Air Tightness

Air tightness refers to how effectively a building prevents uncontrolled air from leaking in or out through gaps in its structure. A well-sealed home keeps heated air inside during winter and hot air outside during summer, while a draughty home loses energy constantly through invisible gaps.

Where air leaks happen

Air finds its way through surprisingly small gaps. Common leakage points include:

• Around windows and doors — gaps between the frame and the wall, worn seals, and poorly fitting doors
• At junctions — where walls meet floors, ceilings, or roofs
• Through the loft hatch — often poorly sealed and uninsulated
• Around pipes and cables — where services penetrate walls, floors, or ceilings
• Through floorboards — especially suspended timber floors with gaps between boards
• At electrical sockets and switches — on external walls, these can allow air to pass through the wall cavity
• Through chimneys and fireplaces — an open chimney acts like a ventilation shaft, pulling warm air out of the house

Why air tightness matters

Poor air tightness undermines your insulation investment. Imagine wrapping yourself in a warm blanket but leaving it open at the back — the blanket does its job, but cold air still reaches you through the gap. The same principle applies to your home.

Improving air tightness:

• Reduces energy bills — less heat escaping means less energy needed to maintain a comfortable temperature
• Improves comfort — eliminates cold draughts and uneven temperatures between rooms
• Helps prevent condensation — uncontrolled air movement can carry moisture into cold areas of the building envelope, causing condensation and mould
• Improves acoustic performance — if air can get through, so can sound

Air tightness vs. ventilation

An important distinction: air tightness is about stopping uncontrolled air leakage. You still need controlled ventilation — fresh air coming in where and when you want it, through windows, trickle vents, or mechanical ventilation systems.

The principle is: build tight, ventilate right. Seal the gaps to stop random draughts, then provide proper ventilation to ensure fresh air and moisture control.

Improving air tightness during renovation

A renovation is the ideal time to improve air tightness because walls, floors, and ceilings are often opened up. Practical steps include:

• Sealing around window and door frames with appropriate tapes or sealants
• Fitting draught strips to doors and windows
• Sealing gaps where pipes and cables penetrate walls and floors
• Insulating and draught-proofing the loft hatch
• Using airtight membranes behind dry lining or insulation
• Fitting chimney draught excluders or capping unused chimneys

These measures are inexpensive relative to their impact and are easiest to carry out while other work is in progress. Discuss air tightness with your general contractor when planning insulation or window upgrades.