Building Fabric

Draught Sealing and Air Leakage in Existing Homes

Draughts are one of the most noticeable comfort problems in existing homes.

A home can have insulation, new appliances and even solar panels, but still feel uncomfortable if uncontrolled air leaks allow cold air in during winter or hot air in during summer.

Draught sealing is the process of reducing uncontrolled air movement through gaps, cracks and openings in the building fabric. It can improve comfort and energy performance, but it needs to be balanced with healthy, controlled ventilation.

Why draughts matter in existing homes

Many existing Australian homes were built with less attention to airtightness than modern high-performance buildings. Over time, gaps can also appear around windows, doors, floors, roof spaces, service penetrations and renovation junctions.

When uncontrolled air moves through the home, heating and cooling systems may need to work harder. Rooms can feel uncomfortable even when the thermostat suggests the home should be warm or cool.

This is why draught sealing can be one of the most practical building fabric upgrades to consider before replacing systems or adding more technology.

What is air leakage?

Air leakage is uncontrolled air movement through unintended gaps in the building fabric. It is different from intentional ventilation, which is planned and controlled.

Common air leakage paths include:

• gaps around external doors
• gaps around windows
• open fireplaces and chimneys
• old wall vents
• exhaust fans without proper backdraft control
• floorboard gaps
• skirting board gaps
• ceiling penetrations
• downlights and service penetrations
• plumbing and electrical penetrations
• junctions between old and renovated areas

These leakage paths can be small individually, but together they can significantly affect comfort and energy performance.

Draught sealing is not the same as insulation

Draught sealing and insulation both affect comfort, but they solve different problems.

Insulation slows heat transfer through ceilings, roofs, walls and floors. Draught sealing reduces uncontrolled air movement through gaps and cracks. A home can be insulated but still draughty, or sealed but still poorly insulated.

For that reason, both should be considered as part of the whole building fabric. For more context, see Insulation in Existing Homes.

How draughts affect comfort

Draughts often create discomfort before they show up clearly in energy data. A room may feel cold around the ankles, uncomfortable near windows or doors, or difficult to heat evenly.

In summer, air leakage can allow hot outside air into the home, especially during heatwaves or windy conditions. In winter, cold air can enter while heated indoor air escapes, making the home feel colder than expected.

This can lead to higher heating and cooling use because occupants keep adjusting systems to compensate for the leaky building fabric.

How air leakage affects energy performance

Air leakage can increase heating and cooling demand because conditioned air is lost and outdoor air enters the home. This can make systems run longer or work harder to maintain comfort.

The effect depends on climate, wind exposure, building type, occupant behaviour and where the leakage occurs. In some homes, a few major leakage paths may have more impact than many small gaps.

A home energy rating or assessment can help identify whether air leakage is likely to be part of the performance problem.

Common draught sources in existing homes

Common draught sources include:

• external doors without seals
• sliding doors and old window frames
• gaps around skirting boards
• old floorboards or subfloor gaps
• open fireplaces and unused chimneys
• wall vents and legacy ventilation openings
• ceiling penetrations
• recessed downlights
• exhaust fans
• rangehoods
• plumbing and electrical penetrations
• junctions around extensions or additions

A useful review looks for patterns rather than assuming every gap has the same impact.

Doors and windows are common leakage points

Older doors and windows often leak air around seals, frames, tracks and joints. Sliding doors, timber windows, poorly fitted external doors and older aluminium frames can all contribute to draughts.

This is why glazing and draught sealing should often be reviewed together. A window may have poor thermal performance because of the glass, the frame, the seal or a combination of these issues.

For more context, see Glazing and Shading in Existing Homes.

Fireplaces, vents and exhaust openings can leak air

Open fireplaces, unused chimneys, old wall vents, exhaust fans and rangehoods can allow air movement between inside and outside. In some homes, these can be major leakage paths.

The correct response depends on whether the opening is still required for safety, appliance operation, combustion air or ventilation. Some openings can be sealed or improved. Others may need to remain functional or be replaced with controlled ventilation.

This is why draught sealing should be assessed carefully rather than handled as a blanket “seal everything” exercise.

Ceiling, floor and service penetrations can matter

Air leakage is not only around doors and windows. It can also occur through ceiling penetrations, gaps around downlights, exhaust fans, plumbing pipes, electrical conduits, floorboards and subfloor openings.

These leakage paths can connect living spaces to roof spaces, wall cavities, subfloors or outside air. In windy conditions, the effect can become more noticeable.

When sealing these areas, safety and compliance matter. Electrical, exhaust, combustion and ventilation requirements should not be compromised.

Renovation junctions can create air leakage

Existing homes often contain junctions between old and new construction. Extensions, converted garages, roof additions and reconfigured rooms can create gaps or inconsistent sealing where materials meet.

