We Built for Cold. Now We're Too Hot.

Irish houses were built to solve one problem: keeping heat in. For most of the last century that was the only problem worth solving, and we were not especially good at it. Then, for twenty years, we got serious — insulation, airtightness, better glazing, heat pumps, a national retrofit programme with billions attached.

It worked. And now, in August 2026, the Department of Housing is convening researchers from SEAI, the RIAI, the Irish Planning Institute and Met Éireann to discuss a problem nobody in Irish housing policy has ever had to think about.

Our homes are getting too hot.

TU Dublin puts up to 10% of the Irish housing stock at risk of overheating. Writing in The Irish Times on 2 July 2026, Lorcan Sirr put the number of people affected at 520,000.

Dr Frank Mulville's summary is the whole problem in a sentence: these are homes "designed to retain heat for winter and aren't designed for the heat we're getting this summer."

He is not saying this with hindsight. He published a warning about exactly this in Building Research & Information in 2016.

How bad is it, honestly?

Here the evidence gets more interesting than the headline, and it is worth being straight about.

A UCD study published in Energies in March 2025 examined 943 Dublin social homes and found overheating risk in moderately insulated, BER-C stock to be "minimal". That is a real finding and it cuts against the panic.

But the same study found mean living-room temperatures rising steadily with energy rating — from 20.25°C in G-rated homes to 22.46°C in A-rated ones. The better the house performs in winter, the warmer it runs in summer.

And the study exposed something that ought to be better known: whether a home "overheats" depends enormously on which yardstick you use. Applying three different recognised standards to the same houses produced overheating rates of 0.4%, 4%, and 41%.

Same buildings. Same data. A hundredfold difference in the answer, depending on which threshold you pick.

So the accurate version is not "Irish homes are overheating". It is that the risk is concentrated — in deeply retrofitted homes, in single-aspect apartments, in top-floor flats — and that we have not agreed how to measure it.

The gap in the regulations

Which leads to the genuinely awkward fact.

England has had a mandatory overheating standard since 2022 — Part O of the building regulations, which requires new homes to be assessed for summer overheating and to limit solar gain.

Ireland has no equivalent.

Ireland's Zero Emission Building standard takes effect on 1 January 2028, and as things stand it has not yet set indoor temperature or humidity parameters. Asked about it, the Department of Housing's position is that "work is ongoing."

We are, in other words, still building homes to a standard that regulates heat retention and not heat gain, in a climate that has started producing the second problem.

The engineering case for cooling without air conditioning.

Meanwhile, the retrofit itself is behind

The programme that created this situation is also, on its own terms, badly off pace.

The ESRI reported in March 2026 that Ireland had completed roughly 58,000 deep retrofits against a target of 500,000 — 11.5%. Heat pumps are further behind still: around 14,000 against a target of 400,000, or 3.5%.

SEAI's own 2024 report does not dress it up, describing the heat pump target as "extremely difficult to achieve."

The 2026 supports are substantial — a heat pump grant of up to €12,500 from 3 February 2026, a new windows and doors grant from 2 March, a budget of €640m and a target of 73,000 upgrades. Money is not the constraint.

The number that explains the heat pump problem

A heat pump's economics depend on one ratio: the price of electricity against the price of the fuel it replaces.

SEAI's own fuel cost comparison, dated 1 July 2026, puts electricity at 34.38 cent per kWh and gas at 13.00 cent. A ratio of roughly 2.6 to 1.

Now, a heat pump is not a one-to-one swap. At a seasonal performance factor of 3.5 it delivers heat at about 9.82 cent per kWh, against roughly 18.6 cent from a gas boiler. On those figures it wins comfortably.

But that depends on installation quality, on the house being properly insulated, and on the ratio holding. And Ireland's ratio is the worst in Europe to be doing this in: Eurostat put Irish household electricity at €40.42 per 100 kWh in the second half of 2025 — the highest in the EU, around 40% above the average.

SEAI's Ciaran Byrne named it directly: "the big one at the moment is the cost of electricity."

Ireland is asking households to electrify their heating in the most expensive electricity market in the Union.

What a heat pump retrofit actually involves in an ordinary terrace.

How everyone else stays cool

Southern Europe has been solving this for centuries, and almost none of it involves air conditioning.

The Mediterranean answer is external — shutters, awnings, deep reveals, blinds fitted outside the glass. This is the single biggest thing Irish homes get wrong. An internal blind stops light after the heat is already inside; an external one stops the heat at the window. Add thermal mass to absorb the day's gain, and night ventilation to purge it.

The behavioural half matters too: closing up during the hottest hours rather than throwing everything open, which is the Irish instinct and precisely backwards on a hot afternoon.

Spain has gone further and legislated. Government rules have limited air conditioning settings in commercial premises and required shops to keep doors closed while cooling — a policy response Ireland has never needed and may.

Spain legislating on cooling — the kind of measure Ireland has never required.

Why this is a health story, not a comfort story

It would be easy to treat overheating as a first-world irritation. The historical record says otherwise, and it says it about Ireland specifically.

Research by Healy published in 2003 found Ireland's excess winter mortality ran at 21% — joint second-worst in the then EU-14, despite Ireland having one of its mildest climates. Countries with far colder winters did far better. The difference was housing: thermal efficiency, or the lack of it.

That is the strongest possible argument for the retrofit programme, and it is why this article is not an argument against insulation. By 2002–11 the figure had fallen to 13.9%. Warmer homes saved lives.

But the same physics runs both ways. A study in Nature Medicine attributed 62,775 deaths in Europe to heat in 2024. Germany's Robert Koch Institute reported on 20 August 2026 that summer 2026 had produced a record of roughly 14,000 heat-related deaths.

Ireland's mild climate did not protect it from cold. It will not automatically protect it from heat either.

What to actually do

If your house gets uncomfortable in summer, the interventions in rough order of effect and inverse order of cost:

• Shade the glass from outside. External blinds, shutters or awnings on south and west-facing windows. Nothing else comes close.
• Purge at night, close up by day. Open everything when the outside air is cooler than the inside air, and shut it when it isn't.
• Check your ventilation actually works, particularly if you have been deep-retrofitted. Airtightness without working ventilation is the specific combination that causes trouble.
• Be sceptical of air conditioning as a first move. It is expensive to run in the EU's dearest electricity market, and it exports your heat to the street, which is how cities get hotter.

And if you are building or buying new: ask what the overheating assessment says. In England you would be entitled to one. Here, for now, you have to ask.

A note on the sourcing

Grant figures and fuel costs are from SEAI and are dated, because they change — the heat pump maximum quoted applies from 3 February 2026 and the fuel comparison from 1 July 2026. Retrofit progress figures are the ESRI's. Electricity price comparisons are Eurostat's for the second half of 2025. The overheating research is peer-reviewed and, as set out above, its findings depend heavily on which standard is applied.

One thing this piece does not do is tell you your house is dangerous. The best Irish evidence says the risk in typical, moderately insulated stock is currently low. The concern is specific, and it is about where the building stock is heading rather than where most of it is now.

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