Residential Thermal Performance Modelling
A reference building comparison is only meaningful when the proposed dwelling and its benchmark are assessed under consistent conditions.
Verification Using a Reference Building, or VURB, compares the calculated heating and cooling loads of a proposed residential building with those of a compliant reference building. Under NCC 2022 H6V2, the required comparison depends on the climate zone, the modelling method and the prescribed assumptions used for both buildings.
In Brief
VURB Compares Thermal Loads Against a Compliant Reference Building
Under NCC 2022 H6V2, the proposed dwelling and reference building are modelled using the same calculation method and prescribed common assumptions.
The reference building must satisfy the relevant Deemed-to-Satisfy requirements for building fabric, external glazing and ceiling fans. The proposed building is modelled using its intended specifications, subject to the requirements of the Verification Method.
The resulting heating and cooling loads are compared according to the applicable climate-zone criteria. In climate zones 2 to 7, both the heating load and cooling load must be no greater than their corresponding reference building values.
A favourable modelling comparison is an important part of verification, but it does not remove other requirements that must still be satisfied.
Understanding Thermal Loads
What Do Heating and Cooling Loads Represent?
A heating load represents the calculated thermal energy needed to maintain the modelled indoor heating conditions over the assessment period. A cooling load represents the corresponding energy needed to maintain the modelled cooling conditions.
These loads are influenced by heat transfer through the building envelope, solar gains through glazing, air movement, internal heat gains and the local climate.
A dwelling may have relatively low heating demand but substantial cooling demand, or the reverse. The relationship depends on climate, building orientation, construction and other modelled characteristics.
Heating and cooling loads are not the same as measured household electricity consumption. They describe modelled thermal demand under defined conditions rather than the actual energy bills of future occupants.
Comparative Modelling Structure
How Are the Proposed and Reference Buildings Modelled?
H6V2 requires the proposed building and reference building to be assessed using the same calculation method and a defined set of common inputs. This establishes a controlled comparison rather than two unrelated simulations.
The common inputs include location-specific climate and topographical data, orientation, floor plan, glazing location and size, number of storeys, relevant adjoining features and specified building operation assumptions.
The reference building applies construction and performance assumptions consistent with the relevant Deemed-to-Satisfy provisions. The proposed building represents the intended design and specifications, subject to the requirements and limitations of H6V2.
The purpose is to isolate the thermal performance differences permitted by the method, rather than allowing changes in occupancy, weather, building layout or other prescribed common assumptions to distort the comparison.
Model Comparison
Proposed Building vs Reference Building: What Changes?
| Modelling consideration | Proposed building | Reference building |
|---|---|---|
| Calculation method | The selected compliant modelling method | The same modelling method |
| Climate and location | Location-specific climate and topographical data | The same prescribed data |
| Orientation and floor plan | Actual project orientation and layout | The same orientation and layout |
| Glazing location and size | Actual window positions and dimensions | The same positions and dimensions |
| Building fabric | Intended construction specifications, subject to retained direct requirements | Relevant DTS-compliant building fabric assumptions |
| Glazing performance | Proposed glazing performance specifications | Relevant DTS-compliant glazing assumptions |
| Occupancy and operation | Prescribed occupancy, internal gains and operating schedules | The same prescribed assumptions |
| Assessment output | Calculated heating and cooling loads | Corresponding benchmark loads |
This table summarises the comparison. H6V2 prescribes additional common inputs and modelling conditions that must be followed in a formal assessment.
Climate-Specific Verification
How Do Climate Zones Change the Heating and Cooling Criteria?
The national H6V2 method under NCC 2022 does not apply one combined heating and cooling threshold across every climate zone. It establishes different comparison requirements according to the NCC climate zone in which the proposed building is located.
| NCC climate zone | Required comparison under H6V2 |
|---|---|
| Climate zone 1 | Proposed cooling load must be equal to or less than the reference building cooling load. |
| Climate zones 2, 3, 4, 5, 6 and 7 | Both proposed heating load and proposed cooling load must be equal to or less than their corresponding reference building loads. |
| Climate zone 8 | Proposed heating load must be equal to or less than the reference building heating load. |
For climate zones 2 to 7, a reduction in heating load does not automatically compensate for a cooling load that exceeds its reference value. Each required comparison must be satisfied.
These are the national NCC 2022 H6V2 criteria. Jurisdictional variations, including the Northern Territory's separate provisions, must be checked independently.
Calculation Method
What Modelling Method Does H6V2 Require?
H6V2 requires the comparison to use a calculation method other than house energy rating software.
The calculation method must comply with ANSI/ASHRAE Standard 140 and be capable of modelling the required thermal influences, including building fabric, glazing, shading, air infiltration, ventilation, internal heat gains and relevant surrounding conditions.
The climatic data must be based on hourly recorded values representative of a typical year for the proposed location. H6V2 also specifies common operating assumptions, including heating and cooling schedules, thermostat settings and internal gains.
Using sophisticated simulation software does not, by itself, establish compliance. The method, input assumptions, reference building construction and resulting comparisons must satisfy the applicable Verification Method.
