Time to Go Beyond Operational Efficiency?
Passivhaus Certification Revisited
As Passivhaus-certified assessors, we are proud to have such an ultra-low emission building standard in our whole lifecycle carbon assessment (WLCA) arsenal. It has long been an effective tool in validating new developments as being constructed with the strongest principles of operational efficiency in mind. As the industry shifts its focus toward a more holistic understanding of sustainability, we question whether a change in thinking is needed, one that considers not just carbon reduction, but the wider benefits to people’s lives and the environment.
The property industry is one of the leading industries contributing to global greenhouse gas emissions, responsible for approximately one-third of total emissions. Whilst generally thought that most of these emissions derive during the initial construction of the building, i.e. the embodied carbon, in reality the situation is very different. In fact, the carbon emissions and energy consumption associated with the operational use of the building might outstrip those during construction. That is why maximising operational efficiency has become a greater focus for developers around the world.
In the UK, a large portion of the housing stock is old and poorly insulated, often relying on more outdated technologies such as gas boilers - major sources of carbon emissions. To mitigate these impacts, the industry has largely focused on improving the operational energy efficiency of buildings.
Recent updates to building regulations reflect this shift, calling for better building envelope thermal transmittance and U-values, and a general shift away from fossil fuel-based heating systems.
Passivhaus is a building standard, originally developed in Germany, that aims to achieve thermal comfort with very low energy use. Through the provision of a range of tried-and-tested solutions for achieving net-zero new and existing properties, Passivhaus has served to help accelerate the transition towards a low-carbon sector without sacrificing on occupant wellbeing.
With over 30 years of scientific research, it is a voluntary energy efficiency standard and certification system rooted in the principles of building physics, focusing on heat transfer, air movement, and energy conservation to create homes that are energy efficient, comfortable, and affordable. Whilst it has generally been thought that Passivhaus is a relatively unaffordable scheme, owing to the high up-front investiture, there is growing evidence that the cost savings over the lifetime of the building might more than compensate for the capital investment.
The standard has helped create ultra-high efficiency buildings that require little energy for space heating or cooling.
That is not to say that the standard is by any means perfect; with considerations around lifecycle carbon, biodiversity gains, circular economy, and cost-effectiveness not within the remit of the standard, there are concerns that it does not provide a holistic understanding of what has been sacrificed to achieve thermal comfort.
With over 40,000 buildings certified worldwide, Passivhaus has been a driving force behind the progress toward greater operation efficiency and has transformed how we think about energy usage. However, is this enough to tackle the broader carbon challenge?
Figure 1: Schematic representing the 5 key principles of Passivhaus. 1. Thermal Insulation. 2. Passive House Windows. 3. Ventilation Strategy. 4. Airtightness. 5. Thermal Bridge Reduction.
Getting Certified
Passivhaus certification can help ensure that buildings achieve exceptional levels of operational efficiency, relying on airtightness, high thermal insulation, high-performance glazing, efficient mechanical ventilation with heat recovery, and thermal bridge-free construction. Together, these principles create buildings that require minimal energy for heating and cooling while improving comfort.
In order to gain Passivhaus certification, developers must go through a rigorous design process, in particular with modelling from the Passivhaus Planning Package (PHPP), a design tool issued by Passivhaus that must be used to gain certification. Tests throughout the construction phase of the development, conducted by a Passivhaus Certifier, ensure the targets laid out in the design process are met.
The results are impressive; Passivhaus-certified buildings use significantly less energy than conventional ones, achieving approximately a 70-80% reduction in heating bills, with options to go even further through Passivhaus Plus and Premium certifications, which incorporate renewable energy generation to offset consumption.
Evidently, this solves a crucial piece of the puzzle with regards to the carbon challenge associated with buildings, with the PHPP tool and certification focusing explicitly on operational energy reductions. And while this has driven tremendous reductions in the overall energy consumption of buildings here and abroad, several other critical aspects of a building’s carbon footprint are left unaddressed. In particular, the carbon emissions associated with the construction of the building and overall materials use, i.e. its embodied carbon.
Concrete Contradiction
Embodied carbon, which includes emissions from material extraction, production, transport, construction, and end-of-life processes, is becoming an increasingly more prevalent issue to tackle. With our overall energy grid decarbonising, our buildings becoming more energy efficient, and the move away from fossil fuels accelerating, the portion of a building’s total emissions made up of embodied carbon is growing.
For Passivhaus-certified buildings, this shift is particularly relevant. Materials like concrete, steel, and foam insulation, commonly used to meet Passivhaus airtightness and thermal requirements, can carry significant carbon footprints. This, therefore, creates a contradiction where operational efficiency is achieved at the expense of higher embodied emissions. Without addressing this issue, the long-term environmental benefits of operational efficiency risk being undermined by the upfront carbon costs of construction.
Addressing this trade-off calls for complementary strategies that focus on lifecycle emissions without compromising the benefits of Passivhaus.
As sustainability consultants, we advocate for a holistic design approach, combining Passivhaus assessments with whole-life carbon assessments (WLCAs). This would allow us to address not only operational carbon but also the embodied carbon associated with the materials. While we often navigate trade-offs between operational efficiency and embodied carbon, the latter is frequently overlooked. With limited certifications driving developers or landlords to prioritise embodied carbon, operational considerations tend to take precedence.
Rather than suggesting the PHPP tool is repurposed to include embodied carbon calculations, what if we expanded the Passivhaus framework to include an additional certification to the tiers that are dedicated to meeting low embodied carbon targets?
This certification would reward projects that demonstrate material efficiency, waste reduction, and responsible, local sourcing of materials. For example, buildings could achieve a ‘Low-Carbon Passivhaus’ certification by combining operational energy performance with an embodied carbon assessment or similar lifecycle analysis software.
A New Precedent
Any hypothetical Passivhaus standard could take a degree of inspiration from a new net-zero standard that has recently been introduced by a consortium of industry experts and respected bodies, including CIBSE, the Carbon Trust, and UKGBC. Known as the UK Net Zero Carbon Buildings Standard (UKNZCBS), this new framework introduces a series of benchmarks by which developments of different types must align themselves, in terms of carbon emissions from different sources, to ensure that they reach net zero.
Not only this, but the targets laid out in the framework are described as being ‘science-backed’. This means that they incorporate the latest climate modelling in order to create targets that would set the UK on a path to net zero, ultimately achieving a decarbonised housing sector and keeping the country on track to meet its obligations to limiting warming to 1.5°C.
It is in the greater focus of the UKNZCBS on embodied carbon where lessons could be learned for Passivhaus; split across several different factors – including operational energy, on-site renewables use, and upfront and lifecycle embodied carbon – the new standard provides guidelines on how to minimise emissions across the building’s lifecycle.
However, with this standard currently in its pilot testing phase, it will take some time to determine the effectiveness of such a standard.
What we could envision is a more joint approach that marries the best aspects of each standard. The new UKNZCBS, in taking a more holistic view of a building’s environmental footprint over the course of its lifecycle, allows for developers (and end users) to have greater assurance that their properties are sustainable. Despite this, the standard has been issued without any accompanying accreditation scheme that would allow organisations such as ourselves to certify that developers have achieved these standards, nor do they provide guidance on how to meet the standards (as Passivhaus do).
It is in providing this specific and actionable guidance that Passivhaus really comes into its own.