Does your home still feel draughty, even when the heating is on full blast? Are you planning a renovation to lower your energy bills, but unsure how airtightness fits in alongside insulation?
Are you worried that increasing airtightness in your home might increase the risk of condensation and damp?
If so, in this blog, we explain what airtightness is and why it’s one of the lesser known areas to create a healthy, sustainable home.
Airtightness is important for a low energy home
When planning a renovation or a new build, there may be a conversation you have with your architect or builder around insulation.
While insulation is undoubtedly critical for retaining heat, it is only part of the equation when keeping your home warm. Another vital component is airtightness.
Think of your home as a bucket with holes, and the air in your home as the water that can leak through these hole. Insulation is like sponges inside the bucket that slow the water getting out but doesn’t stop it completely.
If you increase the airtightness it seals up the holes and prevents the water or comfortable air in your home escaping and cold air getting in.
What is airtightness?
Airtightness is the measure of how much air leaks in and out of a building through unintentional gaps. In standard construction, a home is rarely a sealed envelope.
There’s tiny cracks and holes everywhere, particularly where the floor meets the wall, around windows and doors, and wherever pipes or cables penetrate the external walls.
Current building regulations in England still allow for a surprising amount of air leakage. It has been likened to having a hole the size of a 20 pence piece in every single square metre of your building envelope.
If you added all those small holes together, you would end up with a gaping window open to the winter air all year round. That is hardly keeping warm air in and cold air out.
When a home is not airtight, you face a constant cycle of energy loss where your heating system works hard to warm the air, only for it to escape immediately through these thousands of tiny gaps.
Measuring performance with Air Changes Per Hour
The leakiness of a home is often measured with a metric called Air Changes Per Hour (ACH). This figure represents the number of times the entire volume of air inside your house is replaced by outside air within a sixty minute period. The lower the number, the more airtight and energy efficient the building is.
To put this into perspective, a typical older property that has not been renovated might have an around 13 air changes per hour.
This means that every single hour, you are effectively paying to heat the entire volume of air in your house thirteen times over.
In contrast, a high performance home is often designed to achieve a rating of less than one air change per hour.
While building regulations generally require new builds to achieve around 5 air changes per hour, pushing for a lower number than this standard will result in significantly warmer home that’s cheaper to heat.
How does an airtight home breathe?
A common concern is that sealing a house too tightly will make it stuffy or cause damp issues because the house can’t breathe. However, it’s important to distinguish between uncontrolled air leakage and the breathability of materials.
Air leakage is simply draughts carrying heat out and bringing cold, damp air into the building.
Breathability, on the other hand, can refer to the use of vapour permeable materials that allow moisture to escape naturally without letting the heat out. Or materials that can absorb moisture from the air when it’s humid and release that moisture when the air dries out.
The aim is to create a home that is airtight to prevent draughts but uses breathable materials to manage moisture and prevent condensation.
The role of ventilation in air tight home
In an airtight home, ventilation changes from being accidental to being controlled.
With a leaky home, you don’t want to rely on dusty cracks to provide you and your family with fresh air. Once you sealed these uncontrolled air leaks, you should introduce a designed system to breathe for the building.
A proper ventilation strategy ensures that stale, humidity-laden air is consistently removed from source areas, while fresh air is supplied to living spaces.
This provides a healthier indoor environment and eliminates the risk of condensation, giving you fresh air exactly where and when you need it.
How airtightness can protect your home
Having a more airtight home is also important to maintaining the building’s physical health.
In a house that isn’t properly sealed, warm, moisture-laden air internally from activities like cooking or showering is forced through tiny cracks and gaps in the construction.
As this humid air travels through your walls or roof and hits colder surfaces, it turns back into liquid water, known as interstitial condensation.
Because this dampness is trapped deep inside the structure, it often goes unnoticed but can create mould or damage the structure of your home.
By creating a solid airtight barrier, you block these hidden pathways, keeping your home dry, sturdy, and free from the mould that can impact your indoor air quality.
Building for the future
Ultimately, airtightness is the difference between a house that looks efficient on paper and one that actually feels warm to live in.
While it requires attention to detail and a shift in how we think about construction, the benefits are considerable.
By sealing the small gaps in your building fabric and pairing this with a considered ventilation strategy, you prevent constantly reheating cold air and you get a home that’s draught-free, healthy and cheaper to run.
Do you have a leaky bucket of a home?
Don’t let your heating leak out of your home and speak with the experts who know how to create a warm, healthy home.