Scotland’s New Build Heat Standard sets the pace for zero carbon heating adoption in the UK, but what does it mean for designers and will plans for dedicated Passivhaus legislation leave the rest of us playing catch up? Stephen Cousins reports
Scottish building design is on the cusp of major change as an ambitious Heat in Buildings Bill and minimum energy standards based on Passivhaus make their way through parliament.
The New Build Heat Standard (NBHS) is the first milestone on that journey and from 1 April this year required all new homes and buildings to ditch dirty fossil fuel heating systems in favour of climate-friendly alternatives.
The NBHS is the result of changes to Section 6 (Energy Standards) of the Scottish Building Regs, which came into effect in February last year, and aims to help the country meet its legally binding target to reach net-zero carbon by 2045. Buildings are the third-largest cause of greenhouse gas emissions in Scotland.
The NBHS applies to applications for any building warrant (legal permission to start building work or convert a property), and prohibits the use of any ‘direct emissions’ heating and cooling systems, such as oil and gas boilers, or bioenergy, in new buildings. Instead, building owners must adopt systems that produce zero direct emissions at point of use, such as heat pumps, electric boilers or storage heaters, 100% hydrogen systems, solar thermal or heat networks. The latter are permitted even if they use a polluting fuel source.
The NBHS does not apply to industrial process heat, and building conversions are only covered where it is considered ‘reasonably practicable’ to install a clean heating system.
Exemptions for conversions can include situations where a zero emission heating system is already installed; where there is written evidence from a qualified heating professional that it is not technically feasible to install one; or where the installation would adversely affect the character of a listed building.
A well-designed installation can achieve an efficiency of around 350%
Forward thinking
The Scottish standard comes a year ahead of UK government plans to ban fossil fuel heating systems in all newbuild homes (non-domestic buildings are excluded) in England from 2025, under the delayed Future Homes Standard. Despite it scrapping of annual climate change targets. Wales is working to the same time frame, having already prohibited the use of gas boilers in newbuild social housing in 2021.
A wider ban on polluting boilers in all properties in Scotland is expected by at least 2028, whereas the UK government recently pushed back England’s phase-out from 2033 to 2035.
Commenting on the likely impact of the NBHS in Scotland, Mhairi Grant, co-founder of central Scotland-based architect Paper Igloo, said: ‘It will make a reasonable contribution to improving the energy efficiency of newbuilds. But as energy for heating is only part of the equation, we must view this standard in tandem with other measures, which together are essential if Scotland, and the UK, are to meet our climate targets.’
Architects designing for alternative low and zero carbon emissions heating systems need to consider factors such as building type, heating and cooling loads and the impacts on internal and external space, visual appearance and noise.
As Grant points out, it is wise to work simultaneously on improving thermal performance in new buildings above the regulatory baseline as it will maximise the efficiency of heating technology: ‘All parts of the whole should be considered together, rather than in isolation.’
Residential schemes usually go for heat pumps, air- or ground-source, as the technology is well established and can run on renewable energy. A well-designed installation can achieve an efficiency of around 350%. However, the relatively high capital cost and land requirement for ground-source works against its viability, says Andy Macintosh, associate at Feilden Clegg Bradley Studios: ‘Unless you’re doing work in the ground anyway, or you have the scale to make use of it, it’s very expensive. Every scheme I’ve worked on has looked at it and decided to do air-source.’
Air-source comes with its own challenges though; units run at lower temperatures, which may mean significantly upgrading the building fabric to cut heating demand.
Units are not compact and must be installed outside, typically at ground level for a home, or in an array on the roof of an apartment block – not ideal as the industry tries to move away from rooftop plant over access and safety concerns.
Visual noise
Air-source heat pumps work by circulating air around the outside so cannot be easily enclosed, potentially creating visibility issues for designers.
Edinburgh-based architect Fraser/Livingstone has been grappling with this issue on a listed hospital conversion into flats. The prospect of having separate timber huts containing an air-source heat pump outside every front door would have ruined the historic feel, says co-founder Malcolm Fraser, so the studio is ‘trying very hard to get heat pumps into a communal location, with bin stores and bike storage’ – which increases the expense of underground pipe work.
Because of this, communal air-source heat pumps have been placed at the front of apartments at Feilden Clegg Bradley’s Brabazon Phase 2 apartments in Bristol, away from communal gardens at the rear.
Large-scale deployments, combined with electric vehicle charging, raise issues when masterplanning developments, says Macintosh: ‘We’ve seen a few meet problems where there isn’t network capacity so they’re having to deliver more substations, or even a primary substation on bigger schemes.’ In England and Wales the government's grant-giving Boiler Upgrade Scheme has seen 46% year on year growth to a monthly average of 2000 a year, showing air source heat pumps are making some headway in the consumer market.
Looking beyond heat pumps, there’s increasing interest in ‘ambient loop’ heat networks, which aim to prevent heat losses from pipework by circulating water at temperatures close to ambient conditions. Individual water-to-water heat pumps in each property then extract the energy to heat space and water. However, this emerging technology is not yet been widely deployed in the UK.
District heating systems are permitted under the NBHS and require few alterations to building design, although developers have tended to shy away from the upfront investment needed to get them up and running.
‘It requires developers to set up a small energy company to sell the heat so they can reap back the investment made,’ says Fraser. ‘Although the guaranteed payback is a fairly easy thing to set out the balance sheet for, it’s just not the sort of thing developers, or even councils, like to do.’
Flag bearer
The NBHS is flag bearer for a swathe of building performance legislation currently making its way through the Scottish Parliament. Ministers are consulting on a separate Heat in Buildings bill, intended to introduce new standards for energy efficiency and heating for homes and buildings.
Furthermore, a version of the Passivhaus standard is expected to enter the statute books in December, following a 2021 recommendation from the Scottish government’s Climate Assembly that ‘within the next five years, all new housing is built to Passivhaus standards (or an agreed Scottish equivalent)’. This ground-breaking proposal is being fleshed out via another review of energy standards within building regulations and will consider standards for new homes and new non-domestic buildings.
Architects working in Scotland are supportive of the government’s drive to tackle climate breakdown. As Grant explains, a Scottish Passivhaus equivalent for all new builds would be ‘world leading legislation’ and ‘a chance to set ourselves apart and lead the rest of the UK and beyond forward towards a more equitable, low-energy future.’
However, questions remain over the detail of the regulation and if it will be sensible and achievable. ‘I’m concerned that most new homes, even best practice Passivhaus ones, are essentially toxic polythene bags reliant on an obsession with air-tightness,’ says Fraser, who has called on ministers to focus on principles of healthy building, such as making walls vapour-open and using natural insulation like hemp or sheep’s wool.
Jo Dunwell, associate at the Edinburgh studio of Bennetts Associates, points to the need for legislation to look beyond building performance and factor in whole-life carbon. ‘Standards for calculating embodied carbon exist, such as new guidance developed by the UK Green Building Council, but they are not mandatory. We’re not going to be able to keep below the 1.5ºC climate target without involving embodied carbon because [as operational energy comes down] all the energy is being used up front on projects, and if we don’t control that we’re not getting the full picture.’
Read all about the RIBA's 2030 Climate Challenge and work on the Net Zero Carbon Building Standard.