Façade Calculator

As a performance-based code, the NCC provides various ways that a building design can meet minimum energy efficiency standards.

A 'Deemed to Satisfy' approach is one option.

This video outlines the use of the Façade Calculator to test a building design, using “Deemed to Satisfy” standards, and the provisions contained in J1.5 of NCC Volume One.

Changes to the NCC glazing performance requirements have broadened your ability to prove overall compliance for a building's façade.

This allows the use of more uniform glazing types on all aspects of a façade, using the Deemed-to-Satisfy Provisions.

While this provides greater design flexibility, correct calculations require you to enter a more detailed level of information to verify compliance.

The Façade Calculator applies to Classes 3 to 9 buildings, as well as the common areas of Class 2 buildings.

It can also accommodate mixed-use buildings.

The calculator is available from the ABCB website. This video will guide you through the process.

Use of this calculator is not mandatory. You can use any method to support your calculations, as long as they meet the requirements for Evidence of Suitability, described in

Clause A5.2 of the NCC.

The calculator should be used in conjunction with the NCC, which contains the defined meaning of a number of terms used by the tool.

One significant change in NCC 2019 is that you must now calculate the thermal resistance of the façade as a whole, rather than having separate requirements for walls and windows – although opaque wall elements still need to meet ‘backstop’ minimum total R-Value requirements.

Another change is that it is now possible to ‘trade’ performance between north, south, east and west aspects using a Deemed to Satisfy compliance pathway.

Even if one aspect does not meet the minimum requirements, the façade can comply as a whole.

The Façade Calculator – which is an Excel-based tool – helps you with all these calculations.

Use the navigation ribbon at the top of the page - or the tabs at the bottom - to move around the calculator.

Drop-down fields are grey – as opposed to the white fields which require data to be input.

The ABCB wants this calculator to be a useful and effective tool. As we become aware of any issues, we will list them on the ‘Known Issues’ tab until they are rectified. 

So please check here, or in the ‘Help’ guide, if you have any difficulties.

Context-sensitive tips will appear from time to time to help you complete the calculator. These pop-ups can be dragged to the side if required.

We’ll now step through the calculator, showing, by way of example, its use in the design of a theoretical student accommodation building in Melbourne.

There are 7 steps.

Step 1… Enter general information about the building.

The calculator should open on the ‘General Information’ page. If not, it is accessible from the first coloured square on the ribbon.

On this page, enter details about yourself…

… and the building…

… including classification… climate… and storeys above ground.

Information on climate zones and related resources are available by clicking on the map on this screen, or by visiting the ABCB website.

Step 2… Enter the glazing system information.

Click on the Glazing System information square on the ribbon.

Enter data, creating a unique reference for each glazing system…

… and select System…

… Glass…

… and Frame types from the pull-down menus.

When you select a glass type the calculator will automatically fill in the Glass U-value and Solar Heat Gain Coefficient from a built-in User Library.

Finally enter the Total System U and SHGC Values.

These values will vary depending on the window size and framing features, including sub-framing.

This information may be available from the window supplier, from the WERS database, or you may calculate it yourself.

One important aspect of the calculator is the inclusion of a customisable User Library.

While some generic values are pre-entered, the calculator is designed to be expanded upon over time. You can build your own library of values as you use the calculator. 

These values may be for individual façade elements, or entire wall systems.

Some data will be known to you, and some will need to be sourced from suppliers.

All user-defined items in the library will automatically be added to the relevant drop-down menu in the calculator.

Step 3… Enter the wall information.

This is done on the next tab – Wall Systems.

Here, you’ll enter the opaque wall information, to calculate its thermal resistance and the impact of thermal bridging.

There are two calculation methods available here.

The first is to enter information from the User Library. In this example, we’ll use a pre-set wall profile, with a known Total System R-value of point nine metres squared Kelvin per watt. (.9 m2K.W)

To this we add the wall thickness and solar absorptance.

If you don’t already know the Total System R-Value of the wall, the second method allows you to calculate it instead, by ‘building’ up information from the external layer, plus up to an additional 6 layers.

Again, individual materials and certain data can be accessed from the User Library, with additional information to be entered – such as layer thickness, framing thickness, width and area, and details of the Thermal Break.

In this example, we’ll use a solid concrete external layer, with a 20mm airspace, glass wool insulation, and cladding in gypsum plasterboard.

Select the level of ventilation in layer two. This will affect the thermal resistance of the air gap and all layers to the exterior.

Once the ventilation level is selected, the tool will calculate its effect, and combine layers two and three, with the total value of the two layers shown in layer 3.

Layer 2 shows as zero.

Based on all this information, the calculator will work out System R- and U-Values.

Once completed, this non-generic wall can now be added as a user-defined system in the User Library…

… for future use in the Wall Systems section on this tab.

Step 4… Enter the shading information.

There is also a tab for entering Shading Systems, where you enter the shading type – whether horizontal or provided by some other type of device –and dimensions.

There is no shading information to enter in this worked example.

Step 5 … Assess if the design meets minimum Deemed to Satisfy Requirements.

Next, move to the Wall Glazing Area plus Results tab.

This page is in three sections. The first…

… and third of these panels can be switched on and off to save screen space.

In the second panel, enter the areas of both the glazed and opaque elements of the façade.

Automatically using the unique references you entered on earlier sheets, the calculator will show Total Façade U and Façade Solar Admittance values, Glazing values and

Average Wall R-Values.

These results will appear as units in the Wall Glazing Area panel, with compliant results appearing in green fields, and non-compliant results in red fields.

Please remember, when entering data on this page, you can only use a given glazing, shading or wall reference once on each aspect. If you enter the same reference more than once, the calculator will not produce correct results for the façade.

If the wall and/or glazing is internal, check the “internal wall” box. This will mean that only the U-Value requirements are tested for that construction.

Overall compliance based on Method 1 – U-Value and Solar Admittance – and Method 2 – U-Value and AC Energy Value – is shown graphically in the Results panel.

In this example the envelope does not comply with the U-Value or solar admittance requirements via either method 1 or method 2. The opaque wall components, also don’t meet the backstop minimum Total R-Value requirements set out in Table J1.5a of the Code, so the proposed design does not meet minimum Deemed to Satisfy requirements.

The third panel on this tab shows the values for a reference building that would be required by JV3, based on data you’ve entered elsewhere.

If overall compliance has been achieved, go straight to Step 7.

If not…

Step 6… Make changes to the design or materials selected so that the building achieves compliance.

You can use the calculator to test the impact of various design changes.

These might include…

… reducing thermal bridging…

… upgrading insulation…

… reviewing the window and shading design…

… or other design amendments.

(pause)

When the calculator input reflects the final design settings…

Step 7… Report the results.

The calculator can generate a report summarising the results.

You’ll need to accept a Legal Disclaimer to enter this tab. Remember, all information needs to be checked and verified against the design documentation for compliance assessment.

Further details about the Façade Calculator – including additional examples – are provided in the Energy Efficiency Volume One Handbook, and other resources from the ABCB website.