EPS waffle pods are more than efficient void formers – they also provide measurable thermal resistance beneath the concrete slab. Published research places this contribution at R0.57 to R0.65, depending on pod depth. A 7-star rating is achieved through the combined performance of the entire home, but EPS waffle pods give the floor system a valuable thermal head start. This page explains what the pods contribute, what additional floor insulation may be required, and how the complete system works together to support a comfortable, energy-efficient home.
What NCC 2022 requires
NCC 2022 lifted the minimum thermal performance standard for most new homes from 6 to 7 stars under the Nationwide House Energy Rating Scheme (NatHERS). It also introduced a separate Whole of Home assessment, which considers energy used by fixed services and appliances, together with any energy generated on site.
Implementation was staged across Australia. The higher BASIX standards commenced in New South Wales on 1 October 2023. The Australian Capital Territory introduced the new energy-efficiency provisions on 15 January 2024, followed by Victoria and Queensland on 1 May 2024. Because local variations and transitional arrangements applied, builders should always confirm the requirements for their jurisdiction and approval pathway.
For a waffle pod slab, the practical message is clear: the floor forms part of the home’s thermal envelope and can influence the NatHERS result. It should not be treated as thermally neutral. EPS waffle pods provide measurable thermal resistance beneath the concrete slab, helping the overall design work towards the 7-star target.
What a waffle pod slab contributes
CSIRO investigated the thermal resistance of waffle pod slabs and published additional R-values by pod depth, measured against a conventional 100mm slab on ground. These are the figures NatHERS assessors work from.
| Pod depth | Additional R-value | StyroPod® size | Site class under AS 2870 |
|---|---|---|---|
| 170mm | R0.57 | 150mm, set-downs | Shower and garage set-downs |
| 230mm | R0.60 | 225mm | Class M, moderately reactive |
| 300mm | R0.63 | 300mm | Class H, highly reactive |
| 370mm | R0.65 | 375mm | Class E, extremely reactive |
What this table means:
The published R-value represents the complete slab system. It measures the additional thermal resistance delivered by the waffle pod slab as constructed, not simply the material R-value of EPS in isolation. For NatHERS modelling, the relevant figure is the system contribution: R0.57 to R0.65, depending on pod depth.
The thermal benefit is built into a structurally driven design. Pod depth is determined by the site classification under AS 2870-2011 and the engineer’s slab design; it is not selected as an energy-rating upgrade. A Class E site may require a 375mm pod because of the soil conditions, while a Class M site may use a 225mm pod. The difference in R-value is a consequence of the structural specification, not a reason to select a deeper pod.
The important point is that, whichever pod depth the engineer specifies, an EPS waffle pod slab makes a real and measurable contribution to the floor’s thermal performance. That benefit is already built into the slab system; it does not need to be added as a separate feature.
How a waffle pod slab manages heat flow
Heat moves through a slab-on-ground floor by two main paths: downward through the underside of the slab and outward through its exposed perimeter.
EPS waffle pods address the first path by providing measurable thermal resistance beneath the concrete. Where additional performance is required, slab-edge insulation complements the pods by reducing heat flow through the perimeter. This is not a limitation of EPS waffle pods – it reflects how heat moves through any slab-on-ground floor.
Because the pods and slab-edge insulation address different heat paths, their R-values cannot simply be added together. For example, a pod contribution of R0.60 and a slab-edge board rated at R0.94 do not create a floor rated at R1.54. NatHERS assesses the underside and perimeter contributions separately.
Used together, EPS waffle pods and appropriately specified slab-edge insulation provide a more complete thermal strategy: the pods reduce downward heat flow, while the edge insulation addresses perimeter losses. This allows the waffle pod slab to make a stronger contribution towards the home’s overall 7-star result.
Slab-edge insulation: completing the floor system
Once the EPS waffle pods have reduced heat flow beneath a waffle pod slab, slab-edge insulation can address the exposed perimeter. It consists of rigid insulation board installed vertically against the outer edge of the concrete, either before or during the pour, depending on the specified construction detail.
StyroTherm XPS is manufactured for this application. Its compressive strength helps it withstand backfilling, while its closed-cell structure provides resistance to moisture in ground-contact applications. Depending on thickness, its thermal resistance ranges from R0.94 at 30mm to R2.15 at 75mm.
StyroTherm is also manufactured using up to 90 per cent recycled polystyrene recovered from EPS packaging, adding thermal performance while keeping valuable material in productive use.
Where the design requires even greater floor performance, high-density StyroSheet EPS or StyroTherm XPS can be installed beneath the slab as a continuous insulation layer. This is a separate construction detail that can affect the vapour barrier, penetrations and pour sequence. It should therefore be coordinated with the engineer and NatHERS assessor from the beginning rather than introduced late in the project.
Together, these options provide a flexible thermal strategy: EPS waffle pods beneath the concrete slab, StyroTherm XPS around the perimeter and continuous under-slab insulation where the modelling requires it.
Specifying a concrete slab as one system
A 7-star rating is achieved across the whole home, but the floor should be designed as one coordinated system. The EPS waffle pods, slab-edge insulation and, where required, continuous under-slab insulation each address a different part of the floor’s thermal performance.
Foamex manufactures all three components in Australia. This allows the complete waffle pod slab insulation system to be quoted through one supplier, with product selection, construction details and delivery coordinated together rather than resolved separately.
StyroPod® waffle pods are manufactured to AS 1366.3 and contain recycled material. StyroTherm® slab-edge and under-slab boards are manufactured using up to 90 per cent recycled polystyrene recovered from EPS packaging. StyroSheet EPS boards are also manufactured to AS 1366.3, with flame-retardant properties incorporated into the raw-material formulation.
The result is a locally manufactured and coordinated floor system that combines structural requirements, measurable thermal performance and recycled material content.
Talk to Foamex about the floor as a whole. We manufacture the pods, the slab edge and the under slab boards, and we can work through the details with your engineer or energy assessor.
Frequently asked questions
Do waffle pods count towards a NatHERS rating?
Yes. A waffle pod slab is modelled as a concrete top layer with an additional insulation layer beneath it, at R0.57 to R0.65 depending on pod depth.
Will a waffle pod slab get my house to 7 stars on its own?
No. The pods contribute to the floor, but a 7 star result depends on the whole envelope, and within the floor the slab perimeter has to be addressed separately.
What R-value does a 300mm waffle pod add?
R0.63 as an additional insulation layer, based on CSIRO testing of a 300mm pod against a conventional 100mm slab on ground.
Can I choose a deeper pod to improve my rating?
Pod depth is determined by the site classification under AS 2870-2011 and the engineer’s slab design, not by the energy rating. The difference between the shallowest and deepest pod is 0.08 in additional R-value.
Is slab edge insulation required under NCC 2022?
Requirements vary by jurisdiction and by the compliance pathway used. Where a floor needs to contribute more, slab edge insulation is usually the most direct way to get it, because perimeter loss is concentrated and treatable.
Sources
- Thermal resistance figures: CSIRO Australian Housing Data, thermal resistance of waffle pod slabs.
- Star rating requirement and adoption dates: Nationwide House Energy Rating Scheme, NatHERS.
- Site classification: AS 2870-2011, Residential slabs and footings.
- Moulded EPS: AS 1366.3, Rigid cellular plastics sheets for thermal insulation.