27 March 2024
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Net zero and greenhouse gas emissions

What do we mean by net zero?

It is essential to understand that while human activity contributes to increased greenhouse gas emissions, the Earth requires a certain level of naturally occurring greenhouse gases to keep the planet liveable. Therefore, our primary goal of net zero is to reduce the built environment’s negative impact and take actions that support the necessary balance required for continued life.

The term ‘net zero’ comes from the 2015 Paris Agreement, which the United Nations defines as ‘cutting all greenhouse emissions to as close to zero as possible, with any remaining emissions re-absorbed from the atmosphere’.

Put simply, net zero creates a balance between the amount of greenhouse gases produced and the amount removed to achieve an overall near-to-zero result. Therefore, our efforts to reach net zero should be twofold: 1) reduce the amount of greenhouse gas that we produce, and 2) remove as much of what we do produce to achieve a result near net zero.

Greenhouse gases and how the human world impacts their production

While carbon dioxide is the most prevalent greenhouse gas released by human activity, the Paris Agreement addresses seven gases that fall under the term ‘greenhouse gases’ and have global warming implications.

  • Carbon dioxide (CO2) is naturally produced by living organisms (humans, animals, plants, etc.) during respiration and through decaying biomass. It is unnaturally produced via the burning of fossil fuels and chemical reactions. Buildings are responsible for approximately 39–42% of worldwide global emissions. In the next section, we discuss the various ways they contribute.

    Naturally, CO2 is removed through photosynthesis, where plants convert carbon dioxide into sugar and oxygen; any held CO2 is only released when the plant dies. Forests, in particular, play an essential role, as trees have natural lifespans ranging from as much as 200 to over 1000 years.

  • Methane is a colourless gas created by producing and transporting oil, natural gas, and coal and agricultural practices like fishing, forestry, and livestock raising. Landfills are one of the largest sources of human-generated methane emissions, with methane and carbon dioxide making up 90–98% of landfill gases.
  • Nitrous oxide is created from agricultural and industrial activities such as fertilizer use, timber burning, fossil fuel and solid waste combustion, wastewater treatment, and other land use activities.
  • Hydrofluorocarbons have numerous uses, including propellants for aerosol and asthma sprays, blowing agents for fire extinguishers and foams, and heat absorbents in air conditioners, heat pumps and refrigerators/ freezers. According to a European Parliament publication on climate change and greenhouse gases, hydrofluorocarbons represent approximately 90% of fluorinated gas emissions. They currently have numerous uses, which the EU hopes to phase out by 2050.
  • Perfluorocarbons are manufactured compounds used in industrial manufacturing.
  • Sulfur hexafluoride is used extensively as an insulator in high-voltage electrical switchgear.
  • Nitrogen trifluoride is used to clean excess build-up on microprocessors and circuit parts during production. 
  • Water vapour is another significant greenhouse gas, accounting for almost half of the greenhouse effect. However, water vapour neither causes global warming nor directly increases its concentration. Instead, it serves as an amplifier for other greenhouse gases, thus increasing their impact on global warming.

The built environment and carbon production: operational, embodied and whole life

In the built environment, we focus on two primary sources of greenhouse gases: operational carbon and embodied carbon. The sum of these two things determines a building’s whole-life carbon footprint.

  • Operational carbon is the energy that a building or process uses during operation.
  • Embodied carbon is the amount of carbon generated from the products and processes used to create and maintain a building. This includes raw material extraction and refinement, manufacturing processes, packaging, transport installation, maintenance, and end-of-life activities like disposal and recycling.

 The reduction of carbon emissions can be achieved by:

  • Reducing the amount and type of energy used.
  • Using required energy more efficiently.

To that end, an industry-proposed ‘Document Z’ is being developed. If approved, it should help designers and specifiers better address embodied carbon by emphasizing comprehensive whole-life carbon assessments, which will aid in better capturing and reducing embodied carbon numbers. The proposed document aligns with the RICS professional whole-life carbon statement and recommendations and guidance from industry leaders, including the RIBA, IStructE, CIBSE, UKGBC, and LETI. The dedicated Part Z UK web page provides more information on the proposal and a link to download a copy.

