by Ruairi Kay
For decades, our housing priority in Ireland has been entirely about survival in the winter: keeping the cold, wind, and damp out while staying cosy inside. But is that about to change? With recent extended heatwaves, we are all looking at ways to keep cool, especially if this trend of warmer summers is here to stay.
Modern and retrofitted Irish homes tend to be well-insulated and draught-free, which is great for keeping warm. But when a heatwave hits, those very same tight envelopes can trap heat indoors, turning well-insulated living rooms into stuffy hotboxes. The good news is that you do not have to choose between a freezing house in January and a sauna in July, (not the nice mobile ones!). By combining smart passive design, modern inverter-driven cooling technology, solar power, the right choice of insulation, and a sprinkling of common sense, you can keep your home comfortably cool and your energy use low.
One of the common misconceptions among self-builders and renovators is that highly insulated homes will turn into an oven during the summer months. In reality, thermal insulation acts as a two-way shield. It stops heat from escaping your living room in the depths of winter and keeps blistering midday summer heat from penetrating your roof and walls. However, not all insulations perform equally when the sun beats down, which comes down to a physics concept called decrement delay.
Decrement delay measures the time it takes for heat from the outside air to travel through a building material and reach your interior rooms. Lightweight insulations, like standard expanded polystyrene or foil-backed PIR boards, have low thermal mass. Heat from outside can penetrate relatively quickly, often in just three to four hours, meaning the afternoon sun hits your living space just as evening arrives. Conversely, high-density, natural materials such as wood-fibre, hemp, or cellulose act like a thermal sponge. Because of their mass and specific heat capacity, they can boast a decrement delay of eight to twelve hours. By the time solar heat finally works its way through a wood-fibre roof insulation layer, the sun has gone down, the night air has cooled, and you can easily ventilate the heat back outside. If you are building or upgrading your roof in West Cork, choosing high-decrement materials is your first line of defence against summer overheating.
Another key factor in keeping heat out is the amount and orientation of your glazing and, to a lesser extent, the specification of the glass itself. While less relevant for retrofits, good architectural design can eliminate the need for active cooling entirely if you are building from scratch or even extending. Windows are the primary culprits for solar heat gain, so it pays to consider whether all that south-facing, floor-to-ceiling glass is really necessary. South and west facing glass needs external shading, such as deep roof eaves, brise-soleil architectural fins, or external roller blinds or shutters, because once sunlight passes through a window pane, the heat is trapped indoors. Design your windows to allow cross-ventilation, and consider glass specifications carefully. Triple glazing generally allows less solar gain than double glazing, and special low-solar-gain coatings can further inhibit heat on exposed elevations. High-level windows or automated roof skylights let trapped hot air escape via the stack effect at night, drawing fresh, cool breezes through the lower floor, a method we have been using to cool our own home in the evenings over recent weeks. Finally, incorporating exposed concrete, tile, or stone floors gives your interior a thermal mass heat sink to absorb daytime heat, though caution is needed, as combining high thermal mass with overglazing can release excess heat overnight and worsen overheating. If you are building a new house, assessing overheating risk is just as important as checking energy ratings and heat loss.
When passive measures are not enough, mechanical cooling steps in, though systems should always be a last resort. There are several options based around heat pump technology. If you have underfloor heating paired with a ground-source or air-source heat pump, it can often be adapted for cooling. Ground-source geothermal systems are preferable because cooling can be done passively via a small heat exchanger that takes water directly from the ground loop to cool the underfloor circuit, bypassing the compressor. The only energy used is by the circulation pump; a clever, low-cost solution that I have heard anecdotally has reduced indoor temperatures by about four degrees in several West Cork homes this summer! Reversible air-to-water heat pumps can also supply cold water, though this requires running the compressor and consumes more electricity. Neither method works with standard metal radiators, as they lack sufficient surface area and will collect condensation that drips onto floors and causes corrosion.
Alternatively, air-to-air heat pumps operate like modern European air conditioning, using an outdoor unit to feed indoor room units. These have not traditionally been popular in Ireland due to our historic familiarity with wet radiator systems, lower SEAI grant support and historical lack of need. They do however work exceptionally well for both heating and cooling in smaller retrofitted properties without an existing wet distribution system and I have been involved in a few projects like this.
All modern heat pump systems utilise inverter technology. Unlike older air conditioners that blared at full power until hitting a temperature target and then shut off completely, inverter-driven compressors act like a dimmer switch. Once the target temperature is reached, the compressor slows down smoothly to maintain a steady climate while drawing minimal electricity. When paired with a rooftop Solar PV system, the economics align. As I have often told clients, while solar power rarely matches winter heating demand, peak cooling needs occur on the sunniest days when panels generate maximum output. Instead of drawing grid power, your home essentially runs on free West Cork sunshine.
For homeowners looking to fund these upgrades, government support is structured around targeted schemes. The SEAI Warmer Homes Scheme provides fully funded energy upgrades for low-income homeowners receiving qualifying welfare payments. A Medically Vulnerable Scheme also offers fully funded solar installations for households with registered medical needs requiring heavy power use. For general homeowners, standard SEAI grants offer up to €1,800 alongside zero percent VAT on solar panel installations, up to €12,500 for heat pumps providing space heating, and up to €2,000 to insulate attics with cellulose to combat summer heat.
As always, if you would like to get in touch about anything discussed here or your own retrofit project, feel free to reach out to Ruairí at [email protected].
