An as-built verification (ABV) assessment gives confidence to builders and buyers that a home’s shell will perform to the standard that it has been designed to.
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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.
Why insulation coverage and air tightness are important
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.
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:
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.
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.
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.
Insulation integrity inspection
Thermal imaging and visual inspections are used to ensure that the insulation coverage consists of:
Before checking the walls, windows, doors and ceilings, the verifier/assessor heats or cools the home to create a temperature differential of between 5 and 10 degrees Celsius. This allows the thermal imaging cameras to identify missing or poorly installed insulation as well as draughts and airgaps.
The area of non-conformance is then calculated by comparing the area that was inspected to the area non-conformance. This is then registered and documented in the final ABV report.
Blower door test
Our methodology uses method one of 3 as detailed in Australian standard AS/NZS ISO 9972:2015 “Thermal performance of buildings – Determination of air permeability of buildings – fan pressurization method”.
In preparation for the test, the natural ventilation openings (windows and doors) are closed and the building’s mechanical ventilation or air conditioning openings are sealed (ducted heating and cooling vents, exhaust fans etc.).
Using a fan, the tester then blows air through the opening it is fitted to (usually the main entrance of the home), to create a differential pressure of 50 Pa when compared to the outside. The pressure can be negative or positive. SV recommends testing to both negative and positive pressures.
During the test, the verifier/assessor will look for leaks using a combination of smoke and thermal imaging. Air pressure is digitally logged and provides the required data to calculate the air permeability.
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.
For information on qualified testers/verifiers/assessors visit the Air Tightness Testing and Measurement Association or Air Infiltration and Ventilation Association of Australia.