Build cost, board by board
A low softwood deck on reasonably level ground works out around £125 to £215 per square metre fitted. The same deck in composite runs around £225 to £370 per square metre, because the boards themselves are two to three times the price.
Neither figure means much on its own until you know the height, which is the part most online calculators ignore completely.
Why height costs more than size
A deck sitting 100mm off the ground needs pads, bearers and joists. Lift the same deck a metre to meet a back door and it needs posts, footings, bracing, a balustrade and steps, and the timber underneath can cost more than the boards on top.
If your garden falls away from the house, expect the subframe to be the largest line on the quote. It is also the line that decides whether the deck feels solid underfoot in five years.
The ten year comparison
Softwood needs cleaning each spring and a coat of oil or stain roughly every year or two. Over ten years that is a real cost in materials and a real cost in weekends.
Composite asks for a wash and very little else. On a 15 square metre deck the extra outlay at the start is usually recovered somewhere around year seven, sooner if you would have paid someone else to do the upkeep.
Getting the size right
For a table and six chairs you want around 4 by 4 metres of clear deck. Add a barbecue or a corner sofa and it grows quickly. Measure your furniture with the chairs pulled out and work back from there rather than picking a round number.
Guide decking prices
Guide figures for Southampton and the surrounding towns. Sloping sites are quoted after a site visit.