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ACH or Air Permeability?

Air Changes per Hour (ACH) and Air Permeability are both measures used in the context of building physics, particularly when discussing air tightness and leakage.

However, they represent different aspects:

  • ACH is a measure of the air volume or flow through a Blower Door added to or removed from a space/enclosure/room divided by the volume of the space, air changes per hour is a measure of how many times the air within a defined space is replaced. If you are spending money to heat or cool this air and it is leaking out, it is a good idea to have a strategy to reduce the ACH number.

  • Permeability is a measure of the ability of a material to allow the passage air through it. Air Permeability leakage rates are often used in the context of building physics to understand the rate at which air can leak through the building envelope or the flow through a Blower Door divided by the area (floor + walls + ceilings) of the enclosure.

Australian Building Codes prefer to use Permeability as a measure of Building sealing.

BCA Vol 1 – J1V4 & BCA Vol 2 – H6V3 use 10 m3/hr.m2 at 50 Pa of pressure difference as a method of assessing the level air tightness in a building.

If you building is lower than 5 m3/hr.m2 you will be required to provide mechanical ventilation to provide fresh air and remove carbon dioxide and water vapour from the building.

This ventilation forms part of the condensation management strategy to reduce the risk of mould growth inside a building.

If you would like further information about this, please email or call!

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What is Air tightness?

Air tightness refers to the measure of how well a building prevents the uncontrolled flow of air through its envelope, which includes the floors, walls, roof, windows & doors.

It’s about eliminating all unintended gaps and cracks to create a healthy, comfortable, and energy-efficient living environment.

This is crucial because air leakage through these unintended openings can account for up to 50% of heat loss in a building.

To achieve high levels of air tightness, buildings must be designed and constructed with attention to sealing potential leaks, and then tested to ensure that the air leakage has been minimized.

Proper ventilation systems are also essential to maintain air quality.

In summary, air tightness is a key component in the construction of energy-efficient buildings, ensuring that insulation performs effectively and that the internal environment is both comfortable and cost-effective to maintain.

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Passive House – Smoke Test

60 second video on identifying leaks with smoke.

An interesting test when IR won’t work as good due to the temperature.

Smoke works well at pre cladding stage!

If we can help you please let us know.

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What is a Blower Door Test?

A blower door test is a diagnostic procedure used to measure the airtightness of buildings.

It can identify air leakage and help improve energy efficiency.

During the test, a blower door fan is mounted into an external doorway, and either pressurises or depressurises the building to reveal unsealed cracks and openings through which air can enter or escape (infiltrate or exfiltrate).

This process is crucial for determining how much air leaks in or out a home, which can impact heating and cooling costs, comfort levels, and indoor air quality.

Professionals use this test to recommend improvements and ensure that heating and cooling systems are properly sized. The results of a blower door test can guide homeowners in making targeted upgrades to enhance their home’s energy performance and comfort.

Here’s how it works:

  • The blower door fan depressurizes the house by pulling air out, which lowers the indoor air pressure.
  • The higher outdoor air pressure then flows in through all unsealed cracks and openings.
  • A pressure gauge, called a manometer, measures the pressure differences inside and outside the home.
  • The rate at which air infiltrates the home is recorded, often in terms of Air Changes per Hour (ACH).
  • The test can also be conducted in reverse, with the fan blowing air into the house to create positive pressure. During the test, professionals may use an infrared camera or a smoke pencil to detect the specific locations of air leaks.

Blower door tests are important for several reasons:

  • They help reduce energy consumption due to excess air leakage.
  • They prevent moisture condensation problems and uncomfortable drafts.
  • They control the entry of outdoor contaminants, pests, and odours.
  • They assist in determining the proper sizing of heating and cooling equipment.
  • They indicate whether mechanical ventilation is needed to maintain indoor air quality.

ATTMA | Registered Air Tightness Testers – Australia (bcta.group)

ABCB Building Code Building Sealing Verification

If you would like to arrange a Blower Door Test or have any questions, please contact us!