Carrying out an air tightness test can show you where energy is being lost in your home – and therefore how to reduce your bills.
In this guide you’ll learn:
- How air tightness affects your energy bills
- What score existing homes typically have, and what’s achievable
- Why ventilation matters just as much as sealing up
- How to know whether testing is worth it for your property
Air Tightness in Existing Homes: The Scale of the Problem
The vast majority of buildings that will exist in 2050 have already been built. The UK government has set a goal to reduce national greenhouse gas emissions by 80% below 1990 levels, and reaching that means a substantial amount of retrofit work on existing dwellings – including finding ways to improve their air tightness.
Improving air tightness is one of the most effective ways to reduce energy use in a dwelling, though it’s always best to improve other aspects alongside it, such as the quality of thermal insulation and the efficiency of the heating system.
Existing houses often have an air tightness score of around 15 (m3/h/m2@50pa). This is a poor score when compared to the standards set by regulation. Building Regulations (Part L1A) state that new builds must achieve a score of 10 or lower and most new builds need to reach 5 or lower to pass their SAP calculations and produce an EPC. Most existing houses could safely be brought down to a 5.
‘Build tight, ventilate right’
If your house doesn’t already have one, you’ll need to install an adequate ventilation system alongside improving air tightness – a home that’s too airtight without proper ventilation can lead to condensation and mould. There’s a saying in the construction industry: “build tight, ventilate right.” If you’re unsure whether your ventilation system’s performance is adequate, get it tested.
A good level of insulation is also beneficial, as air tightness is only one part of the energy-saving equation, albeit a big part.
How Can an Airtight Home Reduce My Bills?
Excess natural and uncontrolled ventilation – air leakage – means the heating required to compensate is increased. Leaks cause draughts which, to maintain comfort, have to be offset by heating rooms to higher temperatures for longer. Eliminate those draughts by improving your home’s air tightness, and less energy is needed for thermal comfort – saving money on your energy bills.
A comparatively small reduction in uncontrolled ventilation results in considerable energy savings. In other words, improving your home’s air tightness even a little can have a relatively large beneficial effect on both your energy bills and carbon consumption.
Some of the most airtight, well-insulated properties we’ve tested haven’t needed a heating system installed at all. Once a building achieves a certain level of air tightness – usually 1 m³/h⁻¹/m⁻² or under – it takes very little energy to warm up. This standard is known as Passivhaus. At that level of airtightness, combined with adequate insulation and ventilation, a dedicated heating system can be unnecessary – the building can be warmed largely by occupants’ own body heat and the excess heat from appliances. For properties like these, good air tightness doesn’t just reduce heating bills – it can eliminate them.
This is exactly the kind of problem an air test can diagnose in an ordinary home, not just a Passivhaus. One Bristol homeowner, David, struggled to get his house above 17-18°C even with the heating on constantly. A blower door test, whole house ventilation survey and thermal imaging survey traced exactly where his heat was escaping and gave him a prioritised roadmap for his budget.
Other factors
Indoor air quality in leaky houses is often poor, with higher chances of mould growth – commonly seen during demolition, where clusters of mould spores appear on the back of plasterboard. This can be prevented by building tight and ventilating right. Mechanical ventilation controls the amount of fresh air entering the property, and can also filter out pollen, dust, mould spores and airborne viruses, improving indoor air quality.
Air carries a lot of water. Air leakage can cool the inside sections of external walls, causing draughts and moisture penetrating gaps in a building’s shell is a common and costly problem. So improving your home’s air tightness doesn’t just save on energy bills – it can also help you avoid repair and maintenance costs.
Common concerns
An airtight home without adequate ventilation can reduce indoor air quality – CO2 levels can rise, and condensation can form on surfaces and windows. We regularly hear this concern from clients during testing. It’s understandable, but through experience we know you cannot build a home too airtight – you can, however, under-ventilate it.
What’s Next?
If you’re not sure how airtight your home currently is, testing is the only way to know for certain – and it’s the starting point for deciding where to focus your retrofit budget.
If you’d like to talk through whether air tightness testing makes sense for your property, we’re happy to help.
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