The ins and outs of as-built verification

Last updated: 15 December 2021

Even though homes are designed to meet specific energy-efficiency standards, errors during the construction process often prevent homes from delivering on the required standards.

With that in mind, how can you guarantee that a home has been built to meet the design criteria? Or give confidence to a home buyer that a home won’t be draughty, uncomfortable or unnecessarily expensive to heat and cool?

The answer is simple – undertake an as-built verification (ABV) assessment of the insulation coverage and air tightness. Before starting on your ABV journey, catch up on correct insulation installation including common errors and things to avoid.

Research and current requirements

Research conducted by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) showed that the average performance of Melbourne homes (assumed to achieve 6-star NatHERS) was 19.7 air changes per hour (ACH) at 50 Pascals (Pa). This is well outside compliance with the National Construction Code (NCC) (2019) which requires 10 ACH at 50 Pa.

When it came to insulation installation, of the homes assessed across Australia 67% were deemed to be of average or below average insulation coverage Despite this, there are currently no mandates in NCC (2019) to conduct an ABV of the insulation coverage and air tightness of a class 1a building.

Insulation requirements

Although routine on-site inspections may include review of insulation, trades persons completing other work (e.g. electrical work) after these inspections may move the insulation and not put it back correctly. Furthermore, there are only a small number of accredited insulation installers. With more than 60,000 homes delivered in Victoria each year, this means the industry is substantially unregulated.

Leaving gaps in the insulation:

  • reduces the energy efficiency of the thermal envelope
  • impacts on a home’s heating and cooling cost
  • increases risk of condensation resulting in mould and mildew.

Air tightness requirements

There is no requirement for builders in the residential market to check the air tightness of homes as part of routine inspections. This leads to situations where homes are marketed as high-end but are very uncomfortable (draughty) to live in and difficult to heat and cool.

Our ABV method

Sustainability Victoria (SV) worked in collaboration with an independent as-built verification company to develop, implement and test an ABV methodology. The methodology was developed to ensure that the homes delivered under SV programs were built to meet the criteria they were designed to fulfil.

The methodology was first tested successfully as part of the Zero Net Carbon Homes program and will be further used in the 7 Star Homes program. Although these programs set energy-efficiency parameters beyond minimum standards, the clear benefit of completing the test is the assurance that energy-efficiency requirements (whether at or above standard) haven’t been reduced during the construction phase.

house graphic with image callouts illustrating how insulation is checked An overview of SV’s as-built verification showing insulation integrity and blower door tests.

The assessment

The assessment process relies on existing standards and test methods including thermography and blower door testing as set out in AS/NZS ISO 9972:2015 ‘Thermal performance of buildings – Determination of air permeability of buildings – Fan pressurization method’.

The ABV assessment is made up of 2 components:

1. Insulation integrity inspection.

2. Blower door test.

Preparing for ABV assessment

While mistakes are sometimes unavoidable, the purpose of the ABV should be to verify the quality of the build as opposed to identifying errors made along the way.

The following will help you prepare for an ABV.

Before commencing construction

  • ensure the type of insulation and building wrap is appropriate for the home’s climate zone
  • check through the home’s plans and identify areas that pose a high risk or are difficult to insulate.
  • download SV’s ABV checklist and have it ready to reference during construction.

During construction

  • Follow the advice in SV’s ABV checklist.
  • Organise or conduct a visual inspection of building wraps, window installation and insulation at lockup stage, to pick up any issues before plaster goes up.

Post construction

  • Schedule your ABV assessment for when the home is ready for handover and all heating and cooling systems are installed and functional.

For information on qualified testers/verifiers/assessors visit the Air Tightness Testing and Measurement Association or Air Infiltration and Ventilation Association of Australia.