Waffle pod slabs are a solution engineers devised in response to difficult soil conditions.
They are typically used in areas of highly reactive clay soils. (See soil types H1 and H2)
Such soils move anything sitting on them (including house footings) as they swell and shrink.
Reactive soil is sponge like, expanding with the influx of ground water and shrinking during dry periods.
Such movement can cause serious cracking to standard concrete strip footings and pads. It is not unusual for such affected footings to move up and down, as much as 40 to 60mm
“Class H” soil, that is a heavy clay is expected to move some 40 to 60mm at the surface under normal seasonal conditions – that is without any significant extraneous influences.” Irwin Structures
For illustrative purposes only; see Norfoam Cool Solutions Waffle Pods
Waffle pod Slabs are a Raft Slab with extra reinforcement (ribs) which, float like a raft. It should move, as a whole, up and down without major cracking and failure. In particularly difficult soil conditions, Waffle Slabs may include coupled, deeper piers as well.
Providing such slabs are correctly designed they should perform well even to the extent of providing sufficient bearing for ground floor extensions and second story additions.
The most important thing an extension builder needs in this situation is the original engineering design drawings and computations. This information provides the engineer designing the new extension structural, where to apply their design loads.
The original Builder and or the local council should be able to provide the original engineering slab design documentation.
If you are looking to extend on to a Waffle Slab, call Capital Building.
We have extensive experience in this area and we work with qualified engineers who understand the issues. Call today on 9857 9200 and book a free consultation.