# NCC 2025 Facade Calculator: A Practical Guide to Compliance Victoria's adoption of the National Construction Code 2025 marks a meaningful shift in how energy efficiency is assessed for commercial facades. Among the more consequential changes is the introduction of Specification 37, which governs facade compliance for Class 3 through 9 buildings and underpins the tool commonly referred to as the Facade Calculator.
This article provides a working overview of Specification 37, explains how the Facade Calculator operates in practice, identifies the compliance levers available to designers and specifiers, and offers a worked example for a typical office building in Melbourne. The intent is not to replicate the code itself, but to give practitioners a clear sense of what the tool expects, where it tends to fail, and how to respond constructively when it does. **Access the tool here:** [NCC 2025: The Facade Calculator](https://files.betterbuilding.io/docs/ncc_2025_facade_calculator_v_1_0.html) (and save it in your browser) **Access the Docs here:** [NCC 2025: The Facade Calculator Documentation ](/user-guide/tools-and-plugins/ncc-2025-the-facade-calculator.md) {% hint style="info" %} This calculator is not legal or professional advice and at the risk of the user, as per the ABCB NCC 2022 notice and disclaimer. Better Building have thoroughly tested and reviewed all inputs, calculations and outputs in this tool. Any bugs or errors can be reported to [support@betterbuilding.io](/support-and-training.md). {% endhint %} *** ### What is Specification 37? Specification 37 is the energy efficiency provision within NCC 2025 that establishes compliance pathways for the external facades of commercial buildings. In other words, it's the facade calculator. It replaces and substantially updates the previous glazing and facade requirements, with a notable shift in emphasis: external shading is now treated as a primary design mechanism, rather than an optional enhancement. In practical terms, Specification 37 sets performance targets for two key metrics: * **Wall glazing U-value:** A measure of the rate of heat transfer through the combined wall and glazing assembly. Lower values indicate better thermal resistance. * **Solar admittance:** A measure of how much solar energy is transmitted through the facade into the conditioned space. This is influenced by both the glazing specification (specifically the Solar Heat Gain Coefficient, or SHGC) and the presence of external shading. Compliance is assessed against both targets. Failing either constitutes a non-compliant outcome, and, as will become apparent, solar admittance is by far the more demanding of the two for typical commercial facades. *** ### The Facade Calculator The Facade Calculator is a free software tool designed to evaluate compliance against Specification 37. Users define a set of project inputs and the tool returns a compliance result for each facade orientation, highlighting failures and providing the underlying equations for review. The key inputs are as follows: * **Climate zone:** Determines the applicable performance targets. Results vary considerably between Melbourne (zone 6), Brisbane (zone 2), and Hobart (zone 7), so it is important to select the correct zone before drawing any conclusions. * **Building class:** Selects the applicable compliance pathway. Class 5-9 (commercial offices, retail, public assembly) and Class 3-9c (residential components of mixed-use buildings) have different targets, and this distinction has a material impact on results. * **Wall area and orientation:** The physical dimensions of each facade being assessed. * **Window-to-wall ratio (WWR):** The proportion of the facade that is glazed. * **Glazing system specification:** Including the U-value and SHGC of the selected glazing product. * **Shading geometry:** The projection depth of any horizontal or vertical external shading elements. The tool supports loading and saving projects, allows inspection of the design equations used in each calculation, and produces an exportable compliance report. *** ### Building Class and Its Effect on Compliance Thresholds Before working through a facade design, it is worth understanding how sensitive the results are to building class selection. The difference between Class 5-9 and Class 3-9c is not subtle. As a baseline example: a Class 5 office building in Melbourne climate zone 6, with a 30% window-to-wall ratio and a reasonable mid-range glazing specification, will generally achieve compliance under Specification 37.
The same geometry and glazing specification applied to a Class 3-9c building will fail immediately.
This matters in practice because mixed-use developments are common, and the residential floors within a commercial project are subject to different and more demanding requirements. A compliance strategy that works for the office floors may not translate to the apartments above. *** ### Why 30% Window-to-Wall Ratio Is Not a Realistic Starting Point It is worth acknowledging directly that a 30% window-to-wall ratio, while code-compliant in some configurations, is not representative of how most commercial office buildings are currently designed. The contemporary Australian commercial market has normalised glazed facades in the 50-70% range, and in some cases higher. Curtain wall systems are standard. The aesthetic and leasing expectations that drive façade design have not moderated to align with what older energy codes might have preferred. Specification 37 does not require designers to abandon contemporary facade systems. But it does require that those facades be accompanied by a substantive shading strategy. This is the central message of NCC 2025 in this area: glazing area is permissible, but it must be appropriately managed. The Facade Calculator reflects this intent. At 50% window-to-wall ratio for a Class 5 office in Melbourne, without external shading and with a mid-range glazing specification, the tool will return a failure across all orientations. Both the wall glazing U-value target and the solar admittance target will typically be missed, and this is represented visually in the tool as a pink result indicator. *** ### A Worked Compliance Example: Class 5 Office, Melbourne, 50% WWR The following example walks through a compliance strategy for a reasonably typical scenario: a Class 5 commercial office building in Melbourne (climate zone 6) with a 50% window-to-wall ratio. #### Step 1: Establish the Baseline Begin with the building geometry and a representative glazing specification. A standard low-e double-glazed clear unit will typically return an SHGC in the range of 0.35 and a centre-of-glass U-value around 2.8. At 50% WWR with no shading, this will fail both targets under Specification 37.
