Most common construction of house slabs is traditional hardfill, boxing, polythene and mesh system or waffle pod/Ribraft concrete floor systems are now widely used.

Concrete slab construction is now the most common way to lay a ground floor on flat ground.

Thermal mass

In winter, a slab floor can absorb solar heat and then radiate it out during the evening to keep your home warm. It should be insulated underneath and around the edges to stop heat escaping into the ground

Concrete takes at least four months to dry out – longer in winter – and it will not perform well as a thermal mass until it is dry.

If you’re using concrete as a source of warmth, don’t cover it with carpet where the sun shines on it – this stops the slab from warming up. However, not having a floor covering can also make the concrete floor less forgiving if you trip or fall. Consider partially covering the slab – for example, with exposed concrete or tiles around the perimeter and carpet or mats in the centre.

Reinforcing

All concrete floor slabs on ‘good ground’ are required to have reinforcing steel mesh and all perimeter foundations are required to be tied to the concrete slab with reinforcing steel; you can’t use unreinforced slabs anywhere in New Zealand.

The purpose of the mesh is to stop or limit the spread of a crack if it opens up. Without mesh, a crack in an unreinforced slab is likely to widen and spread across the whole slab. Tying the perimeter foundation to the slab reinforcement limits movement and damage from earthquake shaking. Large slabs are designed to have some movement joints.

Heating systems

Slabs can have water pipes or electrical cables embedded in them for heating.

Insulation

In most climate conditions a concrete slab will need to be insulated around the edge, and underneath, this can be done using polystyrene

Suspended floors

Commercial buildings usually have reinforced concrete slab floors on all levels. These slabs can be pre-cast to speed on-site construction. This can also be done in domestic construction but will need to be insulated on the underside.