Concrete foundations – a look at the trends

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In recent years concrete slab foundations have become increasingly popular owing to their speed of construction and relative economy, compared with the use of traditional piles and foundation walls.

The standard for the construction of a concrete slab is to be found in NZS 3604.

Durability is covered in Section 4.8 where the minimum cover to steel and minimum strength measured in MPa after a given number of days is described. Mention is also made of NZS 4210, which covers materials and workmanship.

The design and construction of concrete slabs is covered in Section 7.5.

However, one characteristic of concrete slabs that will become important in the near future will be the need to properly insulate the slab. This is because concrete has only a minor degree of insulation itself, though it does have excellent thermal mass (storage).

As Building Code requirements improve for the overall insulation of dwellings, so the requirement for better insulation from floors will be improved as well.

Currently there are few systems available for insulating slab on ground foundations. Many use the thermal insulation properties of expanded polystyrene as a means of improving the insulation properties of the concrete slab.

However, as has been identified by research, it is just as important to insulate the perimeter of the slab as it is to insulate the slab from the ground underneath.

Overseas there is considerable research being undertaken into developing pourable concretes with improved insulation properties. Typically, the concrete with such insulation tends to be weaker and require strength improvers, which adds to the cost.

Trials using naturally occurring insulants such as Zeolite have been carried out in New Zealand with limited success. More research is needed to enable builders and concrete placers to provide a sufficiently insulated slab on ground that will meet the new Building Code Requirements.

Watch this space for developments concerning slabs on ground.

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