Airtightness, Air Quality and Mould

A common misconception in Australia surrounds the root cause of mould within building envelopes.  In reality, both extremely leaky and overly tight buildings contribute to mould growth.  The chances of a building being too leaky are unfortunately quite high.  In this article we will show you how air tightness improves air quality and mitigates mould problems.

Buildings in southern parts of Australia can have huge temperature swings of 10˚C – 25˚C.

The above diagram explains the concept that warm air overall, can store more water inside it than cold air.  So, with large temperature swings, relative humidity also swings.

Research and monitoring performance.

The above graph shows humidity highs and lows with a home that was insulated and made more airtight (5ACH@50Pa) in mid-2015.  It changed the internal humidity performance of the building considerably. A swing of between 50 – 80% humidity changed to a swing of 45-62% after air tightness.

In the past, research was conducted using blower door testing of Australian buildings to understand the leakiness of our building stock.  It has been proven that they can be extremely leaky, and yet there are many companies out there who’s the whole purpose is to clean up mould that occurs in buildings. This does not address the cause of this mould in the first place. Controlling humidity is really important to reduce the chances of condensation/mould occurring, and a side effect of tackling this problem improves comfort.

Indoor air quality and health

Humidity can contribute to mould and dust mite colonisation when it’s consistently above 60%, this can trigger asthma or other health conditions.

Some of the mould species that contribute to asthma and other health conditions mostly thrive in 70% humidity, which can occur in most homes when temperature swings occur often, especially in wet areas like bathrooms.

Low levels of humidity greatly effect comfort but can also contribute to the spread of viruses like the flu or the common cold, as well as eczema aggravation.  In Australia, higher humidity levels are more common, especially on the east cost of the country.

Here is an excellent resource which goes into more detail of the health consequences of high and low humidity levels.

http://www.sensitivechoice.com/indoor-humidity/

 

Controlling humidity by knowing what’s going on in your environment:

The most important step that can be taken is reducing temperature swings and humidity level spikes to lower the chances of cold surfaces developing the home. This in turn mitigates the amount of condensation that can form.

There are devices available today, that can monitor humidity, CO2, air quality, and temperature, sending an alarm to a smartphone when events occur. Armed with this knowledge, windows can be opened when needed or heating/cooling appliances can be used, to keep internal temperature/humidity in check.

Insulate surfaces

Un-insulated or conductive surfaces like aluminium window frame surfaces will still be at high risk of condensation, and mould issues. The more that can be done to insulate conductive surfaces from transferring cold temperatures from outside to inside, the less chance condensation may occur. Insulation consistency is of paramount importance especially in bathrooms where humidity can get extremely high, and condensation can easily occur.

The warmer the surfaces are inside the building envelope, and the fewer air leaks, the more constant the temperature, and the more constant relative humidity. This is beneficial in warm and cold climates.

Heating and Cooling with split systems

Refrigerated air conditioners can reduce absolute humidity when they are in cooling mode.  Reverse cycle units, when in heating mode, reduce relative humidity because heated air can store more moisture.  It’s basically being moved further away from dew point (condensation point).

Air tightness and controlled ventilation

In order to benefit from air tightness, it is important to understand that eventually a building too airtight may then need to introduce energy recovery ventilation (ERV) or Heat recovery ventilation (HRV), depending on the type of climate a building is located in.  An air quality monitoring device can be used as a building gets more and more airtight, alarming occupants of CO2 greater than 1000 parts per million (ppm). A high-performance building envelope means that CO2 levels can be controlled by opening a door, or a window, during the day when outdoor air temperatures and humidity levels are ideal. ERV/HRV systems take care of controlling CO2 ppm, while also filtering dust and pollen and recovering energy from the stale air.

By blower door testing a building, it can be quickly understood whether a building is airtight enough to move towards mechanical ventilation with energy recovery. In an ideal world, no uncontrolled air exchange should be leaving a building.

 

State of mind

In order to maintain and control indoor air quality, there are 3 states of mind one should be in.

State of mind 1

No air tightness works done on the home

Monitor indoor air quality with an AWAIR environment monitor that alerts you of high CO2, humidity/temperature level extremes.

Actions: Prompt you to open windows or put on heating or cooling devices to manage air quality.

Result: Learn about and understand your indoor environment, potentially end up using more energy

State of mind 2

Air tightness works have been undertaken

Monitor indoor air quality with an AWAIR environment monitor, that alerts you of high CO2, humidity/temperature level extremes.

Actions: Air quality sensor can prompt to open windows or put on heating or cooling devices to manage air quality.

Results: Improved energy efficiency and air quality, vermin proofing the home and reducing dust inside.

State of mind 3

Air tightness works to the extreme

Blower door test the building and get the air tightness below 10 Air changes per hour at 50Pa of pressure.

Actions: Install heat recovery or energy recovery ventilation, which also has dust and pollen filters.

Results: Much better energy efficiency, vermin proofing the home, significantly reduced dust and particulate indoor, reduced pollen count in summer.

Retrofitting air tightness and insulation

There are many products and services available in the Australian marketplace to improve air tightness and insulation consistency:

• Wall air tightness and insulation can be retrofitted with Enviroflex insulation and caulk can be used on skirting boards, and around window architraves.
• Floor insulation can be sealed and insulated with spray foam or insulated with batts and sealed with a new coat of varnish.
• Ceiling fans can be draught proofed with draught stoppers or replaced with fans that include draught stoppers.
• Ducted heating system outlets and returns can be sealed with caulk behind the removable grill. A return outlet in an internal wall cavity can improve air tightness and energy efficiency, due to high pressures in ducted heat systems.
• Wall ventilation installed pre-1980’s used in conjunction with gas heating systems or open fireplaces can be closed up.  Seek professional advice before doing this, especially if you still use an old wall mounted gas heating system or fireplace.

Finally…

If you are serious about energy efficiency and indoor air quality for health, do the following:

1. It’s a great idea to monitor the air quality within a building using an air quality monitoring device.  If it is not known a problem exists, steps can’t be taken to fix it.
2. Organise a contractor to conduct a blower door test, once you have made the building as airtight as possible.  It’s important to know where the building is at. Customers can Contact us for more information.
3. Get a home to below 10ACH@50Pa and then consider heat recovery ventilation.  That way, you don’t need to open up windows to keep CO2 levels low.

Having indoor air quality is all about reducing uncontrolled ventilation and implementing controlled ventilation combined with insulation consistency.