Decking (decking slab, suspended slab)

In a single-storey bungalow, the roof sits on the walls. In a storey building, each upper floor needs a structural slab that spans between beams and columns. Builders in Nigeria call casting that slab "decking".

The process. Timber or steel formwork and props are set up at the level of the upper floor; reinforcement is laid; and concrete is poured, often in one day, by a gang with mixers or ready-mix trucks. The props stay until the concrete has gained enough strength.

Hollow-block decking. Some designs use hollow clay or sandcrete blocks between concrete ribs to reduce weight and material. This is a structural choice for the engineer, not a short cut.

Where it sits. After lintel level on the ground floor, the decking is cast; then walls rise for the next floor, with their own lintels, and finally the roof. Builders track progress and payments by these stages.

Why buyers care. The decking carries the weight of the upper floor and everyone on it. Poor concrete or too little reinforcement can lead to cracks, sagging or worse.

Cost and planning. Decking needs a large quantity of cement, sand, granite and iron rods at once, plus formwork, props and labour on the day. Builders often schedule it as a single big payment milestone. Weather matters too: casting in heavy rain affects the concrete, so many sites plan the pour carefully.

Buying a building at decking. If you are buying a partly built storey house, ask for the drawings, approval and the engineer's casting records, and have the slab inspected before you pay.

Decking and roof slabs. Some modern houses also use a concrete slab as a flat roof or roof terrace. That slab is cast in the same way as an upper-floor decking and needs careful waterproofing.

• Across Nigeria: cast-in-place reinforced concrete decking is standard for duplexes and blocks of flats.
• Some projects: precast or hollow-block systems are used to save formwork.