Double Glazing Requirements Under NCC 2022 Energy Provisions

What This Requirement Covers

Double glazing under the NCC 2022 energy provisions refers to the use of multi-pane glazing systems (typically two or more glass panes separated by an air or gas-filled cavity) to improve thermal performance of wall-glazing construction. The NCC treats glazing performance as part of the building fabric energy requirements by controlling both heat flow (U-value) and solar heat gain (measured as SHGC or solar admittance). These controls exist to reduce space-heating and cooling loads, improve occupant comfort, and lower whole-of-life energy use for buildings across all classes in Australia.

The requirements apply to designers, builders, certifiers and manufacturers when specifying or installing glazing in external walls, curtain walls, and other wall-glazing constructions that form part of the external building fabric. The rules are incorporated into NCC Volume One energy provisions (Specification 37 and the J4D6/J3D9 performance limits), and interact with state schedules where local variations exist.

Key Requirements

1. Total System U-Value limits: The Total System U-Value of a wall-glazing construction must be calculated in accordance with Specification 37 (S37C3 and S37C4) as the area-weighted average of component Total System U-Values including thermal bridging and must not exceed the applicable value in J4D6(1). For sole-occupancy units in Class 2 and Class 4 parts, NSW adds J3D9 specifying U-limits for climate zones: U2.2 (zones 1-5), U2.0 (zone 6), U1.4 (zones 7-8) as Total System U-Value caps (see J3D9(1)).
2. Solar admittance / SHGC controls: The solar admittance (or equivalent Total System SHGC for glazing) of externally facing wall-glazing construction must not exceed the values specified in Table J4D6b (for Class 2 common areas, Class 5-9b, and Class 9a non-ward) or Table J4D6c (for Class 3, Class 9c, and Class 9a ward areas). Calculation method for solar admittance is in Specification 37 (S37C6 and S37C5). For display glazing the Total System SHGC must not exceed 0.81 divided by the applicable shading factor specified in S37C7 (see J4D6(7)).
3. Method and calculation references: Use S37C3 (U-Value Method 1 single aspect) and S37C4 (U-Value Method 2 multiple aspects) to calculate U-values; use S37C5 (Total System SHGC and solar admittance calculation) and S37C6 (solar admittance - Method 2 multiple aspects) for solar admittance. Permanent external shading and shading factors are measured in accordance with Figure S37C7 and S37C7 text.
4. Minimum wall R-values where wall forms significant proportion: Where the opaque wall is 80% or more of the wall-glazing construction area, the opaque wall must meet the minimum Total R-Value specified in Table J4D6a (see J4D6(4)). Specific values are climate-zone dependent and provided in Table J4D6a in NCC Volume One.
5. Specific numeric examples and thresholds:
6. 80% rule: If the opaque wall area ≥ 80% of wall-glazing construction, apply Table J4D6a wall R-value minima (J4D6(4)).
7. Display glazing SHGC cap: Total System SHGC ≤ 0.81 / shading factor (J4D6(7)).
8. NSW sole-occupancy U-limits: U2.2, U2.0, U1.4 depending on climate zone as per J3D9(1).
9. Standards and calculation references:
10. U-value and material R-values in Specification 37 are to be determined using AS/NZS 4859.2 or Specification 38 for spandrel panels (S37C3(2)).
11. Use Specification 37 for methods to derive Total System U-Value, SHGC and solar admittance (S37C1-S37C7).
12. Applicable building classes: Requirements apply across building classes where external wall-glazing construction forms part of the external fabric, specifically referenced across Class 1 (where relevant in Volume Two and state schedules), Class 2 common areas and sole-occupancy units, and Class 3-9 buildings as listed in J4D6, Tables J4D6b and J4D6c.
13. Citations: See NCC 2022 Volume One, Specification 37 (S37C1-S37C7) and J4D6/J3D9 clauses and tables for climate-zone dependent numeric limits.

