Composite Decking Installation: What Good Installers Do

The area is cleared, weeds are dealt with and a membrane is laid to stop growth under the deck. Support points are set on firm ground, on pads or posts depending on the height and the slope. On a sloping garden the frame takes up the difference, so the deck surface finishes level where you want it.

The frame is the structural part of the deck. Joists are spaced to the manufacturer's instructions, which for composite are usually closer than many people expect from timber decking. Wider spacing makes boards feel springy and can void the maker's warranty.

Frames should be square, level and fixed together firmly. Where a deck sits near the house, it must stay below the damp proof course and keep airbricks clear.

Composite boards expand and contract with temperature. Installers leave gaps at board ends, along walls and around posts so the boards can move without buckling. Most systems use hidden clips that hold each board to the joist and set the gap between boards automatically, giving a clean surface with no screw heads.

Air needs to move under a composite deck. Trapped moisture beneath a low deck encourages mould on the underside and can affect the frame. A slight fall along the boards helps rainwater run off, and edges are finished so air can still circulate.

Fascia boards cover the frame edges, and steps are built with the same care as the main deck. Cut ends are trimmed square and edges are aligned so the finished deck looks tidy from the garden, not only from above.

Timing depends on the deck size, the height, the slope, access, and any steps or balustrades. Unlike a patio there is no mortar to cure, so once the deck is finished it can usually be used. We give a timetable with the written quote after a free site visit.

Ask which board system they are fitting and whether they follow its joist spacing and fixing instructions, because the board maker's warranty usually depends on it. Ask how the frame will be supported on your ground, how the deck will be ventilated, and how steps and edges will be finished.

A clear answer to each shows the installer has thought about the structure, not just the boards on top. We explain all of this on the free site visit before sending a fixed written quote.