Thermal Comfort DIY method FAQs

The most common queries about the BASIX DIY method fall into three areas:

  1. Conditions of using the DIY method
  2. Tips to pass DIY
  3. Window selections to comply with BASIX commitments

1. Conditions of using the DIY method

QUESTION 1.1: Can I use the DIY method for my proposed dwelling?

The DIY method was developed as a simple way of assessing the performance of a house.

Underlying the DIY method are assumptions about house design, construction materials and methods. These assumptions were developed based on a sample of dwellings across a range of specifications and conditions. Under the DIY method, you will be asked questions as you enter the BASIX thermal comfort section to ensure the right assumptions are applied to your project.

Before using the DIY option for a single dwelling project, make sure that the proposed dwelling satisfies ALL the criteria listed on the screen. One of the criteria is that the conditioned floor area of the proposed dwelling must not be greater than 300m2. Some of the criteria will form part of the commitments on the BASIX certificate.

The full list of criteria underlying the use of the DIY method is available here.

The DIY method is not appropriate for all dwelling types. If the design of the proposed dwelling does not meet any of the criteria for the DIY option, you will need to use the Simulation method which allows greater flexibility in relation to the design.

QUESTION 1.2: My proposed dwelling consists of a garage at ground level and two storeys of living areas and bedrooms above the garage. Does it satisfy the conditions for using the  DIY method?

Since the ground-level garage is not a habitable area, your proposed dwelling is still regarded as having two storeys in the context of the DIY method. You are able to use the DIY method to achieve the BASIX thermal comfort requirements.

QUESTION 1.3: My proposed dwelling has an outdoor mezzanine or an alfresco area exceeding 25m2. Does it satisfy the conditions for using the DIY method?

Although you can’t use the DIY method for an indoor mezzanine (an intermediate floor open to the floor below) greater than 25m2,  you can use it for an outdoor mezzanine and/or alfresco area, which is specified in the same way as a balcony in BASIX DIY.

QUESTION 1.4: My project satisfies the criteria for using the DIY method, but it still fails the thermal comfort requirements no matter what I do. Why?

Simply because a dwelling satisfies the criteria for using the DIY method does not necessarily mean that it will achieve the BASIX thermal comfort requirements. The criteria for using DIY do not cover details about construction materials, glazing type and how the glazing is oriented and/or shaded. These details will affect the estimated heating and cooling loads and determine if the proposed dwelling satisfies the BASIX thermal comfort requirements.

You can follow the tips on this page to find out what you can do to pass DIY.

QUESTION 1.5: My project used to satisfy the BASIX requirement with the DIY method, but it fails the thermal comfort requirements after July 2017. Why?

Since 1 July 2017, the thermal comfort heating and cooling caps have become more stringent. Because of this change, existing house designs that used to be able to satisfy the BASIX thermal comfort requirements may not be able to do so.

You can follow the tips on this page to find out what you can do to pass DIY.

QUESTION 1.6: I have several house plans that score 6 to 7 NatHERS stars when using the Simulation method, but they fail the BASIX requirements when using the DIY method. Is there a glitch in the DIY method?

The DIY method requires far fewer inputs to specify a given house design than the Simulation method. In some cases, this reduced flexibility results in a higher level of stringency. The DIY method is therefore not a full substitution for the Simulation method. DIY also has limitations in terms of criteria underlying its use, and the insulation requirements as shown on BASIX commitments.

The DIY method is intended for use with typical house designs using common construction materials and methods. It specifies the minimum insulation requirements of the proposed dwelling. To better account for the benefits of higher insulation levels, especially on heating loads, and to account for specific design and construction features in bespoke architectural house designs, we recommend using the Simulation method.

QUESTION 1.7: Why can’t I specify an insulation level higher than the minimum requirements in DIY?

The DIY method was developed as a simple way of assessing the performance of a house. It is similar to the Deemed-to-satisfy (DTS) elemental method in the National Construction Code (NCC). The DTS elemental method prescribes the minimum insulation requirements of the building fabric and the maximum allowable performance from external glazing.

The minimum insulation requirements in DIY are lower than those prescribed in the DTS elemental method due to concerns of condensation and the feasibility of installing high levels of insulation inside the layers of the building envelope.

The DIY method provides an option to commit to a higher level (up to R1.0) of minimum insulation requirements. To better account for the effects of higher insulation levels on thermal performance, especially heating loads, we recommend using the Simulation method.

2. Tips to pass DIY

If your project is not able to pass DIY, refer to the following flowchart to find out what you can do:

Thermal Comfort DIY Method FAQs flowchart

QUESTION 2.1: I cannot get my project to pass DIY and found that both heating and cooling loads are too high. What should I do?

