What Happens When a Residential Design Changes During a VURB Assessment?

Residential Design Coordination

Residential designs continue to evolve after energy modelling begins. The important question is whether a change affects the assumptions or performance demonstrated by the assessment.

During a Verification Using a Reference Building (VURB) assessment, changes to architectural drawings, glazing specifications, insulation, shading or other building characteristics may affect the thermal comparison. Understanding when a revision needs review helps project teams maintain consistency between the model, compliance evidence and final construction documentation.

In Brief

Design Changes May Require the VURB Model to Be Reviewed

A VURB assessment evaluates a defined residential design against a compliant reference building using prescribed modelling conditions.

When the design changes, the project team should determine whether the revised information affects the building geometry, thermal characteristics, reference building assumptions or compliance conclusions.

Not every change requires a complete new simulation. Some changes may have no relevant effect, while others may require updated inputs, further calculations or revised compliance documentation.

The assessment should ultimately reflect the design and specifications being relied upon for approval and construction.

Model Integrity

Why Do Design Revisions Matter in a VURB Assessment?

A VURB assessment is based on a particular version of the proposed dwelling. Architectural geometry, glazing, construction materials, insulation and other relevant information are used to calculate the building's thermal loads.

The proposed building is then compared with a reference building established according to the applicable Verification Method.

If a relevant specification changes after modelling, the earlier result may no longer describe the current proposal accurately. This does not necessarily mean the dwelling would fail the comparison, but it means the effect of the change should be established rather than assumed.

The purpose of revision control is to maintain a clear relationship between the assessed design, the technical evidence and the drawings or specifications used for the project.

Comparative Modelling

When Does the Reference Building Also Need to Change?

Under national NCC 2022 H6V2, the proposed dwelling and reference building share prescribed characteristics, including the floor plan, orientation and location and size of glazing.

If a design revision changes one of these common characteristics, the reference building may also need to be updated so that the comparison continues to use the required consistent inputs.

For example, enlarging a glazed opening is not simply a change to the proposed building's window specification. The revised glazing dimensions must be reflected in the relevant common model geometry.

By contrast, changing the thermal performance specification of a window without altering its dimensions may primarily affect the proposed building model. The precise modelling response depends on the requirements of H6V2 and the information changed.

The reference building should not be retained unchanged merely for convenience if a revision affects a characteristic that must be common to both models.

These are illustrative review considerations, not fixed regulatory revision categories. The actual response depends on the nature of the change, the applicable requirements and the supporting assessment evidence.

Extent of Reassessment

Does Every Design Change Require a Complete New VURB Assessment?

Not necessarily. The need for further modelling depends on whether the revision affects the technical basis or conclusions of the existing assessment.

A change unrelated to the modelled building characteristics may be resolved through a documented review. A change to glazing, insulation, building geometry or other relevant inputs may require the model to be updated and the affected calculations repeated.

Where a change substantially alters the design, the scope of reassessment may be more extensive. A revised compliance conclusion should be based on sufficient evidence rather than an assumption that the original outcome will remain unchanged.

The NCC does not establish a universal numerical threshold for what constitutes a minor VURB design revision. The technical significance of each change must be considered in context.

Documentation Consistency

Why Must the Assessment Match the Current Drawings and Specifications?

A technically valid calculation is only useful when the building it represents can be clearly identified.

For a residential Performance Solution, the supporting documentation should identify the design and relevant assumptions assessed, the method used and the basis for the compliance conclusion.

Where architectural drawings and specifications are revised, the assessment documentation may need to be updated so that the model and design records remain consistent.

This is particularly important where product substitutions or drawing revisions occur after an earlier modelling result has been issued.

The required documentation and approval response depend on the project stage, the applicable regulatory framework and the relevant authority's requirements.

Project Coordination

A Practical Approach to Managing VURB Design Revisions

A structured review process helps project teams understand the technical significance of a revision before relying on an existing assessment result.

This is a practical coordination approach, not a separately prescribed five-step VURB procedure.

Timing and Project Delivery

When Should a Design Revision Be Sent for Review?

Potentially relevant changes should be raised before the revised design or specification is relied upon for compliance, approval or construction.

Early review is particularly valuable when changes affect glazing orders, insulation selections, external shading or building geometry, as these decisions can become difficult to reverse once procurement or construction progresses.

Where the project has already received approval, the team should also determine whether the change requires an approval amendment, additional evidence or another regulatory step. This is a separate consideration from the technical modelling update itself.

Keeping the assessment aligned with the latest coordinated documentation helps avoid uncertainty about which design version has been evaluated.

Residential Compliance Coordination

Has Your Residential Design Changed Since Its Energy Assessment?

Share your current drawings, previous assessment information and a summary of the proposed revisions. Certified Energy can review the applicable compliance pathway and advise what further technical assessment may be appropriate.