What is ‘net zero’?
According to utility provider National Grid (NG), which owns the high-voltage electricity transmission network in England and Wales, “net zero” means “achieving a balance between the greenhouse gases put into the atmosphere and those taken out.”
NG uses the analogy of a bath: “Turn on the taps and you add more water; pull out the plug and water flows out. The amount of water in the bath depends on both the input from the taps and the output via the plughole. To keep the amount of water in the bath at the same level, you need to make sure that the input and output are balanced.”
Reaching “net zero” applies the same principle, according to NG. It requires us to “balance the amount of greenhouse gases we emit with the amount we remove. When what we add is no more than what we take away, we reach ‘net zero.’”
Why is net zero necessary in construction?
The need to stem rising temperatures—largely through ending our reliance on fossil fuels, which emit millions of tonnes of environment-damaging carbon into the atmosphere—is familiar to most.
Becoming more sustainable in terms of the energy we use in our homes is now an accepted fact of life. Most acknowledge the need to look at alternatives to coal, oil and gas such as solar power, wind turbines and heat pumps.
For good reason. Experts say society should be aiming for a net zero situation, particularly across construction, and that includes net zero home building. But what does this look like in practice? And how can householders—and those building the homes of the future—play a part in turning the tide of climate change?
How can we achieve net zero homes?
In line with NG’s definition, a net zero or zero emission house is one that is energy efficient to the point that its energy needs are matched by the renewable energy it takes to match that need.
Renewable energy and efficiencies come in the form of solar power, good water management, good thermal and ventilation performance, and efficient lighting.
Transforming existing housing stock into net zero homes
New homes are increasingly designed to be energy efficient. According to the Cambridge Centre for Planning and Housing Research (CCPHR), “net zero carbon-ready homes are those that are built with high energy efficiency and use low carbon technologies (such as heat pumps or other forms of electric heating, instead of gas boilers) that will become net zero carbon when the national electricity grid is decarbonised.”
The CCPHR says that such homes “will not need retrofitting in the future in order to have net zero carbon emissions from their regulated operational energy.”
The retrofitting point is pertinent. Delivering new housing stock by using modern techniques and technologies from the outset is relatively straightforward. Making homes that have been around for decades—or even hundreds of years—energy efficient , let alone net zero, will be a considerable task.
“The average household energy performance certificate (EPC) rating in across UK homes is D (ratings range from a high of A to a low of G),” says Insight Investment.
“UK housing emits almost 100 million tonnes of CO2 each year, accounting for 27.9% of the UK’s total of 326.1 million tonnes of CO2 emissions in 2020. The UK government aims to reduce CO2 emissions in 2035 by 78% from 1990 levels, meaning the UK would need to emit a total of only 140.1 million tonnes of CO2 emissions.”
To hit these government targets, the average UK household would need to have a minimum EPC rating of C; the cost of upgrading the country’s homes to this level would be £94 billion, according to Insight Investment. Others suggest the figure could be as high as £200 billion.
Measuring the costs of net zero home building
While there will be upfront costs involved in addressing climate-related issues, the advantages of building net zero homes are clear. So are there any downsides? There are not regarding day-to-day operation.
But delivering net zero homes that have a drastically reduced embodied carbon element—where the carbon is in the materials used to build them—is trickier to achieve.
The structure of a home holds most of its embodied carbon, said Aecom systems engineer Rob Mills. “For a medium-sized residential building, the London Energy Transformation Initiative (LETI) says 46% of embodied carbon is in the superstructure, 21% in the substructure, 16% in internal finishes, 13% in the facade and just 4% in mechanical, electrical and plumbing engineering.”
The primary focus must therefore be on reducing emissions from structural components, according to Mills. Greener cement, greater use of timber—a good repository for carbon—and so on.
The cost of building net zero homes or other structures is high because the technologies used aren’t common. Some suggest it could be as much as £40,000 on top of the average build cost. But as more projects and developments are delivered, and the know-how to get the technology right increases, these expenses will start to fall.
Is carbon offsetting a solution?
Examples of net zero homes in the UK are rare. One example is the London residence of the late Max Fordham, a celebrated architect, which was verified net zero carbon as per the UK Green Building Council’s Net Zero Carbon Building Framework.
The home is mainly a new build, with some elements of existing structures repurposed. Carbon emissions during its construction were minimised by using concrete with low-carbon cement replacement, while timber was used for the roof structure, window frames and façade. Insulation came via use of woodfibre, cork flooring and triple-glazed windows.
Embodied carbon during the Fordham house’s construction was offset. Offsetting happens when organisations buy carbon credits generated by projects that are cleaning up the atmosphere to compensate for their emissions.
According to management consultancy Deloitte, the quality of some carbon offsetting projects is open to question, “but when done well, they support local economies and fund work that is making a real impact.”
Conversely, environmental activists take a dim view of offsetting. Greenpeace said that “for corporations, carbon credits cost them a pitiful amount of money whilst they can continue their emission-intensive business as usual, and still market themselves as a ‘climate champion.’”
“This is not only bad for our climate,” Greenpeace said, “it’s unjust, as it often puts a massive burden on those marginalised communities most affected by the climate crisis.”
Overcoming the challenges of net zero construction
Perhaps the last word on net zero homes, for now at least, should go to Terrie Alafat, chair of the Building Back Britain Commission (BBC), created in 2021 to push the housing agenda in the UK.
“With around one-in-five of the homes that will exist in 2050 yet to be built, we must simultaneously do everything possible to ensure that all new developments have the highest possible levels of emissions reductions,” Alafat writes in the ”Building Back Britain: Net zero and the housing challenge” report, published in May 2022.
“New build developers are already leading the way here with significant steps forward in recent years. The average new build home now emits at least two tonnes less carbon each year than the average existing home, and consumers are feeling the benefits with significantly lower energy bills.”
Alafat and her BBC colleagues acknowledge that there will be challenges, but adds that, in the long term, “taking radical action now to make our homes more energy efficient will enable the UK to make much-needed strides forward on the path toward net zero.”
“In the short-term, it will also mean lower fuel bills for millions of people who are suffering as a result of the energy crisis and urgently need help with the cost of living.”