Brigid Browne: Does an A-rated home get stuffy?

Simple solutions like opening windows at cooler times, using blinds, or improving ventilation can help bring your home back to the comfortable level you expect.

Modern air-conditioning systems, particularly air-to-air heat pumps, use relatively little electricity.

Hi Brigid,

Our house could probably do with a retrofit, but before we advance that project, I have a couple of questions for you. We were in our friend’s new ‘A’ rated home recently and it was really uncomfortable due to the heat. They are now talking about getting an air-con system in. But isn’t that defeating the purpose of an ‘A’ rated home if the key objective is to lower energy usage and costs? My other issue with ‘A’ rated homes is because they are air-tight, they are stuffy, with no fresh air circulating in them. Does this not raise health issues for the people living in them? I know older buildings can be draughty and often cost a lot more to heat than modern ones, but there is no shortage of fresh air in them. So, is it better to try aim for a happy medium rather than going completely airtight in search of ‘A’ rated nirvana?

Regards, Garrett

Hi Garrett,

Your query allows me to set the record straight on the whole airtightness and stuffy internal environment question.

How can an ‘A’ rated house be uncomfortably warm?

What you’ve likely experienced has been given the term ‘overheating’, which is an increasingly recognised challenge in modern, highly insulated homes.

Overheating is when indoor temperatures become uncomfortably high, especially during warm weather. The very features that make an A-rated house energy efficient, such as high-performance windows, excellent insulation, and airtightness, are designed to keep heat in. Add to this south- and west-facing windows and glazed sliding doors with larger window to wall ratios, appliances, and even people — then bring a heatwave into the mix and the result is overheating.

Overheating also happens in non-residential buildings. There are some office blocks that become ‘sick buildings’ because many employees can’t cope with the heat created by too much glass and they call in sick or work from home during certain times of the year.

Simple solutions like opening windows at cooler times, using blinds, planting shrubs and trees where they offer shade but will not impact foundations, or improving ventilation can help bring your home back to the comfortable level you expect.

Good building design

Installing air conditioning doesn’t automatically defeat the purpose of an A-rated home. Modern air-conditioning systems, particularly air-to-air heat pumps, are remarkably efficient and use relatively little electricity compared with older systems. If powered by electricity from renewable sources, such as PV solar panels, their environmental impact can be quite modest.

Ideally, however, overheating should be addressed primarily through good building design before relying on mechanical cooling.

Your second question touches on one of the biggest misconceptions about modern low-energy homes. Airtightness versus air quality.

To start with, airtightness and ventilation are two completely different things. Airtightness simply means reducing uncontrolled and undesigned air leakage through gaps around windows, doors, floors and walls.

Older houses often have plenty of ‘fresh air’, but unfortunately much of it arrives through cracks and gaps that also allow valuable heat to escape.

You might have read previous articles I’ve written answering questions from some readers who live in old houses where they sit in uncomfortable conditions because of uncontrolled and undesigned air entry and leakage, which cause temperature fluctuations.

This uncontrolled ventilation is inefficient, unpredictable, and often brings with it cold draughts, moisture, and outdoor pollutants. Leakage costs money, wastes energy (constantly reheating space), not to mention gives us cricks in our necks and cold toes.

Ventilation

A-rated homes are designed and built to minimise these unwanted leaks. Importantly they are also designed with planned ventilation systems that provide a continuous supply of fresh air.

Many new homes use mechanical ventilation with heat recovery (MVHR) systems. These systems continuously extract stale, moisture-laden air from kitchens, bathrooms, and utility rooms while supplying filtered fresh air to living rooms and bedrooms. Importantly, they recover much of the heat from the outgoing air and transfer it to the incoming fresh air. The result is a constant supply of fresh, filtered air without the large heat losses associated with opening windows on a cold day. These systems can actually improve indoor air quality compared with many older homes.

Maintenance

That said, no system is perfect. Like any piece of equipment, mechanical ventilation requires regular maintenance. If I had a euro for every time I come across filters that haven’t been changed, I could go on a city break six times a year. Designers have huge responsibility here in that it’s critical that those parts of any system requiring maintenance are located with easy access for homeowners and maintenance providers. When something is easy to get to, it has a higher chance of being cleaned.

Filters need to be cleaned as per manufacturer’s instructions, or, when you get familiar with the system, you might change them more regularly. Ducts should remain clean, and systems should be correctly balanced, so each room gets the intended airflow. When systems are designed, installed, and maintained correctly they help reduce dust, condensation, mould growth, and allergens while maintaining comfortable humidity levels. If neglected, performance can suffer and indoor air quality will deteriorate.

Stale air is a legitimate thing for sure, but it is more likely to do with lack of maintenance and understanding of mechanical systems than airtightness. Airtightness shouldn’t exist where there is no ventilation. Ventilation is more efficient where there is airtightness.

Where you are renovating older properties such as stone buildings, airtightness is a huge advantage and most of this may be achieved with natural lime plasters and renders.

These plasters and renders tend to be thickly applied, are relatively flexible and they allow vapour transfer so your building can ‘breathe’.

But as I mentioned, designed ventilation is key, be it a traditional hole in the wall or a mechanical system.

Send your home build queries here

Building surveyor Brigid Browne

• Brigid Browne is a chartered building surveyor and Chair of the Southern Region of the Society of Chartered Surveyors Ireland. She is the MD of Cashel-based Fortress Planning. fortressplanning.ie