Understanding how buildings use energy is key to tackling the climate crisis, not only from an architect's point of view, but also from a building user's point of view. Sustainable architecture should fundamentally aim to be energy efficient to reduce our demand for natural resources, but when it comes to talking about building energy there is a lot of terminology and many buzzwords that get used.

Some of the terms that often get used in the context of sustainable architecture include ‘passive’, ‘net zero’ and ‘offsetting’. But what does each of these mean and what are the implications on building energy demand?

The context for this conversation is that we currently don’t have a realistic clean energy source that has no environmental ramifications. No matter how we produce and distribute energy it has some impact on the environment. In theory, the only way to produce a completely sustainable building would be to avoid the use of energy altogether. In practice however, this isn't realistic as human health and comfort is also a priority that needs to be considered in inhabited spaces. So we have to find ways to design that minimise our energy consumption, whilst maintaining internal comfort.

Passive Design

The first and most important design strategy for reducing energy consumption in a building is passive design. This refers to how the design uses the physical characteristics and physics of the building to move air and protect from the elements whilst creating a comfortable internal environment.

The shape of the building can be used to drive natural ventilation, shade from overheating and use physical mass to protect from outdoor temperatures. However, this has limitations when you bring into play weather extremes. High or low external temperatures, wind, rain etc will have an impact on what temperature the internal space reaches. This can also be affected by large numbers of people in a space, which can cause temperatures to rise and also contributes to higher levels of CO2, which makes a space feel stuffy and can cause drowsiness.

So passive design can work in certain circumstances, and should be used where possible, but it doesn’t work for all building types and uses. This is when mechanical systems are introduced to drive ventilation, provide heating and achieve good light levels.

Low energy design

The vast majority of buildings use energy for heating, cooling, lighting and ventilation, which consume enormous amounts of energy globally. By designing to passive principles we can reduce the energy demand of the building but it is also possible to design for low energy mechanical systems.

Passivhaus is a design standard that aims to minimise energy consumption of a building by highly insulating and providing good air tightness, but crucially, these systems are supplemented with energy efficient mechanical systems that maintain internal comfort. The ‘MVHR’ (mechanical ventilation with heat recovery) draws stale air out of the building, and extracts the heat from this to warm up fresh air coming in. This means that wasted heat from our bodies, computers and kitchens gets reused to heat the building.

By thinking resourcefully about space and energy we can reduce the energy intensiveness of our buildings and further reduce our demand for natural resources.

Net Zero Energy Building

Ideally, a sustainable project will have implemented as many energy efficient design considerations as possible from the outset, but there will likely still be a remaining demand for energy in the building.

Net Zero Energy describes the idea that the total amount of energy consumed in the building can be matched by energy generated on site. This could include energy generators like solar panels, wind turbines, or ground source heat pumps. You therefore end up with a ‘net zero’ expense on energy as all the energy you need is created by the building.

Net Zero Carbon design

‘Net Zero’ often gets mentioned in isolation, but it’s important to understand the difference between ‘net zero energy’ and ‘net zero Carbon’ design approaches. In principle, these both relate to the idea that the amount of energy or carbon required in a building is balanced out by applying additional measures that balance the scales.

In the construction of buildings, carbon is emitted as part of the construction process (embodied carbon) and in the operation of the building (operational carbon). To reduce this impact, designers can consider measures to reduce the amount of carbon emitted.

Operational carbon is directly related to the energy efficiency of the building as it is largely a result of the amount of energy used in heating, lighting, ventilating and powering the spaces. To reduce these, passive design strategies and on site energy can greatly reduce the operational carbon emissions.

Embodied carbon is more tricky and is connected to the types of materials and construction methods used. The best way to reduce embodied carbon is to source materials that are least energy intensive to extract and manufacture, or that sequester carbon. Sequestering refers to the process of absorbing and ‘locking in’ carbon, specifically in wood, which absorbs carbon during the time that it grows. This is then contained in the physical material of the timber, which can be stored in the fabric of a building. The overall effect is that more carbon is locked into the fabric of the building itself, than was emitted as part of the construction process.


Net zero Carbon buildings are achieved by balancing out the amount of carbon emitted in the construction process. This process of balancing is commonly known as ‘offsetting’. In addition to the example mentioned above, using timber to offset carbon, offsetting could be achieved by including on site energy strategies, or by contributing to planting trees which absorb more CO2 during their life cycle.

Offsetting a term that is often advertised by companies or projects as a sustainability credential, to advertise ‘greenness', and whilst it is a good measure to balance out an otherwise sustainable design, it is not best practice by itself. The best approach is not to offset at all, but aim to reduce emissions from the outset of a project. It’s important to highlight that large scale extraction of fossil fuels can’t be undone, regardless of what offsetting measures are used.

Offsetting measures such as planting trees, whilst great for biodiversity and CO2 absorption, will not have a meaningful effect on carbon emissions in the short term. If we are attempting to offset large amounts of energy spent as a result of inefficient building design, we are applying a band aid solution to a deeper problem.

