Slab Works

Design slabs to absorb heat from the sun or other sources during winter. Heat can be stored in the slab and reradiated for many hours afterwards. In summer, allow slabs to be exposed to cooling night breezes so that heat collected during the day can dissipate. Passive solar design principles and high mass construction work well together, and concrete slabs are generally the easiest way to add thermal mass to a house. Living rooms should face north in all but warm and high humidity climates to enable winter sun to invest warmth into the slab. Concrete slabs perform better as the diurnal temperature range increases (temperature difference between the minimum at night (low) and the maximum during the day (high).

If reinforcement is correctly designed and placed,and if the concrete is placed and compacted well so there are no voids or porous areas,concrete slabs have a long lifespan. Compaction is usually achieved by vibrating the concrete. This reduces the air entrapped in the concrete giving a denser, stronger and more durable concrete better able to resist shrinkage cracking. While deeper beams should be compacted, thin slabs (100mm-thick typically) receive adequate compaction through the placing, screeding and finishing operations.

Curing of all cement-based building materials is critical to achieving the design strength and other desired properties, especially with structural concrete slabs. Concrete takes 28 days to reach the design strength, although a sufficient minimum design strength may be achieved in less time if the concrete is specified accordingly. It is essential that the curing regime specified by the design engineer is followed exactly.

Termite resistance is achieved with concrete slabs by designing and constructing them in accordance with the Australian Standards to minimise shrinkage cracking, and by treating any joints, penetrations and the edge of the slab.

Level sites are best suited to slab-on-ground construction. Use of slab-on-ground allows earth coupling and, because floor levels are close to ground level, facilitates free flow from interior to exterior spaces.
Steep sites may have geotechnical requirements which make slab-on-ground construction impracticable. Although slab-onground construction is more thermally efficient, a suspended slab can be a suitable way to gain the advantage of thermal mass on a steep site. Typical pole frame construction can be adapted easily to incorporate a slab. The slab underside should be insulated in some climates.

Natural ventilation must be provided for in the design. On summer evenings, heat stored in the slab must be allowed to dissipate. Insulation of the slab edge is important in cooler climates, to prevent warmth escaping through the edges of the slab. This insulation needs to be designed to complement the footing design, and should be undertaken in consultation with a structural engineer.

Acoustics need to be considered. Generally concrete slabs are a great way to reduce music or conversation noise being transferred from one level of a home to another, and between rooms on the same level. These noises will not be transmitted through a slab.

For the thermal mass of a concrete slab to work effectively, it must be able to interact with the house interior. Covering the slab with finishes that insulate, such as carpet, will reduce the effectiveness of the thermal mass. However, a wide variety of finishes are available that allow thermal mass to be utilised: Choices include ceramic tiles, slate tiles, terracotta tiles, pavers and bricks.