Retrofit redux: Catching up with A3

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In my 2015 research, I questioned whether Ireland’s retrofit strategy was fit for purpose. Cost-optimal calculations at the time recommended B2-level upgrades, often prioritising mechanical systems over the building envelope, and largely ignoring the actual condition or remaining lifespan of the buildings we were upgrading. Fabric-first strategies – proven to be effective for decades - were deemed “too expensive” in theoretical models, even though practice was already proving otherwise.

Fast-forward to 2025, and we’re finally catching up to what should have been common sense. Ireland is now moving its nZEB retrofit performance standard from B2 to A3, following a new cost-optimal review (DHLGH, 2025). This is not just a regulatory adjustment; it’s a much-needed recognition that the minimum bar was simply too low.

Over the past two years, the National Retrofit Programme has accelerated dramatically. A-rated retrofits are no longer niche – they are fast becoming the norm. In 2023 and 2024 alone, we saw a significant increase in homes achieving A-rated energy performance, supported by improved grant structures, a more capable contractor base, and a better-informed public. Notably, recent results from the National Retrofit Plan show that Community Energy and One Stop Shop retrofits are achieving an average BER of A2, far exceeding previous expectations (SEAI, 2024).

This is the result of a growing consensus around fabric-first approaches. Walls, roofs, floors, and windows form the energy backbone of any home. Upgraded properly, with adequate ventilation and airtightness, technologies like heat pumps and heat recovery ventilation systems can then perform efficiently and reliably. In poorly insulated homes, however, these systems can struggle to deliver the expected savings or comfort. It’s not about technology being good or bad. It’s about sequencing: insulate first, ventilate well, then electrify with active renewables. That’s how the best retrofit outcomes have historically been achieved.

Ireland’s retrofit market has grown substantially in both value and capability. Recent estimates place the sector at over €500 million annually, with government targets of more than 500,000 home energy upgrades by 2030, and at least 400,000 of those achieving a minimum of B2. However, under the latest cost-optimal review, the nZEB standard is now effectively defined as A3 (SEAI, 2024; Department of the Environment, Climate and Communications, 2023).

The scaling up of retrofit activity presents opportunities alongside significant risks, notably the doubling of insulation material costs in the last decade due to global disruptions and inflation, compounded by labour shortages.

Ireland's high material costs – ranking as one of the most expensive locations in Europe for a range of core construction materials like insulation (Arigoni 2022) – could erode the affordability of deep retrofit for the very households who need it most and seriously impact the Irish government’s national retrofit targets.

To ensure we’re delivering on the promise of retrofit we need to shift from modelled to measured performance. Compliance tools like DEAP or PHPP are vital, but they can’t account for occupant behaviour or unregulated loads.

In low energy homes, plug loads can account for 40 to 50 percent of total electricity consumption, yet these are rarely factored into retrofit assessments (O’Driscoll, O’Sullivan and Harrison, 2013; Menezes et al., 2012). Without real-world monitoring, we risk overpromising and underdelivering. To earn householders' trust, we need to record actual post-retrofit energy consumption across the whole building, improving design feedback loops and deepening public understanding. As we scale, it’s critical we support householders with clearer, more tailored advice.

Many don’t know where to start, what’s typical for their home type, or how to sequence upgrades within their budget. A simple roadmap, showing the most cost-effective way to reach A3 from, say, a 1970s or 1980s bungalow bliss, would empower more households to act with confidence.

Retrofit must be reframed not as an expense but as an investment – in comfort, in health, in resilience. A well-retrofitted home is warmer in winter, cooler in summer, cheaper to run, and more resistant to global economic shocks, be it COVID, the war in Ukraine, or future trade instability like Trump’s tariffs. These are not just climate actions; they are acts of personal and national resilience.

For our colleagues across the water, there’s an important question: is the UK falling behind? While Ireland is aligning its retrofit targets with an A3 minimum, the UK’s retrofit landscape remains fragmented. Ambitious in rhetoric, but inconsistent in regulation and funding, with the Future Homes Standard still under debate and regional pilots patchy at best. The UK once led on building energy performance but has lost momentum. The Irish shift to A3 could serve as both a benchmark and wake-up call, potentially reinvigorating confidence by defining minimum performance, supporting envelope upgrades, and connecting grant aid to measured outcomes could reinvigorate the sector, on both sides of the Irish Sea.

The move to A3 is not radical—it’s overdue. But it’s also an opportunity. One that must be seized with careful sequencing, informed decision-making, and robust support for households and industry alike.

In 2015, we underestimated the role of the building envelope and failed to account for the real condition of the homes we were trying to decarbonise. In 2025, we have the benefit of hindsight, real data, and a growing body of best practice. Let’s not waste it.

References (online only)

Arigoni, F., Kennedy, G. and Killeen, N., 2022. Rising construction costs and the residential real estate market in Ireland. Dublin: Central Bank of Ireland. Available at: https://www.centralbank.ie/docs/default-source/publications/financial-stability-notes/no-12-rising-construction-costs-and-the-residential-real-estate-market-in-ireland.pdf

Department of Housing, Local Government and Heritage (DHLGH), 2024. Regulatory Impact Assessment: Proposed amendments to Technical Guidance Document L (Dwellings) and Technical Guidance Document F – 2025. Dublin: DHLGH. Available at: https://www.gov.ie/en/consultation/

Department of the Environment, Climate and Communications, 2023. Review of Cost-Optimal Performance Requirements for Existing Buildings under the Energy Performance of Buildings Directive (EPBD). Dublin: Government of Ireland.

Eurima, 2023. Cost Trends in Insulation Materials across Europe 2012–2023. [online] Brussels: European Insulation Manufacturers Association. Available at: https://www.eurima.org [Accessed 5 Apr. 2025].

Menezes, A.C., Cripps, A., Bouchlaghem, D. and Buswell, R., 2012. Predicted vs. actual energy performance of non-domestic buildings: using post-occupancy evaluation data to reduce the performance gap. Applied Energy, 97, pp.355–364.

O’Driscoll, C., O’Sullivan, G. and Harrison, J., 2013. The reduction of plug loads: the next obstacle in achieving Net Zero Energy Buildings. National Maritime College of Ireland, CERC Conference, October 2013.

O’Halloran, B., 2022. Prices soar for builders as materials crisis hits. Dublin: The Irish Times. Available at: https://www.irishtimes.com/business/2022/06/27/prices-soar-for-builders-as-materials-crisis-hits/

Ó Riain, M. and Harrison, J., 2016. Cost-optimal passive versus active nZEB. How cost-optimal calculations for retrofit may change nZEB best practice in Ireland. Architectural Science Review, 59(5), pp.358–369. https://doi.org/10.1080/00038628.2016.1184130

SEAI (Sustainable Energy Authority of Ireland), 2024. National Retrofit Programme: Quarterly Report Q3 2024. [online] Dublin: SEAI. Available at: https://www.seai.ie/sites/default/files/publications/seai-retrofit-quarterly-report-q3-2024.pdf [Accessed 5 Apr. 2025].