Decking Installation in Hampshire: Timber vs Composite

Most people planning a deck start with the boards: timber or composite, which colour, grooved or smooth. That matters, but what really decides how long a deck lasts is everything underneath. Hampshire gardens range from heavy clay around Southampton and the Test Valley to thin chalky soils on the downs and sandy ground towards the New Forest, and each behaves differently. This guide walks through how a deck actually goes in, where timber and composite differ during installation, and what to expect on cost and timescale.

Start with the ground, not the boards

A deck is only as good as its footings. Before any timber goes down, the area needs clearing of turf and topsoil, levelling, and covering with a weed membrane so nothing grows up through the gaps. On clay, which swells in wet winters and shrinks in dry summers, footings need to go deep enough to sit below the movement, usually concrete pads or ground screws rather than posts simply dropped into soil. On chalk and sandy ground the challenge is more often drainage and making sure pads do not settle unevenly.

Falls matter too. A deck should run slightly away from the house, roughly 1 in 100, so rainwater sheds rather than pooling against the walls. The finished surface must also stay at least 150mm below the damp-proof course. Plenty of older Hampshire homes have low DPCs or suspended timber floors with air bricks, and covering those vents is a common and expensive mistake. If you are unsure, our exterior carpentry team checks this on the first visit.

The subframe: where timber and composite differ

Whichever boards you choose, the subframe is normally pressure-treated softwood joists, graded for use in ground contact where they sit close to the soil. Some composite systems use aluminium or recycled-plastic joists instead, which will not rot but cost more.

The big difference is joist spacing. Timber boards are usually fixed to joists at around 400mm to 450mm centres. Composite boards are more flexible, so most manufacturers specify closer spacing, often 300mm to 350mm, and sometimes tighter still for diagonal layouts. That means more timber in the frame and more labour, and it is one reason composite decks cost more to install, not just to buy. Ignore the manufacturer's spacing and the boards will sag and the warranty will usually be void.

Ventilation is another point. Composite expands and contracts with temperature, so it needs set gaps at board ends and around walls, plus a clear airflow beneath. Timber needs airflow too, but is more forgiving of a low, tight build.

Fixing, finishing and the details that last

Timber boards are usually screwed down with stainless or coated decking screws, two per joist, with ends pre-drilled to stop splitting. Composite boards are mostly fixed with hidden clips that sit in grooves along the board edges, giving a clean surface with no screw heads. The clips also hold the expansion gaps consistently, which is why fitting them properly takes time.

The finishing details are where a deck looks either professional or home-made:

• Fascia boards around the edges to hide the frame and give a neat line
• Picture-frame borders, where boards run around the perimeter to hide cut ends
• Steps with consistent rise and going, and nosings that are easy to see
• Cut ends of treated timber re-sealed with end-grain preservative
• Balustrades or handrails where the drop or use calls for them

For the full pros and cons of each material, including how they cope in shady gardens, see our honest guide to timber vs composite decking.

Planning, cost and timescale

Most garden decks fall under permitted development as long as the platform is no more than 30cm above the ground and, together with other extensions and outbuildings, covers no more than half the garden. Raised decks, listed buildings and properties in conservation areas, of which Hampshire has many, may need permission, so check with your local council before committing to a raised design.

As a rough guide only, and every job differs, a straightforward softwood deck tends to cost noticeably less per square metre than composite, with hardwood somewhere between or above depending on species. Sloping gardens, raised platforms, steps and awkward access all add to the price. A simple ground-level deck of average size usually takes two to four days to build, while raised or multi-level designs can take a week or more.

Getting your deck built properly

Timber suits people who like a natural look and do not mind an annual clean and treat. Composite suits those who want low upkeep and are happy to spend more at the start. Either will last for many years if the ground preparation, subframe and fixings are done right, and neither will if they are rushed.

PRM Carpentry designs and builds timber and composite decks across Hampshire, from small patios off the kitchen to raised decks on sloping plots. Have a look at our exterior carpentry services, then get in touch for a free, no-obligation quote and an honest view of what will work best in your garden.