Alternative Solution or Verification Using a Reference Building (VURB)

If you want to minimize construction costs related to energy efficiency, i.e. glazing and slab insulation costs, the best approach to take for NCC energy compliance is called Verification Using a Reference Building (VURB) method. This method is flexible and allows insulation reduction in some parts of the building by adding more insulation to others.

VURB method is also the last resort for energy compliance when all other avenues cannot provide compliance.

Energy Compliance service guarantee:

If we can’t reduce your construction costs by more than twice the value of our service fee, and you decide not to use our report, then you won’t have to pay the remainder of our invoice.

This might appear to be too good to be true but; here is how it works:

10 steps for demonstrating energy compliance using VURB

  1. Model the geometry of the house as per final architectural plans
  2. Apply heating and cooling setpoints as specified in NCC and time of use of the rooms/spaces
  3. Apply schedules for people’s occupation and equipment operation (that generate heat inside the house)
  4. Use NCC Glazing Calculator to calculate minimum NCC DtS requirements for the glazing and assign them to the building
  5. Apply minimum DtS insulation requirements (NCC 2019 Vol 2.0 Table V2.6.2.2) to the roof, walls and floor. Save the model and call the building as “Proposed building based on DtS requirements”.

FACT: NCC 2019 assumes an efficient standard Australian house should have ceiling not higher than 2.4m. Also, Roof should be pitched at 23 degrees.

  1. Apply the above facts to step 5 and call it “Reference Building”. Run the model and calculate annual heating and cooling demand.
  2. Minimize the building cost for the “Proposed Building”. We may do this with low-cost thermal improvements such as adding insulation to the model from Step 5. Other low-cost means are shading size optimization or addition of shading devices to offset summer heat gains through glazing. If glazing cost is not the biggest concern, modify the cost minimization strategy. Addition of insulation to other parts of the building can reduce high-cost added insulation to the slab or existing walls.
  3. Run the Proposed Building with low-cost improvements. Proposed buildings are deemed compliant if its heating and/or cooling demand is less than the Reference Building in step 9.
  4. Iterate & optimize improvement to the Proposed Building in step 8 until you get to the sweet spot that offers the highest cost-saving. We have had cases with over 30 iterations.
  5. Complete the report.


Do I need an energy assessment or energy rating?

Whenever you are building a new residential dwelling or undertaking a major extension or alteration to your existing house, you’ll have to obtain a building permit from your governing council. In the process, you may come upon some difficulties regarding energy efficiency compliance for your development. Difficulties emerge from the high cost of building insulation and/or glazing to comply with the code. This includes, for instance, installing double or triple glazed windows or adding insulation to an existing slab.

So how do you overcome this problem? Or in a better sense, how could you get your building permit while reasonably reducing your construction costs?

At Energy Compliance, we offer all avenues to satisfy energy efficiency requirements for your house while considering how to decrease construction costs. Up to now, the most promising method to do so is called Verification Using a Reference Building or VURB in short.

Can you use VURB for commercial buildings?

Yes, and No! VURB is a term NCC uses for an alternative solution for residential buildings (Class 1a buildings to be more accurate). For commercial buildings, NCC refers to an alternative solution called JV3 modelling which is similar to VURB with fewer restrictions and easier compliance.

Click here for more information on NCC building classes.

FACT: For residential buildings, NCC doesn’t allow the use of onsite solar electricity to offset electricity demand and CO2 reduction. However, for commercial buildings, NCC allows the use of onsite solar electricity generation or any other renewable solution to offset CO2 emissions associated with the building energy demand. For a commercial building, it also allows electricity and gas reduction through the use of better than MEPS certified equipment to assist with energy compliance.

What are all options to an NCC energy compliance for a residential building?

There are three ways to demonstrate energy compliance for your residential building:

  • Elemental provisions: there exists a set of prescriptive provisions for insulation of building fabric, glazing thermal performance, building sealing and air movement. The only drawback of this approach is that it is very rigid; therefore, you cannot change any of the required provisions. This approach is generally called DtS elemental provisions.
  • Star rating: this method is another DtS method of demonstrating compliance for energy efficiency under NCC. This method considers a building is deemed to comply with NCC energy efficiency provisions, provided the building obtains at least 6 stars from one of the NatHERS accredited tools.

CONs of above DtS approaches: The outputs of the above DtS approaches are proved to increase the cost of construction. This is certainly true for buildings with large floor areas or large ratio of glazing to floor areas.

  • Verification Using a Reference Building (VURB): this method allows for a more realistic energy modelling of a building. Energy assessor undertakes VURB through an energy modelling software capable of analyzing the energy demand of the house in an hourly manner. Due to this hourly analysis and the various realistic inputs from the actual house, the results of this method (if done professionally) are deemed to address a meaningful energy demand of the house. In this approach, different elements of the house (e.g. windows and roof) are integrated in a way that the whole building is assessed holistically.

PROs of VURB method: Unlike NatHERS Star Rating method which compares a two-dimensional model of the building to a set of figures prebuilt into software, VURB method compares the building with itself and allows maximizing the accuracy and cost-saving.

How to do VURB?

