The UK Net Zero Carbon Building Standard pilot
Following the launch of the UK Net Zero Building Standard, Piers Sadler considers how the standard may be applied and how it fits with Passivhaus;
I welcome the introduction of the Standard, particularly its ambition and breadth and the move from ‘net zero buildings’ to ‘net zero aligned buildings’. In my reaction below I am trying not to be skeptical about the details, instead I’d like to draw out some useful implications and ask some helpful questions.
The new pilot of the UK Net Zero Carbon Buildings Standard (the Standard) was published on Tuesday 24th September 2024 and the Standard launch webinar was yesterday. I was waiting until after the webinar to give my reaction to the Standard.
I’m not going to discuss the limits in detail here, only the implications, so my response below assumes that the reader is broadly familiar with the Standard. As a reminder the following graphic illustrates the main criteria within the Standard. Importantly, the operational energy and whole life carbon targets are based on monitoring for a 12 month in-use period and no claim can be made related to compliance with the Standard until the monitoring period is complete.
What I like
I support the use of an Upfront Carbon metric as well as the intention of bringing in limits for Whole Life Embodied Carbon. The ramping down of the Upfront Carbon targets over time makes sense, reflecting a changing energy landscape with reduced carbon intensity of the electricity grid, in particular. The initial Upfront Carbon targets are not too onerous for most building types, which will help capture more buildings initially.
I think EUI is the right metric for Operational Energy. By using energy instead of carbon here, the Standard does not have to address the changing nature of the energy supply. Our testing shows that Passivhaus buildings will not automatically pass the EUI target. This demonstrates the ambition of these targets, which I support. In many cases buildings will have to go beyond the Passivhaus Primary Energy Renewable requirements to meet the Standard by delivering more efficient building services and equipment.
The Heating Demand metrics are suitably demanding, but do reflect the challenges for small single family homes. All the key elements of the Passivhaus Standard will be required to meet these metrics, including airtightness and heat recovery ventilation.
We support the Fossil Fuel Free, District Heating and Refrigerants metrics.
Monitoring of in-use performance will ensure that actual performance is what matters, rather than a theoretical prediction (see below for counter arguments). Introducing in-use monitoring is welcomed as it should help improve the operation of our buildings.
We hope that, as with the Scottish Futures Trust, which has resulted in the construction of lots of Passivhaus schools, clients will be looking for methodologies which ensure that in-use performance is locked in by the design and construction processes. The Passivhaus Standard is the only methodology with a track record of achieving this and therefore we might expect to see increased uptake of Passivhaus.
Some questions and doubts
How could the Standard be used to encourage alignment with 1.5C of warming? At present it is a voluntary standard, but there is presumably an intention to see widespread uptake. The Standard could not be adopted for planning or regulation because the buildings would be long in use before it is known whether they pass or fail. There would be no practical way of revoking the permissions previously provided for non-performing buildings.
So to achieve widespread uptake does the Standard have to be associated with financial incentives both for energy efficiency in use, but also retrofit works? Government mandated incentives would be one way that widespread uptake of the Standard could occur.
Is the Standard mainly aimed at corporations and their carbon reporting? In this case maybe the incentive would be meeting company or international obligations and direct financial incentives would not be so important.
Where will responsibility for achieving the Standard fall? Owners, designers, builders, operators and occupants would all have a stake, but how could this be controlled? As a design team member, the absence of any design or construction based claims against the Standard, such as ‘This building has been designed in alignment with the Standard’ makes me feel remote from the process of achieving the Standard. When buildings are sold on completion this blurring of responsibility becomes murkier still.
How could the Standard reasonably be applied to housing? The plot from the PHI below shows modelled versus actual performance from four housing developments. For the Passivhaus developments the PHPP model results correspond approximately with the mean annual heating demand of each development. Approximately 50% of the houses in each development have higher annual heating demand than predicted by the PHPP. this is Passivhaus buildings and only heating demand.
So we can reasonably expect, if we design for a particular average energy usage, at least 50% of houses could be expected to fail. Is the expectation that incentives would skew the energy use downwards and most of these high results would not occur?
There is nothing in the Standard about comfort, indoor air quality or health, so it is possible that buildings which meet the Standard have poor indoor air quality, are cold and suffer from condensation and mould. Are there potential unintended negative consequences of the Standard in relation to occupant health and wellbeing?
Is there a potential unintended consequence of houses being designed as PV mounts?The on-site generation requirement is perhaps too onerous for single family homes, so the design of homes could be altered to maximise PV accommodation.
Final comment
The Standard is comprehensive, achievable and challenging and is welcomed as the first proper attempt in the UK of defining what a net zero building is.
There are some significant questions to be answered about how the Standard will work in practice and what will drive uptake. We look forward to hearing more about this in the near future.
It is clear that a quality assurance process will be required to give confidence in outcomes. The Passivhaus Standard is ready and waiting to help make new ‘Net Zero Carbon’ buildings happen.
The Passivhaus Standard adds the people factor, in that Passivhaus buildings are special places in which to live and work.