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Waffle Slab Foundation vs. Reinforced Slab Foundation

Waffle slab is a re-invention of an old idea in the modern world. Slab foundations are a lot more common we see them when we: walk on the sidewalk, drive on the roads, or go down in our basements. So, how does one stack up against the other, and which one is better? There are pros and cons of each which you should consider when choosing your next house or garage foundation.

A waffle slab foundation is a type of foundation which is laid on grade and poured over interconnected boxes, which once done give the impression of a waffle pattern as can be seen in Figure 1. The benefits of such a system are its very effective when places on expansive soils. Expansive soils such as smectite clays are soils which swell when they absorb water. This causes an uplift force and can lead to uneven floors and cracks as the floor starts to shift under a regular slab. With a waffle slab though the soil fills in the crevices between the vertical reinforcement sections. This means that the house’s foundation is capable of absorbing volume. It also saves on time since no excavation is required and no engineering fill is required. Some cons of a waffle slab foundation are it’s not very useful on the soft ground since it sinks in and would require extra bored holes and piers for support. Waffle slabs use a special form which is placed and have concrete poured over them. This though limits their height to 375mm max. Pouring footings for slabs can be any depth up to 475mm and if you choose to place a grade beam then the possibilities are almost endless. Another issue is since the waffle slab lies on the ground houses constructed in this manner don’t do well in high wind or cyclonic areas. When high winds blow along a house’s roof, it creates uplift pressure which could cause deformation of the slab and damage to it.

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