Case study 01 · Residential · Class 1a · Performance Solution
A two-storey, lightweight steel-framed townhouse in Currambine, WA, with R2.0 batts in its walls, R5.0 in its ceiling and single-glazed, clear windows in aluminium frames. Rated under NatHERS, it would have needed extensive insulation and glazing upgrades, and changes to its design. Verified as a Performance Solution under H6V2, it complied as drawn.
01The frame
The townhouse in layers: its structure (the steel frame to the manufacturer’s specification, the garage’s brickwork, laid brick by brick, and the slabs), its insulation, each product in its own colour, and its glazing, by type. Turn each layer on or off to see it on its own, or show the complete house, and switch between the two routes to see what NatHERS needed, in place. Turn the model, take it apart storey by storey, and point at any part, or any line of the key, to see what it is.
02The outcome
Both pathways ask the same question: will the house keep its heating and cooling within the NCC’s limits? A NatHERS rating answers it against a fixed star band. H6V2 answers it against the Code’s reference version of the same house, built to the Deemed-to-Satisfy Provisions. For this steel-framed townhouse, that difference decided whether it could be built as drawn.
Deemed-to-Satisfy · 7 stars
What it needed
Complied only with upgrades
Verified under H6V2
What it needed
Complied as drawn
H6V2’s two tests: the proposed house against the reference, each no more than 100%
Heating load
80%of the referencePass
5.36 kWh/m² proposed6.69 kWh/m² reference
Cooling load
92%of the referencePass
12.97 kWh/m² proposed14.17 kWh/m² reference
Heating and cooling together: 88% of the reference, 18.33 kWh/m² proposed against 20.86 kWh/m²
03The site and its climate
The street is to the south-south-east, the rear lane to the north-north-west. Living areas open on to a courtyard facing north-north-west, with the garage and laundry across it on the lane.
The climate · NatHERS zone 52, Swanbourne
04How they compare
Where the two differ, then what they share. Select a value to see it in the 3D model.
| Element | NatHERS | Performance Solution |
|---|---|---|
| Insulation | ||
| Ceiling | R6.0 batts | R5.0 batts |
| External walls | R2.5 batts | R2.0 batts |
| Internal walls | R2.5 batts | R2.0 batts |
| Glazing | ||
| Awning windows | Double glazed, low‑EU 3.95 · SHGC 0.47 | Single glazed, 4 mm clearU 6.57 · SHGC 0.63 |
| Fixed windows | Double glazed, low‑EU 2.91 · SHGC 0.54 | Single glazed, 4 mm clearU 6.45 · SHGC 0.78 |
| Louvre windows | Single glazed, low‑EU 4.36 · SHGC 0.57 | Single glazed, 4 mm clearU 5.98 · SHGC 0.67 |
| Sliding doors | Double glazed, low‑EU 3.50 · SHGC 0.51 | Single glazed, 5 mm clearU 6.12 · SHGC 0.70 |
| Hinged doors | Double glazed, low‑EU 3.80 · SHGC 0.48 | Single glazed, 5 mm clearU 6.03 · SHGC 0.59 |
| Design and specification | ||
| Window frames | Lighter colour, solar absorptance 0.50 | Charcoal Lustre, solar absorptance 0.69Home owner’s preference |
| Floor coverings | Tiles throughout the ground floor | Tiles and carpet on the ground floorHome owner’s preference |
| Ceiling fans | 1200 mm diameter fans in all four bedrooms, and one in the kitchen, living and dining | NoneHome owner’s preference |
| The same in both | ||
| Frame | Steel, 0.75 mm BMT | |
| Roof | R1.3 blanket | |
| Upper floor | R2.0 batts and 75 mm EPS, where over outside air | |
| Slab | Uninsulated | |
05How it was verified
A performance-based design brief, agreed with the building surveyor before any modelling: the Performance Requirement, H6P1, the Verification Method, H6V2, and the inputs both models share.
The design as drawn, run hour by hour through the 8,760 hours of NatHERS climate zone 52’s typical year. Its steel frame’s thermal bridging was modelled as the NCC requires.
The same house, built to the Deemed-to-Satisfy Provisions of Parts 13.2, 13.3 and 13.5, run the same way through the same year.
The proposed house’s heating load and its cooling load must each be no more than the reference house’s. Both passed.
The method, inputs and results, written up for the registered building surveyor, who approved the Performance Solution and issued the Certificate of Design Compliance.
06Credits and notes
The 3D model is drawn from Plunkett Homes’ working drawings and Centurion Framing Systems’ specification, used with permission. Its members are laid out from the drawings, so their exact positions are indicative. The floor trusses are drawn at assumed centres until their specification is supplied, and the garage’s steel beam at the size its detail draws until the engineer’s is.
Disclosure: Thermarate and Centurion Framing Systems have worked together occasionally, with no formal arrangement.
The map shows the suburb only, for the owner’s privacy.
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