10 ways NZEB is revolutionising Irish home building

Since the end of 2019 Ireland has required that all new homes be nearly zero energy buildings (better known as NZEBs), in line with EU law. The move to NZEB is one of the biggest changes to Ireland’s building regulations in the past 20 years.

So what exactly does NZEB mean? Well, under the EU’s Energy Performance of Buildings Directive, each country has a certain amount of freedom to define its own version of the standard, based on its local climate. Ireland’s interpretation states that NZEB dwellings should have a maximum primary energy demand of 45 kWh/m²/yr. The standard is different for non-domestic buildings, but in this blog post we will mostly focus on dwellings.

In Part L of Ireland’s building regulations, which covers energy efficiency, standards are set against the 2002 version of the regulations. So for example, 2007’s regulations required dwellings to use 40% less energy than 2002, 2011’s code required dwellings to use 60% less compared to 2002, and finally 2019’s version of Part L — which defined NZEB and wrote it into law — required 70% less.

So while the introduction of NZEB to Part L was just the latest in a series of gradual improvements, it was also one of the most ambitious to date, and it has already led to all sorts of changes in how Irish homes are built, heated, and ventilated.

Here are ten ways NZEB has already changed the Irish building industry forever.

1. Homes are becoming more energy efficient. One of the best ways to see how construction in Ireland is changing is to look at SEAI’s BER Research Tool, a database of every building energy rating (BER) published since the government introduced the label in 2007. In-depth analysis of this data performed by Jeff Colley at Passive House Plus magazine reveals that the average primary energy demand of new homes in Ireland dropped from 86 kWh/m²/yr in 2012 (a mid B1 rating), to 50 kWh/m²/yr in 2019, and it has now fallen even further with the introduction of NZEB to just 41 kWh/m²/yr, an A2 rating, less than half what it was a decade ago.
    
2. Heat pumps are taking over. Analysis by Passive House Plus also reveals that a whopping 93% of new homes built to the NZEB standard now use a heat pump as their main form of space heating. Gas boilers are down to just 4% of new dwellings. This is a huge decline from 2018, when gas was the main space heating fuel in over half of new homes.
    
3. Homes are getting more airtight. Between 2017 and early 2021, the average airtightness of new Irish dwellings improved from 3.85 to 2.55 m³/hr/m². While previously housebuilders might have prioritised installing more insulation or renewable energy systems to meet Part L, tightening regulations means more housebuilders are now focusing on fabric-first measures like airtightness. Leaky homes are a thing of the past.
    
4. The industry is upskilling like never before. With NZEB now a requirement for all new buildings in Ireland, there has been a major drive to train builders, plumbers, plasterers and all types of tradespeople to deliver the standard — as well as to upskill those on the design side of construction, like architects and engineers. The Irish government recently launched four new retrofitting centres of excellence, while there has been a growth in NZEB-specific training too. Waterford Wexford Education and Training Board offers courses in NZEB fundamentals, NZEB ventilation, and NZEB for various trades, including plumbing and carpentry. Waterford Institute of Technology, meanwhile, is offering a new certificate in NZEB design.
    
5. Natural ventilation is becoming a thing of the past. Ireland’s latest version of Part L advises the use of mechanical ventilation in dwellings with airtightness of 3 m³/hr/m² or better, and so-called “natural” ventilation systems — such as hole-in-the-wall or trickle vents— are now in decline. While 50% of new homes were naturally ventilated in 2019, just 17% of early homes built to the NZEB standard were, as of March 2021, and 68% of new dwellings had mechanical systems such as central extract or heat recovery ventilation.
    
6. There is more quality control for ventilation systems.  Along with a new version of Part L, NZEB also saw the introduction of a new version of Part F of the building regulations, which deals with ventilation. This introduced a requirement that all ventilation systems be designed, installed and commissioned by competent persons — and then independently certified. This should help to ensure these systems deliver good air flow to homes, protecting indoor air quality, and helping to prevent dampness and mould.
    
7. Solar PV is in decline. Part L contains an obligation that dwellings must meet a certain proportion of their energy demand through on-site renewable energy, and until recently, the most common way to achieve this was with a solar photovoltaic system, often in conjunction with a gas boiler for heating. But a new calculation method, plus the falling carbon footprint of electricity in Ireland, means that heat pumps are now usually capable of meeting the renewables requirement on their own. So while over half of new homes built in 2017 had a solar PV array, they now feature in just 17% of NZEB homes as of March this year. While this might look like a negative trend, it probably means that housebuilders are first meeting the regulations through building fabric measures and sensibly specified heating systems, rather than primarily through “bolt on” renewable energy technology. Of course, the market share for solar PV is likely to grow quickly again if Ireland introduces a renewable energy feed in tariff.
    
8. More people are installing triple-glazing: the average window U-value has fallen from 1.21 in 2018 to 1.67 for new NZEBs, indicating that more housebuilders are installing triple rather than double glazing, as the cost of triple-glazing falls.
    
9. Public awareness of fabric-first building is on the rise. As energy efficiency rules have tightened, and NZEB has become the norm, the general public has become more aware of concepts like airtightness, ventilation and the passive house standard. Those working in the industry report that customers are much more informed and educated, and more likely to recognise and call out energy inefficient design and poor workmanship.
    
10. Passive house is becoming more popular. The advent of NZEB has made the passive house standard more popular, too, according to two passive house certifiers we spoke to while researching this article. Complying with NZEB usually means choosing fabric-first measures like continuous insulation, airtightness and mechanical ventilation – the very same principles that are at the heart of the passive house standard. So more and more developers and self-builders now see little cost difference between building to NZEB and going that bit further and building to the passive house standard. One passive house certifier also told us that because the Irish building regulations don’t deal with overheating well, more clients are now putting their projects through the passive house software, PHPP, to help ensure summer comfort — even if they don’t plan to have their building certified.

As we have seen, NZEB has changed the way we build in Ireland, with a growing focus on fabric-first principles like airtightness and ventilation, and the decline of fossil fuel heating. We’re sure that the industry will continue to evolve over the coming years too, and we look forward to seeing what further changes are in store.

Can you suggest any other ways in which NZEB is changing the way we build in Ireland?