Window-to-Wall Ratio Energy Efficiency Requirements

What This Requirement Covers

Window-to-wall ratio (WWR) energy efficiency requirements govern how much glazing (windows and other glazed elements) may form part of an external wall assembly for the purpose of meeting the National Construction Code (NCC) energy efficiency objectives. These requirements exist to limit unwanted solar heat gain and reduce cooling and heating loads, while permitting adequate daylight and views. They apply where glazed elements form part of the external fabric of a building and are assessed as part of the wall-glazing construction under the NCC energy provisions.

The rules apply across building classes covered by the NCC, but the test method and allowable limits differ by building class, climate zone, orientation and whether the glazing forms part of a sole-occupancy unit, common area or other building type. The NCC expresses limits through maximum allowable solar admittance, area-weighted Total System U-Value, and minimum Total System SHGC requirements in some locations, rather than a single “percentage WWR” number; the wall-glazing construction area and its components are used in calculations in Specification 37 to determine compliance. Relevant references include NCC Volume One (energy provisions and Specification 37), NCC Volume Two and the ABCB Housing Provisions (Deemed-to-Satisfy glazing provisions for Class 1 and 10), plus applicable Australian Standards such as AS 2047 and AS 1288 for window and glazing design.

Key Requirements

1. The NCC treats glazing as part of the wall-glazing construction and requires calculation of a representative performance using Specification 37. See NCC Volume One, Specification 37 - Calculation of U-Value and solar admittance and S37C5 - S37C7 for calculation methods and shading multipliers.
2. Solar admittance of externally facing wall-glazing construction must not exceed the values specified in J4D6(5) (Table J4D6b / J4D6c) depending on building class and climate zone - see NCC Volume One, J4D6(5). The solar admittance is calculated in accordance with Specification 37 (S37C5, S37C6). Exact values vary by climate zone and aspect; for example Table J4D6b lists maximum solar admittance values by climate zone and aspect for Class 2 common areas and Class 5-9b buildings (refer to NCC Volume One, Table J4D6b).
3. The Total System U-Value of wall-glazing construction (area-weighted average of component U-values) must not exceed the applicable limits in J4D6(1) - calculated in accordance with Specification 37 (NCC Volume One, J4D6(1) and related clauses). Example NSW requirement: for sole-occupancy units of Class 2 or a Class 4 part, Total System U-Value limits are U2.2 (climate zones 1-5), U2.0 (zone 6) and U1.4 (zones 7-8) - see NSW J3D9(1) (NCC Volume One).
4. For some building types and climate zones the NCC prescribes minimum glazing SHGC or limits on Total System SHGC for display glazing (e.g., Total system SHGC of display glazing must not be greater than 0.81 divided by the shading factor in S37C7) (NCC Volume One, S37C5(7)). In climate zones 7 and 8 some clauses require glazing to have a Total System SHGC of at least 0.4 for particular wall-glazing construction (see NSW J3D9(5)).
5. For Class 1 and 10 (housing), glazing must meet the ABCB Housing Provisions Part 8 (windows and glass) or, where applicable, AS 1288 and AS 2047 for design, testing and installation. See NCC Volume Two, H1D5 and ABCB Housing Provisions Part 8. Refer to NCC Volume Two H2D7 and related ABCB Housing Provisions references for glazing weatherproofing and design requirements.
6. Calculation details and the definition of wall-glazing construction area components (wall, glazing elements, spandrels etc.) and the weighting for multiple-aspect façades are set out in Specification 37 (NCC Volume One, Specification 37; S37C5-S37C7). The solar admittance calculation uses glazing area, shading multipliers and SHGC values and then compares the representative value to the applicable reference value in J4D6(5).
7. Window and glazing design/strength/human impact requirements are cited to AS 2047 (windows), AS 1288 (glass in buildings) and other standards as required by NCC Volume Two and ABCB Housing Provisions (NCC Volume Two H1D5; ABCB Housing Provisions Part 8; NCC Volume Two H2D7).