Terms such as ‘offsetting’ are often presented as a complete approach to sustainability, but do not address the more fundamental work that needs to be done to meaningfully impact climate change. Reducing building energy use and carbon emissions are central to creating sustainable architecture and it is essential to make sure that terminology of this topic is well understood to help us evaluate sustainability claims when they are made.

- Maria Henshall

What is embodied carbon?

Embodied carbon is the total carbon emissions as a result of the construction of a building, including in the mining, transportation and processing of the building materials, the assembly of the building and on-site construction activities.

Why is it relevant in my article series?

In these articles, I am exploring how architects can contribute to the response to the climate crisis. Carbon emissions are a global challenge and understanding the embodied carbon of buildings is a significant part of the overall picture.

How relevant is it in architecture in general?

A building’s overall embodied carbon is impacted by the choice of materials and processes used in its construction.

Architects are fundamental in making these choices as part of the design process, and having a knowledge of embodied carbon is important for moving towards more sustainable buildings.

What could be done to reduce embodied carbon?

The manufacture of materials such as steel, concrete, aluminum, and glass for use in building construction contribute significantly to global carbon dioxide emissions. By selecting construction materials that require less energy-intensive manufacturing process, or raw materials that require less intensive mining processes we can reduce the embodied carbon of a building. Transport distances can also have an impact on the embodied carbon of a material when considering where materials need to be sourced from.

What can you do?

Engage with activism and petitions that challenge the current industry, for example ACAN, is campaigning to introduce embodied carbon legislation in the U.K. that would allow the planning process and building regulations to assess, report and reduce embodied carbon emissions of construction projects.

This legislation would bring a much higher level of environmental accountability to projects, which is currently too easily ignored.

- Maria Henshall


In the brief for these articles, one of the things Sannah challenged me to think about was how people could take action in their personal lives to tackle the climate emergency, through the lens of architecture. What is interesting is I have spent a lot of time with colleagues and tutors considering how architects can operate more sustainably, but I have really no idea how someone outside of the industry could also engage and have an impact.

Although architecture is something that everyone experiences in their day-to-day life, the process of producing architecture is largely shielded from the public eye. Entry to the industry is gated by many levels of education and professional qualifications. These can take the best part of a decade to obtain, before you can even start thinking about what your contribution to the industry might be. The result of this is that, other than possibly some community engagement sessions that might happen for urban projects, there is really no way for the public to contribute directly to or critique how architecture is produced.

In my view, there are a few key ways that it is possible to make an impact on the built environment, even if you are not directly working in the field as a professional.

Firstly, many people are opting to be self-builders, which essentially refers to the process of acquiring land and building a new-build home. Anyone looking to build their own home has a fantastic opportunity to create a sustainable, regenerative space that uses low impact materials, high thermal efficiency, passive design or efficient mechanical ventilation systems, and off-grid energy possibilities.

Building standards such as Passivhaus are brilliant, as it acts as a guarantee for the homeowner that the house will perform as promised (the key with Passivhaus is that the building needs to pass an inspection after completion). Unfortunately, self-build is an option open to very few - those with the time, money and willpower to see through several years of chaos. Not to mention the process of finding a plot, which in the U.K. is a project in itself. For many, renovation, home upgrades, and interior design are the most effective way to directly influence the environmental impact of their inhabited environment.

Homeowners (and in some cases renters) can consider retrofit upgrades that could reduce the energy demand of the house such as adding insulation, upgrading to double or triple glazing, swapping to low energy appliances and lightbulbs. In addition to this, smart tech is a fascinating growing industry which enables features such as smart metering and automation of lighting, heating and other electronic fixtures. Learning to use smart tech effectively will inevitably empower us to understand and monitor the energy consumed in the spaces we inhabit.

Finally, the most effective way that anyone can make a direct impact on the built environment is through activism and backing legislation or policy change. System change and government scale investment in subsidies are some of the most effective ways to shift trends to a more resilient future.

A fantastic example of a campaign in the U.K., which is being run by ACAN (Architects Climate Action Network), is seeking to introduce embodied carbon legislation in the U.K. that would allow the planning process and building regulations to assess, report and reduce embodied carbon emissions of construction projects. Embodied carbon is the total carbon emissions as a result of the construction of a building, including in the mining, transportation and processing of the building materials, the assembly of the building and on-site construction activities. Although embodied carbon calculations can be complex, this legislation would bring a much higher level of environmental accountability to projects, which is currently too easily ignored.

Another example of an ongoing campaign is ‘RetroFirst’. This campaign is looking to achieve VAT cuts for retrofit projects that improve the energy efficiency of a building. Currently, the VAT system is biased towards new builds, which do not incur the tax. Under the proposed changes, new builds would be subject to the full VAT rate, unless the building can be shown to meet a rigorous energy efficiency standard. It’s essential to look to improve the existing building we have first, before incentivising new construction, which ultimately depletes our raw materials and natural resources, and increases the amount of embodied carbon in our building stock.

Much of this change will need to happen within the industry, with sustainable agendas being driven by built environment professionals who are familiar with the challenges at hand. However, involvement and engagement by non-architects will also be crucial in developing a wider culture that views the environmental impact of buildings and cities as urgent and fundamental in achieving a more sustainable future.

- Maria Henshall