Unlike Star Rating scheme that allows for an evaluation of buildings using so-called “stars”, VURB is a pass or fail approach. If you pass the energy efficiency test using VURB method, what it would mean is that your building complies with the NCC energy efficiency provisions. There are 4 steps for a building to passed the test using VURB method:

  1. Model the Proposed Building:
    • Obtain architectural plans. Model the building geometry according to the supplied architectural plans using an accredited 3D building modelling software.
    • Add building fabrics insulation, glazing thermal properties, solar absorptance values and shadings according to it.
    • Run the computer model of the Proposed Building on an hourly basis, using the closest weather station data, and calculate heating and cooling demand.
  2. Model the Reference Building:
    • Edit the Proposed Building geometry as per NCC Reference Building requirements.
    • Add building fabric type, insulation and solar absorptance values as per NCC Reference building requirements. Glazing thermal performance and shading must be according to NCC Glazing Calculator.
    • Run the Reference Building on an hourly basis, using the same weather data, and calculate heating and cooling demand.
  3. Evaluate the results:
    • Depending on the Climate zone, heating and/or cooling demand of the Proposed Building must be equal or less than that of the Reference Building. If this is the case, then the Proposed Building gets a pass.
    • If this is not the case, then you must run the Proposed Building again, using more insulation, changed solar absorptance values, optimised shadings, optimised window SHGC, better glazing U-values and introduction of shading devices.
    • This process continues until you get a pass, meaning that the Proposed Building is more energy-efficient than the Reference Building.
  4. Prepare the report


What are the pros of VURB?

Every method for energy compliance has its pros and cons, hence there is no single perfect solution for all types of houses and it depends on several aspects. For the ease of referencing, we put aside Elemental Provisions and only compare Star Rating to VURB. Here are some pros of VURB method with respect to the Star Rating method:

  • Reduction in construction costs (especially glazing):
    Energy modelling tools account for heat stored or released from the ground:
    The soil beneath the slab works like a thermal battery that stores and discharges heat from the house. Therefore, it has a great capacity to offset the heating or cooling demand of the house. Thermal mass is more accurately considered in VURB method. Hence, buildings with a slab on ground have a higher chance to have a cheaper construction cost with VURB.
    Holistic integration of building zones and their fabrics and glazing:
    Energy modelling tools allow for a more complex integration of building elements in energy balance, and hence the model may represent a deeper sense to obtain building energy demand. For example, solar heat gains from a large window can be transmitted inside the room and absorbed by the concrete slab with a high thermal mass. In the sun’s absence, the heat is then transformed back into the zone and offsets heating demand. Therefore, large north glazing, to a degree may be beneficial to some houses if the complex nature of the building fabric integration could be understood and undertaken. In our experience, buildings with large glazing to floor area ratio may gain better deals using VURB than the Star Rating method. 
  • Best practice for the prediction of building heating and cooling demand in the design stage:
    Determine the size of HVAC equipment and annual energy use:
    Outcomes of energy modelling from VURB closely represents the actual energy demand of the Proposed Building. This information is useful to architects, builders and especially the building services engineers. Once the HVAC equipment size is determined, it’s easier to locate their location with respect to the view, weight, and to estimate the overall cost of the HVAC system.
    Undertake feasibility analysis for different energy source options:
    Hour by hour heating and cooling demand of the proposed building is the key parameter to estimate what equipment or renewable option is most feasible for the building. It’s wise to consider referring to a professional feasibility assessment company that also undertakes VURB option for energy compliance. Once the Proposed Building is modelled and deemed to be compliant, the hour by hour results can also be used to determine what energy source option is the most suitable to meet the building demand.
  • Unlike NatHERS, Class 1b can also benefit from Performance Solutions using VURB option:
    NatHERS Star Rating involves Class 1a, but VURB covers both Class 1a and Class 1b building.

Click here for further information on NCC building classification.

What are the cons of VURB?

Here are some cons of VURB method with respect to the Star Rating method:

  • VURB doesn’t cover Class 2 and Class 4 part of a building:
    Only NatHERS star rating covers Class 2 and Class 4 buildings as there are no Elemental Provisions for Class 2 and Class 4 buildings.
  • VURB is relatively more expensive to undertake:
    3D modelling takes more effort than 2D modelling:
    NatHERS accredited tools model the building in a two-dimensional form and also generate reports that are valid for submitting, but this is not the case under VURB. Accurate 3D modelling of a complex building takes much more effort and therefore relatively more expensive to undertake. However, construction cost reduction is usually more than the energy assessor fee. To mitigate this risk to our clients, at Energy Compliance, we offer:

Service guarantee: If we can’t reduce your construction costs by more than the twice the value of our service fee, and you decide not to use our report, then you won’t have to pay the remainder of our invoice.

What are NCC Reference Building requirements?

NCC Reference building is a building that has the same geometry of the clients proposed building but for the sake of energy efficiency modelling, NCC requires you to modify it as per below:


Reference Building roof

Proposed building can have a roof of any shape and material. However, NCC requires you to compare it to a standard roof that most average Australian houses have. Therefore, NCC reference building should have a roof at 23 degrees with solar heat absorptance value of 0.6.

Reference Building ceiling

Proposed building can have a ceiling with any height or a sloped cathedral ceiling for that matter. However, NCC requires you to compare it to a minimum ceiling height of 2.4m for a habitable room. This ceiling must also be flat to the exclusion of any cathedral ceiling.

Reference Building ground floor

Proposed building can have a suspended floor above ground floor level. However, NCC requires you to compare it to a building having a concrete slab on ground. Ground temperature fluctuation is lower than the ambient weather and relatively closer to the temperatures where people feel comfortable. This temperature stability together with a higher concrete thermal mass, is the reason why NCC requires comparison between Proposed Building and Reference Building having a concrete slab on ground.

Reference Building roof lights

Proposed building can have any number of roof lights. However, NCC requires you to compare it to a building having no roof lights. NCC Vol 2.0 Part 3.8.4 allows roof lights for habitable rooms with no or minimum means of daylighting. As roof lights add to the building cooling demand, NCC requires Proposed Buildings to have minimum to no roof lights.

Examples of improvements through VURB

Following are dozens of projects where Energy compliance managed to reduce construction costs. Click on each project to read more.