Residential vs Commercial

1. Residential (Class 1 & 10 and Class 2 sole-occupancy units):
2. - For Class 1 houses and Class 10 structures, the ABCB Housing Provisions Part 8 supplies Deemed-to-Satisfy glazing provisions, and NCC Volume Two cross-references those provisions for weatherproofing and glazing design (NCC Volume Two, H2D7; ABCB Housing Provisions Part 8).
3. - For multi-unit residential sole-occupancy units (Class 2 S O U), NCC Volume One contains specific limits for wall-glazing construction U-Value and solar admittance (see NSW J3D9 as an example for sole-occupancy units; similar national clauses in J4D6 apply for common areas and Class 3/9c/9a wards). For sole-occupancy units the Total System U-Value limits can be tighter (e.g., U2.2 / U2.0 / U1.4 depending on climate zone per NSW J3D9(1)).
4. Commercial (Class 2 common areas, Class 3-9):
5. - The NCC Volume One energy provisions apply through J4D6 and Specification 37; commercial and higher-occupancy buildings are assessed by maximum solar admittance and minimum wall Total R-Value where applicable. Table J4D6b and J4D6c give different allowable solar admittance values by climate zone and aspect for Class 2 common areas and Class 5-9b buildings versus Class 3/9c/9a ward areas (NCC Volume One, Table J4D6b / J4D6c).
6. - For many commercial buildings the compliance path is performance-based calculation of solar admittance and U-Value rather than a simple WWR cap; this means designers can trade off higher glazing area with lower SHGC glass, better shading, higher-performing frames and improved spandrel/wall thermal performance.

Exceptions and Exemptions

1. Where glazing is wholly internal (not externally facing), the solar admittance limits for externally facing wall-glazing construction do not apply (NCC Volume One, J4D6(5) note and S37C5(6)).
2. The ABCB Housing Provisions provide Deemed-to-Satisfy alternatives for many Class 1 and 10 glazing situations that, if followed, satisfy H1P1 and related performance requirements (ABCB Housing Provisions Part 8, NCC Volume Two references).
3. Certain special assemblies (skylights, rooflights, windows not in vertical plane, heritage or reused windows, revolving doors, and some frameless glazing) are treated separately in NCC Volume Two and ABCB Housing Provisions; they may need AS 1288 or AS 2047 compliance instead of the standard external wall glazing treatment (NCC Volume Two H1D5 and H2D7; ABCB Housing Provisions Part 8).
4. State or territory schedules in the NCC may replace or modify national values (see State and Territory Variations below) and may include local exemptions or stricter limits; always check the relevant schedule in NCC Volume One and Volume Two and the ABCB Housing Provisions schedules.

State and Territory Variations

1. The NCC includes state schedules that can modify national provisions. For example, New South Wales inserts specific tables and clauses (NSW J3D9) setting Total System U-Value limits and solar admittance tables for sole-occupancy units and other building types (NCC Volume One, NSW J3D9 and NSW J4D6 tables). The NSW schedule specifically inserts NSW J4D6a/b/c tables for maximum solar admittance by climate zone and aspect.
2. Other jurisdictions may adopt the national values or include their own amendments in the schedules to NCC Volume One or the ABCB Housing Provisions schedules-this can alter allowable solar admittance, minimum/maximum U-Values, or impose additional controls for bushfire-prone areas or local climatic considerations. Always verify against the state or territory schedule in NCC 2022 Volume One and the ABCB Housing Provisions schedules (NCC Volume One, Schedules 4-12; ABCB Housing Provisions Schedules).

Practical Compliance Tips

1. - Use Specification 37 early in design: calculate the wall-glazing construction solar admittance and Total System U-Value during schematic design so glazing area, SHGC, and shading strategies can be optimised to meet Table J4D6 limits. (See NCC Volume One, Specification 37; S37C5-S37C7.)
2. - Treat façades by aspect: the NCC allows aspect-weighted assessment (Method 2 S37C6) so split façades into aspects (N, E, S, W) and apply appropriate shading multipliers rather than relying on a single average.
3. - Combine passive measures: if you need larger glazing areas, offset higher WWR by reducing SHGC (low-e coatings), increasing external shading, or improving spandrel wall R-values - the performance method lets you trade glazing performance for area.
4. - Follow the housing provisions for Class 1/10: for houses, use ABCB Housing Provisions Part 8 and AS 2047/AS 1288 for window selection and installation to satisfy H1P1 and H2P2 without needing complex performance modelling.
5. - Check local schedules and NSW special limits: always confirm the applicable state schedule in NCC Volume One and the ABCB Housing Provisions schedules early - NSW, for example, sets explicit U-Value thresholds for sole-occupancy units (NCC Volume One, NSW J3D9).
6. - Use tested window data: select windows with certified Total System U-Value and SHGC data (AS 2047 test results) so Specification 37 inputs are robust and you avoid underestimating thermal performance.
7. - Document shading assumptions: if compliance relies on shading multipliers from S37C7, record the geometry, projection factors and any assumed fixed or operable shading devices so certifiers can verify the calculation inputs.

Sources cited in this article: NCC 2022 Volume One - Building Code of Australia (J4D6; Specification 37; S37C5-S37C7; NSW J3D9 and inserted tables), NCC 2022 Volume Two - Building Code of Australia (H1D5; H2D7), and ABCB Housing Provisions Standard 2022 (Part 8 glazing provisions).