |
The Final Verdict: Which Should You Choose?
The subframe you choose determines the overall lifespan of your deck.
Most customers opt for C24 timber due to its excellent balance of strength and budget-friendly pricing. However, if longevity is your primary goal and you are building a deck for a house you plan to live in for over 20 years, upgrading to a composite or aluminium subframe is absolutely worth the investment.
Ready to gather your materials? Browse our full range of composite decking and subframe materials to get started on your project today.
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