Scotland’s move toward a Passivhaus standard

From December 2024, all new housing in Scotland will be built to the highest energy efficiency standards: a Scottish Passivhaus equivalent. Right now, no one knows exactly what that means.

Passivhaus is, in short, the gold standard for energy-efficient homes. According to physicist Wolfgang Feist, co-founder of the concept: “The heat losses of the building are reduced so much that it hardly needs any heating at all.” Certified houses are built with high-quality insulation, triple glazing, insulated frames, mechanical ventilation, and airtightness levels around twenty times higher than a typical UK build. These homes are so good at retaining heat that the sun, inhabitants, and household appliances fulfil most heating needs – hence ‘passive house’.

The standard was developed by Feist and structural engineer Bo Adamson in the early 1990s, with the first certified homes appearing in Germany soon after. It is managed by the Darmstadt-based Passivhaus Institute, an independent non-profit research body. The concept is well established and well regarded, but so far there are few certified houses in existence today (approximately 38,000 units as of January 2023).

The ongoing push towards decarbonisation could change everything for Passivhaus. Heating the UK’s exceptionally draughty housing stock contributes 14 per cent of national carbon emissions, so improving its energy efficiency is broadly seen as an important and easy step towards reaching net-zero emissions by 2050. This requires both retrofitting existing housing stock and building new homes to higher energy efficiency standards.

Built Environment–Smarter Transformation (BE-ST) – which connects industry, government, and academics in an effort to make the Scottish construction industry more sustainable – has observed a recent surge of interest in the standard. Caitriona Jordan, head of retrofit, said that while BE-ST had previously been working hard to promote its Passivhaus training, “now contractors and designers are knocking at our door and saying: we want to get involved with this, we want to upskill!”

There is strong public support for Passivhaus – at least, among those who know what it is. In 2021, the Scottish Climate Assembly voted in favour of a recommendation for all new housing to be built to the standard or an equivalent by an overwhelming majority (97 per cent). This prompted a Labour MSP, Alex Rowley, to introduce a Private Member’s Bill that would make the standard or equivalent mandatory for all new domestic housing. His proposal attracted support from the Scottish government, which in turn promised to introduce secondary legislation (a much less time-consuming process than seeing a Private Member’s Bill through Parliament) to bring it into effect by the end of 2024.

This will create a ‘Scottish equivalent to the Passivhaus standard’ for all new-build housing.

The Scottish government’s pledge is a major win for Passivhaus. A number of local governments have endorsed or implemented variations on the standard – Dún Laoghaire-Rathdown County Council in Ireland, Brussels in Belgium, Heidelberg in Germany, Vancouver in Canada, among others – but this is a first for a national government. While few have criticised the ambition, there are practical concerns about how the standard might be implemented.

Some Scottish housebuilders argue that – given cuts to Scotland’s Affordable Housing Supply Programme – this is already a challenging time for the sector, and the demanding new standard could hamper efforts to build at the speed and volume a housing crisis would generally demand. There are calls for the introduction of the standard to come with significant support to ensure that it is affordable. This is no unreasonable demand – the higher upfront cost of Passivhaus has long been a barrier to adoption. The Scottish government will be expected to show that it means business, then, by setting aside sufficient funding to help meet these costs.

This could be money very well spent. The relative cost of Passivhaus is falling, thanks to tightening building regulations, increased manufacturing of high-quality insulation, and other factors (a 2019 report by the Passivhaus Trust estimated that costs were around eight per cent higher than for comparable houses constructed to building regulation standards). The higher upfront cost is offset by heating bills being slashed by up to 90 per cent – more appealing now than ever.

Schematic diagram of Passivhaus

Passivhaus features seek to maximise a building’s energy efficiency.

Image credit: John Gilbert Architects

Sustainability and affordability are not the only benefits of Passivhaus – the standard also aims to create healthier living environments, with improved ventilation eliminating condensation and mould. In November 2022, a coroner attributed the death of a two-year-old child, Awaab Ishak, to ‘chronic exposure’ to mould in his family’s Rochdale flat, prompting outrage about the toll that low-cost, low-quality social housing can take on occupants. The tragedy entrenched agreement across much of the political spectrum that the housing crisis is about more than just numbers. “In order to solve the housing crisis, you’ve got to address quantity, but you’ve also got to address the quality of what gets built,” says Dr Charles Goode, an expert in planning at the University of Birmingham. “You can’t artificially separate the environmental crisis from the housing crisis; they need to be solved in tandem.”

The potential of a Passivhaus equivalent to help resolve several interconnected problems – climate change, the housing shortage, wealth and health inequality – is being acknowledged now at the highest levels. The Scottish government’s minister for zero-carbon housing commented earlier this year that the new standard “is not just about reducing carbon emissions […] it is also essential if we are to meet the cost-of-living challenge”.

There is plenty of concern about the UK’s ageing housing stock – draughty Victorian terraces in need of retrofitting to cut gas consumption. But new housing stock also gives cause for concern. According to a 2022 report from the Business, Energy, and Industrial Strategy select committee, heat loss from new-builds can be 50 per cent higher than expected. This is possible because building regulations are based on a model building design, with little requirement for developers to demonstrate their buildings meet the standard in practice.

