A ‘Waffle Pod’ slab is now probably the most common Concrete ‘Raft’ House base. Its generally taken over from the Conventional Raft Foundation.
It’s an example of composite construction with polystyrene pods forming voids in the underside of the concrete ‘Waffle’.
This photo shows the pods, with the reinforcement placed over them, prior to placing the concrete.
- No trenches resulting in:
- Simpler excavation; and
- Flat site means site is easier to keep dry than trenches that collect water.
- Waffle Pods bring house further out of ground. In an area that is wet the higher the better.
- Better insulation from the ground meaning the floor will warm up quickly from cold. (especially if you go for in slab heating)
- More susceptible to bad workmanship – If the pods move during placing of the concrete.
- More susceptible to bad drainage which can lead to soil heave if building on reactive clay
- Lower thermal mass so less suited to passive solar design.
- Thinner slab (typically 75mm rather than 100mm) means may not be as resistant to point loads such as jacking a car. Some people specify 100mm thickness for garage floor.
- A thicker overall slab may be needed if you want Floor Drains (To allow for the dropped floor in those rooms)
If your block has difficult ground conditions its still possible to use a waffle pod slab with:
Also see Ground Conditions