Advantages of waffle pod slab foundation of home?

Answer 1

There is only one advantage of waffle pod slab construction - reduced cost. The waffle pod slab is no more than a slab of concrete placed on the ground, with polystyrene blocks in a grid pattern within. This results in a system consisting of a slab with a grid of stiffening and edge beams, giving the (reverse) effect of a 'waffle' if viewed from underneath.

If construction is to take place on reactive soil, consideration needs to be given to the future maintenance of the slab. There is some requirement to ensure consistency in the landscaping and general treatment of the areas surrounding the slab. Typically, having concrete on one side, for example a driveway, gardens on another side, perhaps gravel on a third side and a timber deck on the fourth side can result in different soil moisture conditions which in turn can lead to structural movement and failure. Of course it is difficult to regulate the area underneath the slab.

Builders often advise that consistent landscaping or even a concrete apron around the house is required to ensure reliable performance of the slab, unfortunately this advice is sometimes given when it is too late. Typically, category 1, 2 and sometimes category 3 cracks appear, and when the builder is advised he engages an engineer (usually the engineer who designed the slap) to give an opinion. Invariably, it seems to be the fault of the owner.

The problem is that houses commonly have concrete on one side (the driveway) and gardens or lawn on another side, so the question really is, is it acceptable that the slab and foundation material be so fragile? Usually, stable foundation material will be found at a reasonable depth - perhaps 600mm - 1200mm. Home builders should obtain a quote for the price difference between a waffle pod slab and a conventional slab & beam construction, keeping in mind the cost of rectification in a cracking building and the effect on resale value.

Builders should advise their clients accordingly and give them the option. At the moment, clients are not given the option, the display homes they are shown are not cracked, the brochures do not warn of the likelihood of cracking, they are not told of the onerous maintenance requirements, and it is not until it is too late that the issue arises.