Net zero buildings: the future of construction?

A growing number of buildings are being touted as ‘net zero’. We ask what this really means and how realistic it is to make buildings carbon neutral.

With humanity scrambling to respond to climate change, countless companies, investors, public sector bodies and national governments have made commitments to achieve ‘net zero’ carbon emissions in the next two or three decades.

Net zero is the notion that any greenhouse gases (GHG) emitted through an organisation’s activities must be balanced out through an equivalent amount of carbon being removed from the atmosphere. It is a huge challenge, yet if we are to avoid the worst effects of climate change, achieving net zero will be vital.

There is one industry where meeting such targets is especially important: construction. Globally, some 39 per cent of GHG emissions are associated with the industry, according to the World Green Buildings Council. Of this total, 28 per cent comes from operational use – heating, cooling, and lighting – while the remaining 11 per cent are ‘embodied emissions’ (the materials and building process).

To make construction ‘net zero’ would require an enormous shift in how the entire industry works. Yet, as Patrick O’Flynn, a built environment lecturer at the University of the West of England points out, “the construction industry is a relatively conservative industry; we’re relatively slow moving compared to other disciplines”.

Nevertheless, there is a lot of work going into making construction more environmentally friendly.

As the seven examples listed below demonstrate, there is a growing number of construction businesses, architects and developers producing buildings that aim to be net zero.

The idea of a net zero building appears relatively simple at first. It would be a structure that generates as few emissions as possible during construction and operation. Where GHGs are released, the developer – or eventual owner – would offset them. Yet scratch below the surface and defining what ‘net zero buildings’ are, and what makes something carbon neutral, becomes very complicated.

“I give an analogy that net zero buildings are a bit like fitness” explains O’Flynn, in that “there’s no one definition of fitness, but you know it when you see it”. A 100-metre sprinter has a very different kind of fitness to a marathon runner, who in turn has a different kind of fitness to a tennis player.

In the same way, different kinds of net zero buildings will have very different features depending on their purpose, but they are all highly performant when it comes to energy usage. A net zero residential flat might achieve this ‘fitness’ by being extremely well insulated, whereas a big office park might achieve net zero by packing the roofs with solar panels to generate energy onsite.

There is no single model for building something in a ‘net zero’ way, and this makes it difficult for architects and construction firms to know exactly how to proceed.

The second complication is the way a building’s carbon emissions can be divided into two parts. As noted above, there are embodied emissions (those associated with production of bricks and mortar, transport to site, energy used to dig foundations and put the structure up). Then there are the operational carbon emissions. This is all energy used throughout the building’s lifespan to keep it heated, cooled, and lit up. Calculating true carbon emissions of both these ‘costs’ is extremely complex.

Right now, it is (comparatively) easier to figure out the operational carbon costs. In the UK, as in many other countries, all buildings come with an Energy Performance Certificate (EPC), which designers are obliged to produce to show how efficient they are in terms of energy usage.

To calculate energy performance, O’Flynn says architects use various thermal equations. The trouble is that this energy rating is based on what a ‘standard’ user’s energy consumption would be like.

However, of course, there’s no such thing as a standard person, and so some people could use far more energy than predicted on the EPC.

Then there is the issue of calculating embodied carbon in a building. This refers to all emissions associated with extraction, manufacturing, and shipping of materials to a building site. At present, there’s no obligation to calculate these emissions, and trying to tot them up is very hard due to the global nature of supply chains.

Despite these difficulties, there are efforts within the industry to try and make ‘net zero’ construction more tangible, feasible and practical for all kinds of builders.

Tom Wigg, an advisor at industry body UK Green Building Council (UKGBC), says his organisation has worked with numerous expert bodies to collaborate on the UK’s first net zero carbon building standard, which should hopefully be launched in 2023 (the other partners are: BBP, BRE, the Carbon Trust, CIBSE, IStructE, LETI, RIBA and RICS).