Residential vs Commercial

1. Residential (Class 1 and Class 2 sole-occupancy units): In Volume Two and state schedules, glazing energy controls are implemented for housing; for Class 2 sole-occupancy units NSW J3D9 explicitly applies Total System U-Value caps by climate zone (U2.2, U2.0, U1.4). Class 1 detached housing is primarily covered by NCC Volume Two energy provisions (refer to Volume Two Section 3 and Section 6 as applicable) but the same calculation methods for glazing performance (Total System U-Value and SHGC) and Specification 37 principles inform performance solutions.
2. Commercial (Class 2 common areas and Class 3-9): The NCC Volume One performance limits in J4D6b and J4D6c set maximum solar admittance values and U-value caps for wall-glazing construction in non-residential buildings. Class 2 common areas and Class 5-9b buildings use Table J4D6b; Class 3 and certain health-care or aged-care areas use Table J4D6c, which may have different (often more restrictive) solar admittance limits due to occupant sensitivity or function.
3. Practical difference: Commercial façades, curtain walls and large display glazing often face stricter combined SHGC/admittance and shading-factor calculations (including display glazing specific cap of 0.81/shading factor) and must use the multi-aspect methods (S37C4/S37C6) for large or multi-aspect façades.

Exceptions and Exemptions

1. Opaque-wall-dominant assemblies: Where the opaque wall is 80% or more of the wall-glazing construction area, different R-value minima from Table J4D6a apply rather than the glazing-dominated limits (J4D6(4)).
2. Internal glazing: Wall-glazing construction that is wholly internal (not externally facing) is excluded from external solar admittance limits (J4D6(5) excludes wholly internal wall-glazing construction).
3. Display glazing alternative calculation: Display glazing has a specific cap (Total System SHGC ≤ 0.81 / shading factor) which provides an alternative numeric constraint to ordinary solar admittance limits (J4D6(7)).
4. Performance solutions: Where deemed-to-satisfy provisions cannot be met, a performance solution may be proposed demonstrating equivalent or better energy performance. Such solutions must follow NCC performance pathways and reference Specification 37 calculation methods for verification.
5. State schedule modifications: State and territory schedules can modify or add provisions (for example NSW J3D9). Where a state schedule provides alternate values or requirements those apply in that jurisdiction.

State and Territory Variations

1. New South Wales (example): NSW includes J3D9 for wall-glazing construction of sole-occupancy units of a Class 2 building or a Class 4 part, with explicit Total System U-Value limits by climate zone (U2.2, U2.0, U1.4) and further solar admittance or SHGC provisions in J3D9(4)-(6). See NCC 2022 Volume One, J3D9 for full text.
2. Other states and territories: The NCC requires checking the relevant state schedules in Volume One (Schedules 4-12) because local schedules may alter numeric limits or add requirements. Common variations can include climate-zone mapping nuances, minimum R-values for opaque walls, or additional glazing energy requirements for particular building types. Always verify against the applicable state schedule in NCC 2022 Volume One.

Practical Compliance Tips

1. Calculate using Specification 37: Always calculate Total System U-Value and solar admittance using Specification 37 (S37C3-S37C6) and document the inputs (glass type, cavity gas, spacer, frame thermal break, shading factor) so a certifier can verify results.
2. Use certified product data: Obtain SHGC and U-value data from tested and certified product literature for double-glazed units (including spacer, edge-seal and gas fill). Avoid relying on generic single-pane numbers.
3. Check the 80% rule early: Determine whether opaque wall area ≥ 80% of wall-glazing construction early in design, as this changes which R-value minima or limits apply (J4D6(4)).
4. Account for frames and thermal bridging: Frame area, material and thermal breaks materially affect Total System U-Value. Include frame U-values and thermal bridging allowances per AS/NZS 4859.2 and Specification 37 calculations.
5. Model shading accurately: Permanent external shading (P, G, H in Figure S37C7) directly changes allowable SHGC/admittance. Measure and document shading projections to apply the correct shading multiplier from S37C7.
6. Don’t forget display glazing rules: For shopfronts or display glazing use the specific cap: Total System SHGC ≤ 0.81 / shading factor (J4D6(7)) and provide shading factor calculations where applicable.
7. Refer to state schedules and J3D9 where applicable: Before finalising compliance documentation, verify state schedule clauses (e.g., NSW J3D9) that may impose different Total System U-Value or SHGC limits for residential sole-occupancy units.

Cited references: NCC 2022 Volume One - Specification 37 (S37C1-S37C7), J4D6 (Tables J4D6a, J4D6b, J4D6c) and NSW schedule J3D9. Also use AS/NZS 4859.2 where material thermal properties are required and Specification 38 for spandrel panels where relevant.

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