The most common sources of air leaks

Air leaks reduce the thermal performance of a building and the main culprits are openings and cracks in the building’s walls and roof.​

Air leaks can lead to excess moisture, which leads to mould and other health risks. It also has a host of other downsides and living in a building with air leaks is considered both dangerous and expensive. 

Understanding Air Flow 

Exfiltration is a term used to explain the occurrence of air exiting a building through an uncontrolled manner such as cracks; whilst Infiltration is the opposite and occurs when air enters a building.  

Ventilation refers to fresh air that moves in and out of a building by way of design. Ventilation decreases stuffiness and unpleasant odours, and also helps control the amount of moisture in a building. 

Generally, a builder’s main aim is to construct a building with controlled ventilation, striving to reduce air leaks as much as possible.  

We already know that energy-efficient buildings are a growing trend in Australia therefore, constructing an airtight building is a good way to keep up with the times. 

In fact, it is a prerequisite in many Australian states to design an insulated building in order to obtain a number of certifications including a BASIX and NatHERS Certificate.  A Thermal Performance Assessment is conducted prior to finalising the DA (development application) to determine the most efficient building materials, window options and other necessary specifications. 

Moisture control and mould 

Air leaks may also lead to moisture accumulating on walls often causing mould deposits to form which can have an immediate effect on those residing in the building. 

How Mould Can Affect Your Health  

Inhaling mould fragments or spores can inflame the airways, causing nasal congestion, wheezing, chest tightness, coughing and throat irritation. Prolonged exposure to high levels of indoor dampness can reduce lung function and cause chronic health problems such as asthma.  

Mycotoxins can kill neurones in the brain, which directly affects our mental capacity and can alter our psychological makeup. Some of the neurological symptoms of the ingestion of mycotoxins include confusion, dizziness, a ‘foggy’ brain, hallucinations, seizures and trembling. 

Other important symptoms to look out for, relating to respiratory, circulatory and other conditions, are difficulty breathing; bleeding gums; nose bleeds; cold and flu symptoms; vomiting blood; wounds that won’t heal; blurred vision; nausea; and jaundice. Infection from damp and mould is very serious so it is imperative that if you notice any of the above symptoms you seek medical attention.  

There is also evidence that mycotoxins are carcinogenic, which can lead to the growth of cancers. 

Overall, airtight buildings are not only in the best interest of one’s health, they and more comfortable to live in and have a higher Thermal Performance Rating making them far more energy-efficient than those with uncontrolled air leaks. 

The most common causes of air leaks 

There are many different ways for uncontrolled air to enter a building therefore; the first step is to identify the cause of each air leak.  

Construction details 

Depending on the structure of the building, there may be leak-prone areas that require special care. Below are some construction choices that lead to a higher likelihood of draughts. 

Lack of drywall 

Buildings that have dropped ceilings and angled staircase ceilings are considered less airtight. This is because these areas often lack an additional layer of plaster or drywall. The same is true for knee walls – short, upper-level walls that fit to the slope of a roof as shown in the below image.  

In some buildings, the areas behind skirting boards may lack proper insulation too. 

Generally, these are problems builders will deal with however; homeowners also have some effective solutions at their disposal.   

Unfaced fibreglass insulation

An effective way to stop airflow from an attic spreading through the entire building is to hire an experienced tradesman who can wrap unfaced fibreglass insulation in plastic, sealing the air leak (as shown below).

Basements and in-house garages 

When a building or home has a basement, it is naturally more prone to air leaks and in most cases, the cold air comes directly from the foundation. Many older houses may require extensive modifications in the basement area, but caulking the gaps is an excellent stopgap measure. Garage doors can also be subject to weather-stripping as well.  

Recessed lights 

This form of lighting is a common source of air leakage. Each light needs to be insulated separately which can be costly and time-consuming. In the case of new homes, the owners might be advised to opt for a different way to position lights. 


Wind is another factor that can seriously impact the amount of air leakage. On the windward face of the building, wind creates a higher pressure zone which leads to infiltration on that side. The non-windward walls are subject to lower pressure instead, which is where most of the exfiltration occurs. 

In both cases, the best option is to seal the gaps and cracks on the surface of the walls. Let’s look at some examples of how to do that. 

Doors and windows 

Residents will experience draughts and drops in temperature around doors and windows where the most significant leaks occur. Homeowners can combat these air leaks by weather-stripping every door.  

Note: Weather-stripping also works with insufficiently sealed windows however; in the case of windows that don’t open, caulking can be an appropriate solution as well. 

Unfortunately, for old buildings, the doors and windows often need a full reconstruction. In this case, although it may be a lot of extra work, the solution is to install new doors and windows 

In the case of new buildings, it’s important to select high-quality windows and doors that seal well, otherwise you may regret it later. 

Pipes and kitchen units 

Air leaks are common around sink pipes and soil pipes. Additionally, they can happen through, the panel beside the tub, behind kitchen counters and behind appliances.

In short, leaks can be a problem anywhere where there is pipe penetration. 

Sometimes, these gaps are an error in construction, but they can also be created later, in the case of plumbing repairs. 

This problem has a fairly straightforward solution. If the gaps are smaller than 1/4 inches across, it’s enough to caulk them. For homeowners, it’s usually best to use acrylic latex caulk. This is easy to apply even if you have little experience with household repairs. 

In the case of larger gaps (up to 3 inches), soft foam is necessary. This is another affordable and easy-to-use tool. 

Electric cables and fittings 

Much like plumbers, electricians can leave gaps through the drywall. This is another problem that people can solve by caulking and it doesn’t usually require expert help. The first step is to find all the draughts around electric fittings and other installations. 

Stack effect 

The way warm air moves through the building creates a stack effect. As the lighter warm air flows up a building and through the roof, it is replaced by the heavier cold air. This puts pressure on the upper levels of the building and the attic. 

Once again, dropped ceilings tend to cause problems and need proper insulation. Properly sealed windows are a must-have.  

As energy-efficient buildings become the norm, it’s now even more important to make buildings airtight. 

Air leaks can cause a great deal of damage to a building’s integrity, and they are costly as well. Finding ways to fix this problem should be a priority for homeowners and builders alike. Some repairs are simple but others require major changes. 

Installing new doors and windows is one of the most effective ways to combat air leaks. For instance, louvre windows can help make your building more energy-efficient. They are a good choice for builders looking to improve the building’s star rating and create a pleasant, safe interior space.