Interpreting Model Results
What Does a Successful VURB Comparison Demonstrate?
A successful comparison demonstrates that the proposed building satisfies the applicable heating and cooling load criteria relative to its compliant reference building, using the required calculation method and assumptions.
The result is relative to the reference building rather than a universal numerical heating or cooling target. Different dwelling configurations, locations and climate conditions can produce different reference loads.
For climate zones 2 to 7, the results must demonstrate that both relevant loads meet their respective reference values. A favourable total or combined result is not a substitute for satisfying the individual comparisons required by H6V2.
The modelling results form part of the technical evidence supporting the relevant Performance Solution. They should be accompanied by sufficient documentation of the method, assumptions, specifications and applicable compliance requirements.
Assessment Limitations
What Does the VURB Model Not Establish?
A VURB comparison is not a prediction of the exact energy consumption, running costs or indoor temperatures that occupants will experience after construction.
Actual performance depends on construction quality, installation, weather, occupant behaviour, ventilation practices, heating and cooling systems and other factors that may differ from the prescribed modelling assumptions.
H6V2 also does not independently verify all residential energy efficiency requirements. Separate provisions, including those relating to energy usage under H6P2 where applicable, must be addressed through the appropriate compliance pathway.
A technically favourable simulation should therefore be understood as evidence for a defined NCC requirement, not as a complete building performance certification.
Compliance Beyond the Comparison
Can a Favourable Load Comparison Replace Every DTS Requirement?
No. H6V2 retains direct compliance requirements for specified aspects of the proposed building.
These include identified provisions for building fabric thermal insulation, thermal breaks, floor edge insulation and building sealing. For sealing, H6V2 identifies the relevant Housing Provisions or the H6V3 verification approach.
The reference building comparison cannot be used to disregard these retained obligations simply because the proposed building achieves a favourable heating or cooling result.
A complete assessment must address both the applicable modelling criteria and the additional provisions required by the selected compliance pathway.
Model Input Quality
Why Does Accurate Project Information Matter?
The reliability of a VURB assessment depends on the accuracy and consistency of the information used to represent the proposed dwelling.
Architectural drawings, glazing schedules, construction specifications and relevant site information help establish the building geometry and proposed thermal characteristics.
Incomplete or conflicting information may require assumptions that need to be clarified before a formal compliance conclusion can be reached. Where specifications change, the model may also need to be reviewed to determine whether the previous results remain representative.
For the detailed documentation requirements, see VURB Assessment Documents: A Residential Submission Checklist.
Frequently Asked Questions
VURB Heating and Cooling Modelling Questions
Does VURB combine heating and cooling into one compliance score?
No. Under national NCC 2022 H6V2, climate zones 2 to 7 require both heating and cooling loads to be no greater than the corresponding reference building loads. Climate zone 1 requires the cooling comparison, while climate zone 8 requires the heating comparison.
Can better heating performance compensate for excessive cooling demand?
Not where both loads must independently satisfy the reference building comparison. In climate zones 2 to 7, a proposed dwelling must meet the required heating and cooling criteria separately.
Does VURB use NatHERS software?
The national H6V2 method requires a calculation method other than house energy rating software. It is a comparative verification method, not a NatHERS star rating assessment.
Must both models use the same weather and occupancy assumptions?
Yes. H6V2 specifies common climate, occupancy, operating and other modelling assumptions so that the comparison is made on a consistent basis.
Does a passing VURB model prove the home will have low energy bills?
No. The model assesses thermal loads under prescribed conditions. Actual energy bills depend on equipment, occupancy, operation, tariffs, weather and other factors beyond the verification comparison.
What happens if the proposed heating or cooling load exceeds the reference value?
The relevant H6V2 comparison criterion has not been met. The project team may need to review modelling inputs, investigate permitted design or specification changes, or consider another appropriate compliance approach. A successful outcome cannot be assumed.
Can VURB modelling be used for a residential project in NSW?
H6V2 does not apply under the NSW variation to NCC 2022 Volume Two. The appropriate NSW compliance requirements and assessment pathway must be established separately.
Related Guidance
Continue Exploring VURB and Residential Energy Compliance
Knowledge Hub
VURB Assessment and Reference Building Compliance
Explore the broader verification method, compliance framework and project suitability.
Jurisdictional Requirements
Where Can VURB Be Used in Australia?
Understand NCC editions, state variations and the NSW H6V2 exclusion.
Pathway Comparison
VURB vs Residential DTS
Compare reference building verification with direct elemental compliance.
Project Preparation
VURB Assessment Documents
Review the drawings and technical information needed to support assessment.
Residential Performance Assessment
Understand the Thermal Performance Requirements for Your Project
Share your project location, current drawings and proposed construction specifications. Certified Energy can review the applicable compliance requirements and advise whether a reference building assessment or another residential energy efficiency pathway is appropriate.
Explore VURB Assessment ServicesLast reviewed: October 2026. This article explains the national H6V2 provisions under NCC 2022 Volume Two. Applicable NCC editions, jurisdictional variations and project-specific approval requirements must be confirmed. Part of the Certified Energy Residential Compliance Knowledge Hub.