Wigg explains that a lot of conceptual work has been going on for several years by various institutes and researchers. The aim of the new standard “isn’t to reinvent the wheel”, but to draw together lots of existing measures and guidance into one coherent framework. Any builder can use it to verify their plans are net zero, and prove they are to customers. This will, hopefully, make ‘greenwashing’ harder.

At the operational stage, this new standard will go much further than today’s EPCs. The standard will use stringent methods for calculating carbon emissions at initial design, then again at the practical completion stage, and another measurement of emissions once the building is in use. This means a building’s true energy emissions are measured – not just the estimates of the EPC.

The standard will also focus on the embodied carbon in buildings. Wigg explains a growing number of construction materials today come with an EPD (environmental product declaration). This quantifies greenhouse gas emissions associated with their production (although EPD’s are not available for most products yet).

The hope is that “the materials you’ve specified will come with a robust EPD, that specifically relates to that material or product that’s arrived on site, and you’ll know the exact emissions of that particular product”. This, however, remains more of an aspiration than a reality; most building materials do not come with this data. Nonetheless, there are tools for estimating these figures.

Hopefully, calculating embodied and operational emissions will become easier in future using software. O’Flynn says Building Information Modelling (BIM) technology – which helps architects draw interactive digital blueprints – could include these calculations as a designer is drawing out a building’s plans. The software could feasibly show them how much emissions are generated with different designs and materials and help them more easily create environmentally friendly structures.

“The technology is there” to make net zero buildings a reality, reckons O’Flynn. “We know how to do passive houses [very well insulated buildings that need little external energy input], we know how to do the technology in terms of things like heat pumps”. The real barriers, therefore, are economic and social.

Part of the issue is what end customers want. “There isn’t a builder or an architect in the country who will give a client what they don’t want,” O’Flynn remarks. So, if customers aren’t convinced of the need for a net zero building, architects and builders are unlikely to force one on them.

From an economic perspective, net zero designs are generally seen as more expensive to build. As a very rough rule of thumb, it’s believed they cost about 25 per cent more to build than standard designs.

However, he points out that this isn’t always the case. For example, Goldsmith Street, a council housing development of passive homes in Norwich (more below), which won the 2019 Stirling Prize for Britain’s Best New Building, only came in at 14 per cent more expensive than regular methods.

With economies of scale, O’Flynn reckons costs of net zero buildings could reach parity with traditional methods. The other advantage is that residents’ energy bills should be lower.

A different challenge comes from the energy industry. O’Flynn reports that most of the country’s big energy firms have professional lobbying outfits who are very active in Westminster. Naturally enough, these firms are opposed to any rules and regulations that mean less energy gets used in homes, offices, and factories.

O’Flynn also points out that net zero buildings need to be built at scale if they are to have any serious impact. At present, many net zero buildings are very much one-offs, but this way of building needs to be used on a big scale if it’s to shift the needle.

Despite these barriers, momentum does seem to be with those pushing for net zero buildings. Tom Wigg of UKGBC says that when he started his career at a sustainability consultancy, “we were the bad guys in the room”, and builders were looking to do the bare minimum. However, almost all UK local authorities have now declared a ‘climate emergency’. He says that today, “the vast majority of large investors and developers have corporate net zero commitments”, and this is gradually feeding into actual projects.

While we’re a long way from eliminating carbon emissions from the built environment, it does seem like the industry is moving in the right direction. However, Wigg cautions against getting carried away – and points out the elephant in the room. “We have 30 million homes in the UK that need to reduce their energy demand, on average, by around about 60 per cent,” to get the country on course for net zero. As positive as it is that new buildings are being designed in an eco-friendlier manner, the true challenge will be to insulate our existing building stock. And that will require a much bigger effort.

Seven kinds of net zero buildings

What does a net zero building look like? Here are examples of net zero structures from around the world.

Residential: Goldsmith Street, Norwich (UK)

Winner of the 2019 Stirling Prize, Goldsmith Street is a social housing development built to Passivhaus standards (essentially, well-insulated buildings which can mainly be warmed by the sun, human occupants and household appliances, with almost no active external input).

