What is a waffle pod slab?
Waffle slab is mainly a cost-effective structural element in the building that also has some energy cost savings benefits. It consists of edge footings and narrow internal strip footings. It is built on the ground and 170 to 370mm polystyrene waffle pods fill the voids between the strips. The polystyrene in the waffle pods and air pockets built into the pods provides insulation to the floor which can assist with NCC energy compliance and 6-star energy rating.
What is the thermal benefit of using a waffle pod slab in energy rating?
The use of an almost 200mm waffle pod and unventilated air pockets in it, provides an insulating effect under the building floor. In heating dominant buildings, the extra insulation effect of the waffle pod slab assists with better energy compliance of the building at lower construction cost.
What is the equivalent R-value of waffle pods?
Referring to the research by CSIRO, the following insulation values are recommended for the waffle pod slabs:
- Waffle pod height: 170mm – R0.57
- Waffle pod height: 230mm – R0.6
- Waffle pod height: 300mm – R0.63
- Waffle pod height: 370mm – R0.65
Note that in the above, the waffle pod is assumed to be composed of 50mm polystyrene layers and an un-ventilated air pocket. Note that increasing the waffle pod height doesn’t add much to the insulation effect. Double the waffle pod height increases the added insulation value of the waffle pod by 14%.
The waffle pod slabs may be modelled by using a concrete top layer at the specified concrete thickness of the waffle pod slab system with an additional insulation layer of R0.57, R0.60, R0.63 and R0.65 for the 170mm, 230mm, 300mm and 370mm pod heights between the concrete top layer and the ground.
The following shows an example of a waffle pod in one of our Energy Compliance reports:
The disadvantage of waffle pods in building energy efficiency
The addition of insulation by waffle pods disconnects the ground thermal mass from concrete thermal mass. This means that the use of a waffle slab in a cold climate reduces the thermal mass of the floor, hence less energy is stored during the day.
Section J-JV3 modelling (Verification Using Reference Building)