Step 1: Check if the total glazing area falls within the range suitable to the DIY method

The DIY method is suitable to your project if the total glazing area constitutes 10 – 40% of the conditioned floor area. Please refer to QUESTION 1.1 on the criteria for using the DIY method.

What should I do if the total glazing area falls outside the range suitable to the DIY method?

If the total glazing area falls outside the range suitable to the DIY method, you can go to the “Status” page and click on the “List of things you must address” link – see Figure 1.

Figure 1 – Status pageFigure 1 – Status page. Click image for larger view

A pop-up window will then appear indicating the total glazing area and how it compares with the conditioned floor area of your dwelling. A sample message is shown in Figure 2.

 Figure 2 – Sample message when total glazing area falls outside range suitable to DIY methodFigure 2 – Sample message when total glazing area falls outside range suitable to DIY method. Click image for larger view.

If the area of glazing is too high, you may want to consider the number and size of windows to reduce the heating and/or cooling load. For example, you can consider reducing the size of windows in the southerly orientation to reduce the heating load.

In addition, you can follow Step 2 to commit to a higher level of minimum insulation, and Step 3 to improve glazing specifications.

Step 2: Committing to a higher level of minimum insulation

To reduce the heating load, you may choose to commit to a higher level of minimum insulation requirements of:

  • external walls (other than cavity brick) by an additional R1.0,
  • suspended floors by an additional R0.5, or
  • ceiling and roof by an additional R1.0

To reduce the cooling load, you may choose to commit to a higher level of minimum insulation requirements of:

  • external walls (other than cavity brick) by an additional R1.0,
  • ceiling and roof by an additional R1.0

The optional questions to commit to a higher level of minimum insulation are shown in the sample screenshots of Figures 3 to 5. You can find the questions in the Construction Details section of the DIY method. The increase in the minimum insulation requirements will be reflected in the BASIX commitments.

Figure 3 – Sample screenshot showing the optional question to commit to an additional R1.0 for external walls.Figure 3 – Sample screenshot showing the optional question to commit to an additional R1.0 for external walls. Click image for larger view

Figure 4 – Sample screenshot showing the optional question to commit to an additional R0.5 for suspended floorsFigure 4 – Sample screenshot showing the optional question to commit to an additional R0.5 for suspended floors. Click image for larger view.

Figure 5 – Sample screenshot showing the optional question to commit to an additional R1.0 for ceiling and roofFigure 5 – Sample screenshot showing the optional question to commit to an additional R1.0 for ceiling and roof. Click image for larger view.

Step 3: Improving glazing orientation, shading and specifications

To reduce the heating load, you may want to consider the following:

  • Increasing the amount of sun entering the windows by moving them to the north, northeast or northwest – and in some cases to the east and/or the west;
  • Reducing the size of windows facing south, southeast and southwest;
  • Reducing the size of eaves or levels of fixed shading. In some cases, you can consider removing the fixed shading devices, or replacing them with adjustable shading to allow winter solar access;
  • Reducing the heat loss during winter by selecting glazing with lower U-value.

To reduce the cooling load, you may want to consider:

  • Reducing the area of windows facing west, east or northwest;
  • Increasing the size of eaves or levels of shading.
  • Selecting glazing with a lower solar heat gain coefficent (SGHC) value to reduce heat gain during summer;

Refer to the help note on the U-value and SHGC of the 88 default window selections available in the DIY tool.

With the exception of single clear or double clear glass, and aluminium or timber/uPVC/fibreglass frames, the frame and glass descriptions are for references only. BASIX compliance is checked by satisfying the acceptable range of U-value and SHGC value as shown on the certificate.

Note that some of the measures outlined above have opposing effects on heating and cooling loads. For example, selecting windows with lower SHGC values reduces the cooling load, but it also increases the heating load. An optimal combination of glazing selections needs to be made to balance the effects on both heating and cooling loads.

Step 4: Design changes or Simulation method

If your project is still not able to pass DIY after Steps 1 to 3, you may need to consider changes in design such as orientation of the proposed dwelling. The use of the Simulation method will facilitate design changes as it allows more flexibility in relation to the design.

QUESTION 2.2: I cannot get my project to pass DIY and found that the heating load is too high. What should I do?

