5 min read
The short version
Choose composite if you do not want to maintain it. Choose hardwood if you want it to look like real timber and are willing to oil it, or are content to let it silver.
Composite costs more up front and almost nothing thereafter. Hardwood costs less up front, more over time, and rewards the attention with a material nothing synthetic quite matches.
Composite: what it is and how it fails
Composite boards are wood fibre and plastic. Modern boards are capped — a polymer shell bonded over the core — and capping is the single most important thing to ask about. Early uncapped composite stained, faded badly and grew mould in the grooves, which is where composite's mixed reputation comes from. Capped boards resist all three.
It does not rot, splinter or need oiling. It fades slightly in the first year and then stops. In a London garden that is often shaded and damp for months at a time, that resistance to algae and moisture is worth a great deal.
Where it disappoints is heat and repair. Dark boards get genuinely hot in direct summer sun, and a deep scratch or scorch cannot be sanded out the way timber can — the cap is the surface. It also does not look like wood close up, however good the embossing.
Hardwood: what it is and how it ages
Dense tropical hardwoods — balau, ipe, iroko — are naturally durable enough to last decades outdoors without chemical treatment. They are heavy, hard on tools, and they look like what they are.
Left alone, hardwood weathers to a soft silver grey. Many people want exactly this. If you want the original honey or chocolate tone, it needs oiling, realistically once a year in a British climate, and skipping it is not a disaster — it is cosmetic, not structural.
The two things to watch are movement and sourcing. Hardwood expands and contracts with moisture, so boards need laying with the right gaps and fixing in a way that allows it. And tropical hardwood should be FSC certified or equivalent; the alternative has a real cost somewhere else in the world.
The substructure decides the lifespan
This is the part that matters more than the board choice and gets the least attention in quotes. A deck fails from underneath, almost always.
Joists must be pressure-treated to a grade suitable for ground contact if they are anywhere near it, set at the spacing the board manufacturer specifies, and supported on concrete pads or posts rather than resting on soil. Composite boards typically need closer joist centres than timber, and a frame built to timber spacing under composite boards will bounce and sag — a common and entirely avoidable fault.
Where ground moisture is unavoidable — a low deck, a shaded corner, clay that stays wet — an aluminium subframe removes the failure mode altogether. It costs more and it will outlive everything above it.
- Ventilation
- Air must move under the deck. A sealed-in frame over damp clay rots regardless of what it is made from.
- Fall
- A slight slope away from the house so water sheets off rather than sitting in the grooves.
- Membrane
- Weed membrane under the whole footprint, before the frame goes down. Retrofitting it is impossible.
- Fixings
- Stainless or coated to suit the timber — some hardwoods corrode ordinary steel and stain around every screw.
The London factor: shade and damp
Most London gardens are enclosed on three sides and get direct sun for only part of the day. North-facing plots get very little. That microclimate is hard on decking of any kind: surfaces stay wet, and anything that stays wet grows algae, which is what makes a deck slippery in winter.
Both materials handle this better than softwood does, and both benefit from the same things — grooves running the way water drains, air beneath, and a wash-down once or twice a year. Composite has the edge in permanent shade, simply because there is nothing organic on the surface for algae to key into.
So which one
If the deck is the main surface you will use daily, sits in shade, and you would rather not think about it again: composite, capped, on a frame built to the manufacturer's spacing.
If it is a feature you want to look and feel like timber, gets reasonable sun, and you do not mind an afternoon with a bottle of oil each spring: hardwood, FSC certified, fixed to allow movement.
Either way, spend the money on the frame. Boards can be replaced in a weekend in fifteen years. A failed substructure means taking the whole thing up.
- Does composite decking get slippery?
- Less than timber, but nothing is immune in a shaded, damp London garden. Slipperiness comes from algae growing on the surface rather than from the material itself, and capped composite gives algae less to hold onto. Grooved boards laid so water runs along the grooves, good airflow underneath, and an occasional wash keep any deck safe through winter.
- How long does each one last?
- Both outlast the frame if the frame is poor, and both last a very long time if it is good. Quality capped composite and dense hardwood are each realistically multi-decade materials in a domestic garden. That is why the substructure specification is the question worth interrogating in a quote — not which board is more durable.
- Can decking be laid over an existing patio?
- Often, yes, and it can be a sensible way to raise a level or cover a tired surface without excavation. The requirements are the same as anywhere: the frame must be supported properly, there must be airflow beneath, water must be able to escape rather than pond on the old slabs, and the finished height must still work with door thresholds and any damp-proof course.