Carrying out an air tightness test can show you where energy is being lost in your home and therefore how to reduce your bills.

Approximately 75% of the total building stock that will exist in 2050 already exists today. The UK government has set a goal to reduce national greenhouse gas emissions by 80% below 1990 levels. To achieve this target, it is clear there needs to be a substantial amount of retrofit work carried out. Including finding ways to improve existing dwellings’ air tightness.

Improving air tightness is one of the most effective ways to reduce energy use within a dwelling. It is always best to improve other aspects alongside the airtightness. This can be things like the quality of thermal insulation and efficiency of the heating system, for example.

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 (soon to be 8). This means is that no more than 10 cubic metres of air can escape per hour for every square metre of the envelope surface area. The internal air pressure also cannot exceed 50 Pascals.

Although 10 is the target to beat, most new builds need to achieve a score of 5 or lower. This is so that they can pass their SAP calculations and produce an EPC. When considering existing houses, most could safely be brought down to a 5.

‘Build tight, ventilate right’

You will need to install an adequate ventilation system beforehand if your house doesn’t already have one, as having a home that is too airtight without this can lead to some problems like condensation and mould. There is a saying used in the construction industry; ‘Build tight, ventilate right’. If you are unsure if your ventilation system’s performance is adequate, get it tested. We write about that here:

A good level of insulation would also be 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 of air leakage means that the heating required to compensate for this is increased. Leaks cause draughts which, to keep comfort levels, must be compensated for by heating the rooms to higher temperatures for long periods. If these draughts are eliminated by improving your home’s air tightness, then less energy is used to provide thermal comfort, thus saving you 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 just a little bit can have a relatively large beneficial effect on your energy bills and carbon consumption.

Our engineers have been to some properties which are so airtight, and insulated, that they haven’t even installed any heating system. This may sound crazy for this country’s climate; however, it is possible. Once a building achieves a certain level of air tightness, usually 1 m3/h-1/m-2 or under, the building will take very little heat to warm up. This building standard is known as Passivhaus. Having an airtightness this low, accompanied by adequate insulation and ventilation, means that having a heating system can be unnecessary. These buildings can usually be heated up with the occupant’s own body heat and use of appliances within, such as the excess heat from an oven. So, for properties like these, it doesn’t just reduce the occupant’s heating bills, it completely eradicates them.

Other factors

The indoor air quality in leaky houses is poor and there are higher chances of mould growth. This is seen during the demolition of houses where clusters of mould spores are found on the back of plasterboards. This can be prevented by building tight and ventilating right. Mechanical ventilation controls the amount of fresh air allowed into the property. It can also filter out pollen, dust, and mould spores, and even viruses such as Covid-19, improving indoor air quality.

Air carries a lot of water. Air leakage can cause cooling of inside sections of external walls, which can cause draughts. Damage resulting from moisture penetrating the gaps in a building’s shell is common and can be a big problem. So not only can improving your home’s air tightness save you money on your energy bills, but it could also prevent you from having to pay costly repair/maintenance bills.

Common concerns

Having an airtight home without adequate ventilation can reduce the quality of the air inside the dwelling. CO2 levels can rise to unhealthy levels and condensation can form on surfaces and windows within. Whilst performing an air test we have had queries from clients concerning this issue. While these concerns are understandable, we know through experience that you cannot build a home too airtight, you can, however, under-ventilate it.

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