10 Net Zero Carbon Myths

To be Net Zero Carbon a building must be verified as NZC each year depending on the measured energy use at the building’s energy meters.

It is possible to design and construct an ultra-low energy or a “net zero carbon compatible” building. There are also tools available (such as Passivhaus) which have been shown to help ensure that in-use performance is as close as possible to that designed. However, it is the case that most buildings will not be able to meet all their energy requirements on site and will still draw a residual amount of energy from the national grid. To be verified as net zero carbon these remaining operational carbon emissions will require to be offset offsite through a verifiable carbon offsetting scheme.

PV use is an essential part of the national net zero strategy, so we certainly encourage their installation. However, it is important for all of us to see the whole picture and consider the climate impact of our decisions, such as the “embodied carbon” emissions arising during the manufacture of PV panels and any other systems.

A 1kW (around 7m²) PV array in the UK can generate around 900 kWh of electricity, depending on its location. The same PV panels in use generate zero carbon electricity and displace (or save) around 180 kgCO₂ of emissions which would have arisen from the national electricity grid. The reported embodied carbon of a 1kW PV array can vary widely, however it is typically in the range of between 1,000-2,000kgCO₂, and so it takes around 6-12 years for the PV panels to offset the carbon emissions arising from their own manufacture before they start reducing the lifetime emissions of a building.

Not necessarily! For many years the Greater London Authority’s (GLA) definition of net zero carbon only considered the operational energy of “regulated” building systems (fans, heating, lighting etc) and was based on compliance modelling which is known to generally be a poor indication of in-use performance. It is therefore likely that buildings designed to just meet the requirements of the London Plan are in fact a long way off being net zero carbon.

In its most recent draft update issued in 2019, the GLA is seeking to address some of the gaps and has started to ask major developments to report at planning on lifecycle carbon emissions and to commit to achieving low energy use in operation through its “be seen” policy.

The embodied carbon data for building materials and components is currently limited and in some cases absent meaning that proxy products must be used in lifecycle assessment which might be a poor representation of reality. The data that does exist also has a relatively high degree of uncertainty. The analyses of material and component life cycle carbon emissions typically assume constant technologies and electricity grid carbon factors for the full life duration (e.g. 120 years). The future is uncertain, but change is likely, therefore the assessment of future carbon emissions is likely to be inaccurate.

The predictions for embodied carbon for the production and construction lifecycle stages of a building’s life (RICS stages A1-A5) have a much higher degree of certainty than the maintenance, replacement and end of life stages (RICS Stages B1-C4). As such we think it is of most benefit to consider the production and construction stages of the lifecycle analysis to influence design decisions, rather than the full lifecycle (A1-C4). This also aligns with the need to cut carbon emissions drastically in the near term.

Not true, although complicated by constraints such as building age, construction type, condition, occupants and available budget, significant improvements in performance can be made through a planned retrofit, which can of course be staged over time. Minimising energy demands through improvements to the building’s thermal insulation, glazing, air tightness and ventilation systems should be early steps, but significant reductions can also be achieved through relatively simple measures such as installing and maintaining efficient lighting and controls, efficient M&E plant and selecting equipment such as IT systems specifically for low energy consumption. Occupant behaviour and education also contributes significantly to in-use energy consumption.

It therefore seems reasonable to firstly put a plan in place to improve one’s own existing building, to move away from burning gas for heat and to combine these steps with a short-term strategy of verified carbon offsetting. This would allow many existing buildings to become net zero carbon.

Firstly, well done for signing up to a renewable or green energy tariff, this is in many ways the simplest step an individual or organisation can take to show that they care about where their energy comes from. However, it is worth finding out more about your energy supplier’s “renewable energy” tariff.

For every 1,000 kWh of electricity that a renewable generator produces, the regulator OFGEM provides 1 Renewable Energy Guarantee of Origin certificate (REGO). Both the electrical energy and the REGO certificates can be traded independently. REGO certificates can typically be bought very cheaply for around 35p each, so are considerably cheaper than the cost of the renewable electricity itself.

It is possible for an energy supplier (who for example only operate natural gas fuelled power stations themselves) to market a renewable energy tariff product backed up by traded REGO certificates. Buying your energy from these companies doesn’t necessarily result in an increase in the supply of renewable energy. There are however energy suppliers who only sell renewable energy that they produce or that they have agreements in place with generators to purchase. Researching and purchasing energy from these companies can contribute to the funding of increased renewable energy generation.

Due to the uncertainty over origin of the energy supplied, the UKGBC’s definition of a net zero carbon building does not consider the effect of a green energy tariff.

Current regulations assign a low CO₂ emission rate to the burning of biomass, therefore the use of biomass to heat our buildings appears to be a positive climate choice. However, In the short-term burning biomass results in a rapid release of CO₂ and other combustion by products such as NOx and particulate emissions, which contribute to climate change and local air pollution. The world needs to end carbon emissions and start work to reduce atmospheric CO₂ levels as soon as possible, by 2030 if we are to avoid the worst effects of climate change. Burning biomass might be carbon neutral over a certain time period, e.g. 100 years, but it is unlikely to be climate change neutral without significant advances in carbon capture and storage technology.

It seems likely that in the near future planting more forest and using well managed forests for long-lived timber products and building materials is a better approach to the use of biomass to mitigate climate change.

Any steps which can be taken to reduce or stop burning natural gas should be prioritised. Hydrogen can be produced from excess renewable energy generation (“green hydrogen”) or from reformation of natural gas (“blue hydrogen”). Without use of the enabling technology known as carbon capture and storage (CCS), blue hydrogen results in the release of the same carbon dioxide emissions as would otherwise occur using natural gas. The National Grid’s future energy scenario planning predicts large scale industrial pilot projects utilising hydrogen and CCS will start to appear in the 2030’s, with wider availability of hydrogen possibly appearing in the 2040’s. This is a long way off in relation to the climate emergency and the future is uncertain. To reduce carbon emissions now and in the coming decades, new heating systems should seek to utilise low carbon sources of heat such as electric heat pumps.

That really depends on where it comes from. If the heat is generated from burning gas, it is very far from low carbon. If it is from an electric heat pump, it can be better. Burning waste releases more carbon into the atmosphere than anything else. Accurate assessment of heat losses from the distribution pipe network and energy consumption of pumps and controls have to be accounted for in the overall assessment of the carbon benefit of a district heating system.

Does your project manager understand how net zero ranks amongst your other priorities, and do they understand what they will need from each design discipline? Does your cost consultant have access to relevant data to give you the cost certainty you need?

To make it happen, every member of the design team needs to be on board, be able to understand the objective and be capable of adapting their approach. A design team will make tens of thousands of decisions in the design of a building. All these decisions will influence the building's climate impact. Make sure you hire the right team and have a robust strategy to keep them on track and working together.