Ventilation and airtightness: the key to a warmer home

We all like a bit of fresh air, and natural ventilation is nice, but when a home has lots of tiny gaps and cracks that reduce airtightness, the heating system can end up warming the outdoors as much as the indoors. Warm air slips out under skirting boards, around floor edges and window frames. Cold, damp air is pulled back in to replace it. Over time, that constant, uncontrolled airflow and air movement can increase heat loss and may contribute to condensation problems, especially where it creates colder internal surfaces or combines with poor ventilation.

When those unwanted escape routes are properly sealed, your radiators won’t have to work as hard. This means the warmth you’re paying for stays where you need it most. Airtightness primarily focuses on eliminating all unintended gaps and cracks in the external building envelope.

In a properly airtight and mechanically ventilated property, rooms feel more consistently comfortable with few air leakage pathways. They’re less affected by wind, and the usual cold spots that you might find around external walls and windows will start to disappear. This, in turn, helps to reduce problems such as mould growth, peeling paint and musty smells. Airtight buildings are also easier to maintain energy efficiency and meet heating needs to achieve desired indoor temperature conditions.

Why airtightness matters

For most of us, the aim of having a well-ventilated and airtight home is to reduce bills, improve comfort and cut carbon emissions. It’s a good way to achieve significant performance gains without changing how your home looks from the street. This can be particularly useful in conservation or heritage areas where the appearance of roofs, windows and façades can be carefully controlled.

Experts suggest that homeowners think about draught‑proofing and ventilation together. It is important to combine air‑sealing work with effective extract fans, and reduce unintentional leakage points. This is especially useful in older properties with a history of condensation or damp, but also applies to new buildings. And it needs to be managed carefully. Simple measures such as upgrading bathroom and kitchen extract fans, checking background ventilation and ensuring clothes are dried in well‑ventilated areas can complement more complicated airtightness work.

Improving airtightness and ventilation reduces heat loss and helps insulation work properly. Improving airtightness, along with other fixes, makes a big difference. Loft insulation, underfloor heating, and window upgrades will also help create a more comfortable and future-proof home, and a more energy efficient construction.

Whether you’re upgrading the airtightness on a heritage or more modern property, it’s important to understand the nuances of your home first. Then it’s important to combine measures such as thermal insulation, controlled ventilation and airtightness improvements so they work together. The Letchworth Retrofit House is a library of whole-house retrofit measures, considerations when undertaking action, and the specific implications of the design principles. It also helps you see which measures are best tackled when. This allows you to align works such as re‑plastering or new kitchens with airtightness and ventilation improvements, rather than undertaking them in isolation.

What is a good air-tightness test result?

An air tightness test is usually undertaken with a “blower door” test. This uses a fan in an external doorway to pressurise or depressurise the house and measure uncontrolled air leakage. In the UK, we express home measurements as air permeability in m³/(h⋅m²) at a pressure difference of 50 Pa (Pa stands for Pascals). Put simply, the lower the number, the less air leaks through gaps and cracks. Official UK government guidance sets the legal requirements for air permeability in England and Wales.​

The current regulations require a maximum air permeability of 8 m³/(h·m²) at 50 Pa for new dwellings (this changed from 10 in 2021). Many new homes now aim for around 5 m³/(h⋅m²) at 50 Pa, which is considered an achievable “average” target. A good energy-efficiency result is often between 3 and 5 m³/(h⋅m²) at 50 Pa. This is low enough to cut heat loss but not so low that you have problems without planned ventilation. The 1920s house we studied achieved a result of 6m³/(h⋅m²) at 50 Pa. This shows that just because your home is old doesn't mean it is any worse than a modern property.

A good aim is to achieve a sensible improvement and pair it with good ventilation. Working with a suitably qualified tester or retrofit professional can help you understand what is practical for your property.

What are airtightness membranes?

If you are building an extension, ask your builder about airtightness membranes. An airtightness membrane is a continuous layer, usually a flexible sheet material. It’s designed to stop unintended air leakage while still allowing the property to manage its moisture properly. Installers usually put these membranes on the warm side of the insulation (facing into the room) as part of walls, roofs or floors. Once complete, the membrane layer acts like a continuous skin around the inside of the building.

Modern airtightness membranes are typically used to create a continuous air barrier. This works where existing building materials are not inherently airtight, for example, in timber‑frame walls or roof build‑ups. They also complement internal wall or roof insulation so warm air cannot get through gaps and joints. Membranes also help control moisture in a building by acting as a vapour control layer. These are often designed so moisture can dry out in the right direction.

Airtightness tapes and detailing

Even a really good airtightness membrane will not work properly unless all the joints and edges are carefully sealed. Special airtightness tape is highly adhesive, durable, and compatible with most construction materials, creating a flexible, airtight seal. The tape will seal around pipes, cables, and ductwork, which can be common leakage points in retrofitted homes. Airtightness tape is also designed to cope with movement, temperature changes and the long life of a building. It’s also used for connecting membranes to things like masonry or window frames, where cracks can sometimes enable warm indoor air to leak out, and outside air to leak in.

Combining tapes and compatible sealants with other measures like careful wet plastering, floor sealing and improved window and door seals can significantly cut draughts. You should plan these room‑by‑room so that any airtightness work dovetails with other improvements such as new kitchens, bathrooms or redecoration. This reduces disruption and ensures that newly installed fittings are not opened up again.

Understanding your own home

Before undertaking an airtightness and ventilation refit, it is necessary to fully understand the condition of your home and how it breathes. It’s a good idea to start with a home energy survey to find obvious draughts and cold spots around floors, loft hatches, skirting boards and older extensions. You can even carry out your own informal checks using a smoke pencil (a handheld device that releases smoke to detect draughts) to find serious leaks.

Next steps

• Fix any damp or maintenance problems first – for example, leaky gutters, blocked drains or damaged pointing – because a damp wall is a cold wall and making your property more airtight might make problems worse.
• Before tackling draughts, consider how you will properly ventilate your home. Trickle vents in windows are not normally sufficient.
• Plan larger works, such as internal wall insulation with a continuous airtightness membrane and taping strategy, as part of a broader retrofit plan for your home.