The ins and outs of as-built verification
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.
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- Good thermal performance: insulation integrity and low air leakage make homes warmer in winter and cooler in summer.
- Indoor environments that are free of draughts: cold draughts can be felt through gaps in the building’s shell and make for uncomfortable living conditions. It can be difficult and costly to heat draughty homes.
- Low risk of condensation: areas that are missing insulation can cause surfaces to be cooler than their surroundings. These can become depositories for condensation which will cause mould and mildew. Mould and mildew pose a significant risk to the health of the home’s occupants.
- Lower energy bills: homes that have low levels of air-permeability are easier to heat and cool, as there is a lower rate of air-change with the outside. This means less reliance on heating and cooling systems resulting in less energy use and lower energy bills.
- Less wear and tear on mechanical systems: homes that have less need for heating and cooling cause less wear and tear on heating and cooling systems, extending their functional life, saving money for the homeowner and reducing embodied energy.
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.
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.
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Thermal imaging and visual inspections are used to ensure that the insulation coverage consists of:
- The correct thickness or R-value of insulation in the ceiling.
- Insulation integrity of 95% or above in each element i.e. 95% in the walls and 95% in the roof.
- Insulation that is in direct contact with the plaster and therefore performing correctly.
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.
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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.
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.
Videos
Watch these videos for specific ABV information: