Is double glazing required on a new SA house?

Does the NCC require double glazing?

The text of Part 13.3 External glazing in the NCC 2022 Housing Provisions does not use the words double glazing, single glazing or insulated glass units. It sets limits that a house’s glazing must meet as a whole, using two measured properties of each window: its Total System U-Value and its Total System SHGC.

Part 13.3 is part of the elemental Deemed-to-Satisfy route. Clause 13.3.1(2) says it “must be applied as directed in H6D2(1)(b)”, which is the list of Parts 13.2, 13.3, 13.4 and 13.5. The other Deemed-to-Satisfy route, under H6D2(1)(a), is an energy rating using house energy rating software of at least 7 stars, including the separate heating and cooling load limits, under S42C2(1)(a); lower figures in S42C2(1)(b) and (c) apply only in climate zones 1 and 2. A Performance Solution is also possible, with the relevant Performance Requirements determined under H6D1(2).

Neither South Australian schedule to NCC 2022 read for this note varies Part 13.3: the Housing Provisions schedule lists Parts 4.2, 9.2, 10.2 and 13.1, and the Volume Two schedule has no entry for Part H6. South Australia modifies Part H6 separately through Ministerial Building Standard MBS 007, including concessions set out in the 7 star note; the relevant authority assessing the building work confirms which provisions apply.

• Adelaide climate zone and insulation R-values

What do U-value and SHGC mean for windows?

The NCC Glossary defines Total System U-Value as “The thermal transmittance of the composite element allowing for the effect of any airspaces, thermal bridging and associated surface resistances, expressed in Wm-2K-1.” A lower figure means less heat passes through.

For Volume Two, Total System SHGC is “the fraction of incident irradiance on glazing or a roof light that adds heat to a building’s space.” Both figures cover the glass and the frame together. The explanatory information to clause 13.3.3 says they are measured under the Australian Fenestration Rating Council procedures, and that published values may be called “U Factor” or “Uw”.

The ABCB Housing energy efficiency handbook adds that “Window products and their thermal performance (Total U-Value and Total System SHGC) are available from the Window Energy Rating Scheme (WERS)”.

How does Part 13.3 check the windows in a house?

Clause 13.3.2 is the winter check. “In climate zones 2 to 8”, the ratio of conductance to solar heat gain of the glazing in each storey must not exceed the allowance in Table 13.3.2a, using a formula that multiplies each window’s area, U-Value and SHGC by factors for exposure, orientation, room type, storey, frame and floor.

Clause 13.3.3 is the summer check. “In climate zones 1 to 7”, the aggregate solar heat gain of the glazing in each storey must not exceed the floor area of the storey multiplied by a constant from Table 13.3.3a, which varies with climate zone, floor type and ventilation opening area, and in zone 5 with the type of wall. In both clauses the SHGC input is defined as the Total System SHGC for each glazing element, “not exceeding 0.7”, and the ABCB handbook puts it as: “The SHGC must not exceed 0.7 for any piece of glazing.” These are Deemed-to-Satisfy provisions of the elemental route; roof lights have their own limits in clause 13.2.4.

Adelaide is climate zone 5 in Table 3 of the Glossary, so both checks apply there. Where shading is needed to comply, clause 13.3.4 requires an external permanent projection such as eaves or a verandah, or an external shading device “capable of restricting at least 80% of the summer solar radiation”.

The handbook lists the factors added in NCC 2022, including the type of room, the number of levels, floor coverings, window openability and the solar absorptance of window frames. The ABCB publishes an NCC 2022 Volume Two glazing calculator to help apply Part 13.3.

What does the ABCB handbook say about double glazing?

In its tips for a design that passes winter but fails summer, the handbook says: “Adding double glazed windows will slightly improve summer performance”. It then says “The best approach in summer may be to use a hard floor surface on a slab floor like ceramic tiles (floating timber does not help)”, and that glazing with a lower SHGC, a deeper overhang or lighter coloured window frames “will also help in summer but may cause problems in winter.” It separately suggests increasing window openability.

For milder climates it says: “In milder climates e.g. climate zones 2, 4 and 5, single low-e (low-emittance) glazing can reduce solar heat gain in summer and provide just enough improvement to limit heat loss to ensure winter performance still passes.” That is a general example from guidance, not a clause, and it does not settle whether a particular house passes.

For designs with a large area of windows, the handbook suggests considering NatHERS or verification using a reference building, because those options “permit trading of lower performing windows against improving the performance of other parts of the building fabric.”

Do windows matter for a 7 star NatHERS rating?

NCC 2022 H6D2(1)(a) requires compliance with both S42C2 and S42C4(1) on the software route. In the NCC 2022 text, S42C4(1) lists insulation, thermal breaks, ceiling insulation loss, floor edge insulation and Part 13.4 building sealing, and does not list Part 13.3. The applicable South Australian modifications must also be checked.

Windows still count. NatHERS says a Star Rating “analyses climate zone, orientation, insulation, shading, window types and building materials and air leakage”, and that new homes “are assessed using floor plans and specifications before they are constructed.” The glazing specified is therefore part of the modelled design, and the 7 star note covers what happens if a window changes after the rating.

• 7 star energy rating in SA: NatHERS and Whole of Home

What about skylights and roof windows?

Roof lights are dealt with in Part 13.2, not 13.3; the Glossary definition of glazing for Section 13 includes “a window other than a roof light”. Clause 13.2.4 of the NCC 2022 Housing Provisions covers roof lights, “including any associated shaft and diffuser”, serving a habitable room or an interconnecting space such as a corridor or stairway. It limits their total area to not more than 5% of the floor area served, and requires the transparent and translucent elements to have a combined Total System SHGC from Table 13.2.4 and a Total System U-Value “not more than U3.9”. These are Deemed-to-Satisfy figures in clause 13.2.4 of the elemental route, not a U-value set for windows generally.

Which other window rules apply to a new house?

Energy efficiency is one set of window provisions among several. Glass at risk of human impact, the wind rating of windows, and natural light and ventilation are dealt with in other Parts of the NCC 2022 Housing Provisions, covered in separate notes.

The glazing chosen for a house is shown in the window schedule and specification, and the designer, energy assessor and relevant authority assessing the building work confirm how it meets the route used. This note quotes NCC 2022; the ABCB lists South Australia’s NCC 2025 adoption dates as “BCA: 1 May 2027” and “PCA: 1 May 2026”, and the relevant authority confirms which edition applies.

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