In contrast, Passivhaus developers must prove their buildings meet the standard in order to receive certification. This requires designers and contractors to follow a distinct Passivhaus-approved process with performance assurance at its core – a process which even its most enthusiastic supporters agree is “quite intense”.

The success of Scotland’s policy could hinge on the dry but critically important question of performance assurance. According to Jon Bootland, chief executive of the Passivhaus Trust: “In order to get to the Passivhaus equivalent standard by the end of 2024 and have that implemented, the performance assurance question is absolutely key.” The Scottish government has indicated that it recognises the importance of performance assurance, stating that its Passivhaus equivalent will not only raise targets but also – in the spirit of the original standard – improve performance assurance so the buildings can be trusted to “deliver the performance sought in practice”.

This calls for a rapid change in culture. Designers and contractors will need training to work with the new standard (whatever it contains) and there must also be a major drive to train certifiers. In addition to the Passivhaus Institute itself, there is a small handful of bodies in the UK qualified to certify to that standard – the process of training someone in Passivhaus certification is far from trivial. Already, architect Jennifer Rooney of ECD Architects has noted a shortage of Passivhaus certifiers: “Many of them have massive workloads. Sometimes they’re not even returning quotes now because their books are full,” she says. “And that’s without the [new] standard. I think it’s a great idea the Scottish government are going to build this set of regulations, but good thinking about how certification is going to happen is really important.”

This upskilling effort must begin soon if the standard is to be implemented on schedule. It is somewhat on hold, however, due to the fact that (as of the time of writing, March 2023) it is not known exactly what the Scottish Passivhaus equivalent will contain. Bootland cautions: “If the Scottish government develops a standard that diverges significantly from the international standard, then tries to implement that at the end of 2024, that would be quite tricky because they won’t have the training in place, or the people, to do the quality assurance.”

There could be mere weeks left for the Scottish government to finalise and publish its standard if training is to begin in good time. Delays could compromise performance – a real lost opportunity, given that closing the performance gap, is what really sets Passivhaus apart. A realistic risk is that, from 2024, new houses in Scotland are built to equivalent targets without an equivalent performance assurance process. A Passivhaus-certified home would remain a premium product.

Behind closed doors, there is a multitude of other criticisms being lobbed at the Scottish government’s plan. Some groups argue that electrification of the grid should be its priority; some point to the difficulty of acquiring materials which might need to be imported from Europe; some say – not incorrectly – that introducing the standard for new-builds will barely make a dent in the energy efficiency of Scotland’s housing stock overall. Industry group Homes for Scotland told Scottish Housing News that: “New homes are only a small proportion of the overall housing stock and are already highly energy-efficient […] the focus must be on retrofitting the bulk of existing properties that are predominantly responsible for residential emissions.”

The adoption of a Passivhaus equivalent could have wide-ranging benefits, but it is just one element in a massive nationwide effort to reach net-zero carbon emissions by 2045. It is notable that, despite practical concerns, there are essentially no objections to the principle of raising energy-efficiency standards for new builds. The Scottish government must now focus on developing an effective and practicable standard and do so with enough time for the industry to prepare. “It’s a big step change,” says BE-ST’s Jordan. “But I think if they get given enough time, enough information and guidance, [stakeholders] will be able to work to those standards. The direction from the Scottish government needs to be clear. Maybe initially they may be resistant, but once they understand the correct process and procedure and what they need to do to achieve it, everything else will start to fall into place.”

In the meantime, the UK government – amid its Future Homes Standard consultation, which could see building regulations for England and Wales brought into close alignment with the Passivhaus standard – will surely be watching closely.


A first for Scottish social housing

A housing development in Drymen, Stirlingshire, recently became Scotland’s first social housing development to receive Passivhaus certification. The project was driven by Hanover Housing Association, which, according to Jennifer Rooney of ECD Architects, who worked on the project, wanted to “do something pretty special” for its first Scottish site.

Initially, Hanover looked at retrofitting the existing post-war homes, which can be done to a separate certification issued by the Passivhaus Institute. At the time, however, there was limited public funding for retrofitting projects, so it was decided that it would be most cost-effective to demolish and rebuild them.

To ensure that the homes could be built in a cost-effective manner suitable for social housing, ECD Architects used the Passivhaus Planning Package – effectively a spreadsheet into which all the details of a design are entered, outputting whether or not that design meets the standard. This allows designers to make adjustments, whether for design preferences or budgetary needs, and check that the building is still acceptable. “Using it as a tool for the design and construction process is really critical,” said Rooney. “If your heat demand is too low compared to the target, perhaps you’re over-specifying things. You can pare things back, so you still meet the standard but you’re not tipping the budget too far.”

According to ECD’s design, 15 new houses were built with solar panels, mechanical heat recovery ventilation, triple-glazed doors and windows, and additional in-wall insulation. They received Passivhaus certification in December 2022.

The new homes in Drymen will require significantly less energy for heating than the average new-build.

The new homes in Drymen will require significantly less energy for heating than the average new-build.

Image credit: Mcateer Photo

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