#### Step 2: Optimise the Solar Heat Gain Coefficient The solar admittance target is addressed first, because it is the more restrictive constraint and because the SHGC has a hard floor defined by what the glazing market can actually supply. There is no value in designing to an SHGC that cannot be procured.
For a triple low-e glazing system, an SHGC of approximately 0.26 is achievable and commercially available. This represents a significant reduction in solar transmission compared to low-e double-glazed clear, and it forms the foundation of a viable compliance strategy. Reduce the SHGC to this level before adding shading, so that the required shading depth is minimised. #### Step 3: Apply External Horizontal Shading With the SHGC reduced, the next step is to add external horizontal shading. Specification 37 places considerable weight on external shading as a compliance mechanism, and the calculator will reflect this in the results. For the scenario described above, a horizontal shading projection of approximately 300mm above each glazed panel will typically be sufficient to achieve the solar admittance target on the affected orientations. This applies to all facades in the model. The south facade is not a significant contributor to solar heat gain in Melbourne, but the simplified compliance model does not distinguish between orientations in the way that a detailed simulation would. For the purposes of the calculator, applying a consistent shading depth across all facades is an acceptable approach.
Vertical shading elements can also be specified within the tool, and they are worth investigating in specific circumstances. However, as a general rule, horizontal shading is considerably more effective at reducing solar admittance than vertical shading for Melbourne's climate and sun angles. Unless the design intent specifically calls for vertical fins, horizontal projection should be the primary lever. #### Step 4: Address the Wall U-Value Once the solar admittance target is resolved, attention turns to the wall glazing U-value. For facades that incorporate spandrel panels, this is where the performance can unravel quickly. Spandrel panels are, by their nature, thermally poor: they are typically single-skin aluminium or glass with minimal insulation, and a system R-value of around 1.0 is a realistic assessment of their performance.
To achieve compliance on the wall U-value target, the total system U-value generally needs to be reduced to approximately 2.6. This may require improvements to the spandrel assembly, the frame specification, or both. The calculator allows the proposed wall R-value to be adjusted independently of the glazing specification, making it straightforward to identify the minimum performance level required for compliance. #### Outcome Following the steps above, a compliant outcome is achievable for a Class 5 office in Melbourne at 50% window-to-wall ratio, with: * A triple low-e glazing system at approximately SHGC 0.26 * External horizontal shading of approximately 300mm projection * A total system U-value of approximately 2.6 This is not a particularly unusual specification. The glazing is procurable, the shading depth is architecturally manageable, and the wall performance target is achievable with standard construction details. The compliance pathway exists, it just requires deliberate design decisions rather than a default specification. *** ### Let's Wrap this Up Specification 37 represents a considered and reasonably pragmatic update to the facade energy efficiency provisions of the National Construction Code. It does not prohibit highly glazed facades, but it does require that those facades be designed with external shading and appropriate glazing specifications. This is not unreasonable: the principle that large areas of glass without shading generate cooling loads is not controversial, and the code is simply requiring that it be addressed explicitly. The [Facade Calculator](/user-guide/tools-and-plugins/ncc-2025-the-facade-calculator.md) provides a transparent and accessible means of evaluating compliance. It is free to use, it exposes the underlying equations, and it produces exportable results. For practitioners working to NCC 2025 in Victoria, it is the appropriate starting point for facade compliance assessment. The hierarchy of compliance decisions is clear: 1. Select the correct building class and climate zone. 2. Establish the window-to-wall ratio that the design intent requires. 3. Reduce the SHGC to the lowest value that is commercially procurable. 4. Apply external horizontal shading to meet the solar admittance target. 5. Verify and optimise the wall assembly to meet the U-value target. Following this sequence will, in most cases, produce a compliant outcome without requiring fundamental changes to the architectural intent of the facade. The code wants shading. Design for shading, and the rest tends to follow. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.betterbuilding.io/sign-up-and-plans/news-and-updates/2026/ncc-2025-facade-calculator-a-practical-guide-to-compliance.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.