These junctions can be difficult to diagnose because the problem is sometimes hidden behind finishes or located at the boundary between building stages.

Renovation is often a valuable time to address air leakage because walls, ceilings, floors and services may already be accessible.

Airtightness needs controlled ventilation

A more airtight home is not the same as a poorly ventilated home. The goal is to reduce uncontrolled air leakage while still providing healthy, intentional ventilation.

This distinction is important because sealing gaps without considering ventilation can increase moisture, condensation and indoor air quality risks. Bathrooms, kitchens, laundries and bedrooms may all need appropriate ventilation strategies.

A good retrofit approach is not simply “make the home as sealed as possible.” It is to reduce unwanted leakage and manage fresh air deliberately.

How air leakage relates to a home energy rating

A home energy rating may consider air leakage, sealing quality or draught-related features depending on the assessment pathway. In some contexts, formal airtightness testing may provide more precise information. In others, assessor observations and available evidence may guide the review.

Air leakage is part of the wider building fabric picture. It interacts with insulation, glazing, shading, ventilation, heating and cooling systems.

For a broader explanation, see What Does a Home Energy Rating Actually Measure?

How an assessor may review draughts and air leakage

An assessor may look for visible or likely air leakage paths as part of the broader home energy rating process. The level of detail depends on the assessment pathway and whether formal testing is required or available.

Useful information may include:

• rooms that feel draughty
• doors or windows that rattle in wind
• visible light around door or window gaps
• known fireplace, chimney or vent issues
• areas where curtains move even when windows are closed
• renovation junctions that feel leaky
• ceiling or floor penetrations
• rooms with moisture, condensation or ventilation concerns

For more context, see What Does a Home Energy Rating Assessor Look For?

Renovation is often the best time to address air leakage

Draught sealing is often easier when renovation works are already exposing walls, ceilings, floors, windows, doors or services. Once finishes are complete, some leakage paths become harder to reach.

This is especially relevant for extensions, roof works, window replacement, floor repairs, kitchen and bathroom renovations, services upgrades and whole-home retrofits.

For renovation context, see Existing Home Energy Rating vs Renovation Energy Assessment.

What should not be sealed without advice?

Some openings may be required for ventilation, appliance safety, combustion air or moisture management. These should not be blocked without proper advice.

Be careful with:

• gas appliance ventilation
• combustion air openings
• bathroom, kitchen and laundry exhaust systems
• subfloor ventilation
• roof space ventilation
• moisture-affected areas
• heritage building elements
• areas with mould or condensation issues

The goal is controlled performance, not unsafe sealing.

What information helps a draught and air leakage review?

Before requesting a home energy rating or upgrade review, it can help to record where draughts are felt and when they occur.

Useful information may include:

• rooms that feel draughty
• photos of doors, windows and visible gaps
• notes on fireplaces, vents or exhaust fans
• areas that feel cold near floors or skirtings
• rooms with condensation or moisture concerns
• renovation history
• known window or door replacement history
• any existing energy or comfort reports

For a full preparation checklist, see What Information Do You Need for a Home Energy Rating?

FAQs

Why does draught sealing matter in existing homes?

Draught sealing matters because uncontrolled air leakage can make an existing home feel cold, hot, draughty or difficult to condition. Sealing gaps can improve comfort and reduce heating and cooling demand when done with appropriate ventilation.

What is air leakage in a home?

Air leakage is uncontrolled air movement through gaps, cracks and penetrations in the building fabric. It can occur around doors, windows, floors, ceilings, exhaust fans, downlights, chimneys, vents, service penetrations and poorly sealed construction joints.

Does a home energy rating assess draughts or air leakage?

A home energy rating may consider air leakage, sealing quality or draught-related features depending on the assessment pathway, available information and whether formal testing or assessor observations are used.

What are common sources of draughts in existing homes?

Common draught sources include gaps around doors and windows, open fireplaces, wall vents, exhaust fans, floorboard gaps, ceiling penetrations, downlights, plumbing penetrations, poorly sealed skirtings and gaps between old and renovated areas.

Is draught sealing the same as insulation?

No. Insulation slows heat transfer through building elements, while draught sealing reduces uncontrolled air movement through gaps and cracks. Both can affect comfort and energy performance, but they solve different problems.

Can a home be sealed too tightly?

Yes. Airtightness should be balanced with controlled ventilation. If a home is sealed without adequate ventilation, moisture, condensation, indoor air quality and mould risks may increase.

Home Energy Rating Review

Unsure whether draughts are affecting your home’s performance?

A home energy rating can help identify whether draught sealing, air leakage or other building fabric issues should be part of your upgrade pathway.

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