The 93 terraced houses come with several smart features to reduce energy usage, including window placement, sloped roofs to maximise daylight, letterboxes in external porches rather than front doors to reduce draughts, and a solar energy scheme to further reduce carbon emissions.

Are net zero buildings the future of construction?

Image credit: Marcel Ilzerman

Offices: Floating Office Rotterdam (the Netherlands)

As the name suggests, Floating Office Rotterdam (FOR) is a three-storey office building which bobs away in the port of Rotterdam. Made largely from timber (which is, arguably, a sustainable material if new trees are grown), the modular building sits on a floating platform that rises and falls with the tides. Its designers note that this protects it against flooding from sea level rises too.

FOR claims the office is carbon negative and energy positive (it exports energy to the grid thanks to solar panels on its roof). Since the building can be taken apart and its constituent parts reused, it also ties in with the notion of a ‘circular economy’ – less waste at the end of the building’s initial life. In addition, it has a green roof packed with plants to encourage biodiversity.

Being built on the river allows FOR to use the surrounding water as a heat exchange. In summer, the river water is colder than the air above, which helps keep the place cooler. In winter, the opposite is true, with the warmer river water helping heat the building up.  

Warehouse: Apex Park, Daventry (UK)

As e-commerce grows, UK warehouse construction has boomed – often with minimal environmental benefits. Yet this 435,000 square foot warehouse, which opened last year as the UK logistics centre for US multinational Cummins, has gone beyond net-zero carbon in its construction and operation, according to developer Prologis.

Sustainability features include rainwater harvesting, EV chargepoints and a 1.4MW rooftop solar array. With a Cummins gas generator set in a standby application, the building should generate more energy than it uses and can feed electricity back to the grid.

Hospital: The Balfour, Orkney (UK)

The new £64m NHS Orkney hospital is the healthcare hub for the islands’s 22,000 residents. As Robertson, the lead contractor, explains, the 49-bed health centre has been designed to be carbon neutral.

In terms of its operational carbon, the building incorporates passive design to minimise energy usage. It is entirely powered by electricity (there is no gas on Orkney), with most coming from electric heat pumps, and hot water from air to water heat pumps. The lights are also kept on by a 1,200m2 rooftop solar array.

When it comes to embodied carbon, efforts were also made to minimise impact. The contractor notes that some 98 per cent of timber used in the hospital was from certified and reused sources, and 100 per cent of waste was diverted from landfill.

School: Sweyne Park, Essex (UK)

Morgan Sindall Construction led the way on the construction of a new teaching block at Sweyne Park School in Rayleigh (including classrooms, WCs and staff rooms), as well as two other schools in the English county.

The project used prefabricated modular units, manufactured by Eco Modular Buildings and then installed onsite, and the building incorporates several net-zero features. These include solar panels, air-source heat pumps and low-energy ventilation, as well as plenty of insulation. This makes the Sweyne Park building ‘net zero’ in operation, one of the first school buildings in the country to achieve this.  

University: School of Design & Environment, National University of Singapore (Singapore)

How do you keep a large building with multiple occupants cool in a humid tropical climate, without relying on energy-hungry air-conditioning systems? Architecture firm Serie used several net-zero design elements to address this issue at a new campus building at Singapore’s national university.

The 8,500m2, six-storey building includes several features intended to minimise energy use. A rooftop solar array is used to power an air-conditioning system that distributes tempered air to rooms, and this is then distributed via fans. The method is much less energy intensive then traditional AC systems.

Government: California Air Resource Board (USA)

CARB is a US government facility that measures and analyses vehicle emissions, so it is fitting that a building which tests carbon emissions from cars should be carbon neutral itself.

Features designed to achieve net-zero emissions include 10,000 photovoltaic panels on the roof (meaning all energy requirements are met onsite), bike lockers and 120 charging stations for EVs.

Clever placing of windows means much of the laboratory’s lighting comes free from daylight, and insulated windows keep interiors cool against the California sun. Finally, native trees have been planted around the campus to absorb CO2. 

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