If the cooling load of your project is significantly lower than the cap, you can consider reducing the heating load by:

  • Committing to a higher level of minimum insulation for external walls (except cavity brick), suspended floors and ceiling/roof;
  • Increasing the amount of sun entering the windows by moving them to the north, northeast or northwest - and in some cases to the east and/or the west;
  • Reducing the size of windows facing south, southeast and southwest;
  • Reducing the size of eaves or levels of fixed shading. In some cases, you can consider removing fixed shading devices or replacing them with adjustable shading to allow winter solar access.
  • Reducing the heat loss during winter by selecting glazing with a lower U-value.

Refer to the helpnote on the U-value and SHGC value of the 88 default window selections available in the DIY tool.

With the exception of single clear or double clear glass, and aluminium or timber/uPVC/fibreglass frames, the frame and glass descriptions are for references only. BASIX compliance is checked by satisfying the acceptable range of U-value and SHGC value as shown on the certificate.

If you are still unable to pass DIY, you may need to consider changes to the design of your house and/or its orientation. The use of Simulation method will facilitate design changes as it allows more flexibility in relation to the design.

QUESTION 2.3: I cannot get my project to pass DIY and found that cooling load is too high. What should I do?

If the heating load of your project is significantly lower than the cap, you can consider reducing the cooling load by:

  • Committing to a higher level of minimum insulation for external walls (except cavity brick), and ceiling/roof;
  • Selecting glazing with a lower SHGC value to reduce heat gain during summer;
  • Reducing the area of windows facing west, east or northwest;
  • Increasing the size of eaves or levels of shading.

Refer to the helpnote on the U-value and SHGC value of the 88 default window selections available in the DIY tool.

With the exception of single clear or double clear glass, and aluminium or timber/uPVC/fibreglass frames, the frame and glass descriptions are for references only. BASIX compliance is checked by satisfying the acceptable range of U-value and SHGC value as shown on the certificate.

If you are still unable to pass DIY, you may need to consider changes to the design of your house and/or its orientation. The use of the Simulation method will facilitate design changes as it allows more flexibility in relation to the design.

QUESTION 2.4: The heating load of my project is too high. I have tried to select higher-performance windows, but I cannot see any changes to the heating load outcomes. Is there a defect in the DIY tool?

The DIY method estimates the heating and cooling load outcomes based on the minimum required insulation levels and the windows and skylights you specified.

You may be able to avoid selecting high-performance windows by committing to a higher level of minimum insulation for external walls (except cavity brick), suspended floors and ceiling/roof.

Heating and cooling loads estimated from the DIY method are indicated as discrete segments in the infographic from the online interface. Slight improvements in the heating load may not trigger a move from one segment to the next, and thus not register as a change in the infographic.

3. Window selections to comply with BASIX commitment

QUESTION 3.1: I have selected aluminium double-glazed windows and did not find any U value and SGHC value on the BASIX certificate. However, U-value and SGHC values are shown for other window type selections. Why?

Part of a sample certificate is shown in Figure 3:

 Figure 3 – An extract of a sample BASIX certificate on the glazing sectionFigure 6 – An extract of a sample BASIX certificate on the glazing section. Click image for larger view.

For compliance, building certifiers do a visual inspection of glazing with single clear or double clear glass, and aluminium or timber/uPVC/fibreglass frames. No U-value and SHGC value are therefore included for these types of windows on the BASIX certificate – see the red boxes in Figure 3.

Note that the aluminium frames in this context refer to simple frames and NOT thermally broken aluminium frames.

QUESTION 3.2: I have selected a window that satisfies the U-value and SHGC value requirements on the BASIX certificate, but the descriptions of the window do not match those on the certificate. Does it matter?

For all window types other than single clear or double clear glass, and aluminium or timber/uPVC/fibreglass frames, compliance is checked by comparing the U-values and SHGC values of the installed windows with the range listed on the window table of the BASIX certificate. The frame and glass types shown on the certificate are for reference only. They are an indicative, but not exclusive, description of the type of window that is likely to satisfy the U and SHGC values. The certificate shows the range of U-values and SHGC values required for compliance, as highlighted in the blue boxes in Figure 3.

QUESTION 3.3: I initially selected a hinged window in DIY for the BASIX certificate, but later decided to switch to a sliding window. Do I need to revise the BASIX certificate to reflect this change?

If the window contains single clear or double clear glass, and aluminium or timber/uPVC/fibreglass frames, we recommend that you revise the certificate to ensure it shows the correct thermal comfort outcomes of the proposed dwelling.

For other window types, check with the window manufacturers if a sliding window satisfying the acceptable ranges of U-value and SHGC value for BASIX compliance is available. If not, you will need to revise the BASIX certificate and satisfy the heating and cooling load requirements.