UK legislation

As amended, the Climate Change Act 2008 is the critical piece of legislation for net zero. As a result of the Act, the Government set up the Climate Change Committee, which sets carbon budgets every five years. Subsequently, significant decreases in UK carbon emissions have been recorded. The UK has committed to achieving net zero by 2050, and it is expected that the Climate Change Committee’s subsequent carbon budgets will become more ambitious to meet the 2050 deadline. The UK is the first country to set legally binding carbon budgets that restrict the amount of greenhouse gases emitted over five years.

Building Regulations guidance documents set out what is acceptable when complying with the regulations. However, those designing or undertaking building work are responsible for assessing whether specific circumstances require additional or alternative approaches to achieve compliance.

Energy efficiency

Ventilation

Overheating

NBS Chorus guidance provides further detail regarding regulations as they apply to each country

Energy efficiency, ventilation and overheating: connected design for optimal results

A multidisciplinary approach should be used to consider how ventilation, energy efficiency and overheating work together from the early design stages. By carefully considering all three factors, optimum efficiency can be achieved while reaching desired indoor conditions for thermal comfort and air quality.

As a set, England’s Approved Documents L, F, and O – or their counterparts as set out above – provide essential guidance on the critical interactions between overheating, ventilation and energy efficiency.

Approved Document L: energy efficiency (conservation and generation)

The two volumes comprising Approved Document L provide guidance for energy efficiency. Both deal primarily with common building situations. Therefore, it is essential to remember that complying with the guidance may not guarantee compliance with the regulations when dealing with variations, innovations and other less common circumstances. Designers and specifiers may need to consider different approaches to sustainability and general energy efficiency to ensure that the building meets regulations.

The 2021 edition of Approved Document L has more stringent requirements than previous publications. Subsequent revisions (expected in 2025) are anticipated to be more demanding on designers as the regulator drives towards net zero.

Approved Document F: ventilation

 Approved Document F aims to ensure adequate ventilation for building occupants’ well-being. Fresh outdoor air is essential for diluting indoor pollutants, and ventilation removes any excess water vapour generated by kitchens, bathrooms and human respiration. Building type classification must be checked within the Approved Documents guidance, as some exemptions also exist with certain building types (for example, buildings located within a designated conservation area).

Approved Document O: overheating

In the UK, building overheating is considered a significant risk to health and productivity, and the potential impact of overheating cannot be understated. Without appropriate assessment and management, rising global temperatures increase the risk of summertime overheating.

Approved Document O applies to new dwellings, including care homes and residential halls. Its guidance aims to protect building occupants’ health, welfare, and safety by reducing the occurrence of high indoor temperatures.

Creating a balance

Energy efficiency and ventilation

As we move towards a ‘fabric-first’ approach to seal buildings more effectively, the risk of reduced indoor air quality grows. Therefore, adequate ventilation must be considered. Where natural ventilation is not feasible or must be supplemented with mechanical ventilation, system commissioning is essential for balancing energy efficiency with optimal ventilation.

Conserving energy and thermal comfort

As with ventilation, energy conservation must be balanced with achieving acceptable thermal comfort levels. Building Services Research and Information Association (BSRIA) TG 22/2023 Thermal Comfort provides background on the basic principles of thermal comfort that apply to buildings in the UK.

Approved Document O guidance also outlines ways of designing and constructing a building to limit unwanted solar gains in summer while considering critical aspects of occupant safety and security. This includes limiting areas of glazing and providing fixed shading devices like shutters, external blinds, overhangs and awnings – all of which help remove excess heat from the indoor environment. Occupant safety measures include noise at night, pollution, security and protection from falls or entrapment.

Ventilation and thermal comfort via passive means

A balanced approach to building design is essential to reducing energy consumption while ensuring adequate ventilation and managing solar gain throughout the year. For example, space heating demand can be reduced in winter through the benefit of solar gain where it is available. In summer, reducing the glazed area can help reduce cooling requirements. However, reducing overheating in summer through limiting glazed areas also impacts winter solar gains, increasing the need for space heating. Approved Document O sets out guidance for the maximum glazed areas of a building, dependent on facade orientation and whether cross-ventilation is used.

Passive means of improving ventilation while limiting unwanted solar gains and removing excess heat should be strongly considered before mechanical cooling is adopted. It should be consistently demonstrated that passive means have been considered first. This includes specifying appropriately sized and oriented openable windows, creating cross ventilation where possible, or using mechanical ventilation fans instead of air conditioning.

Government schemes and incentives

UK government jurisdictions operate various schemes and incentives for more energy-efficient heating. As all government schemes are subject to updates and changes, specifiers should check relevant schemes with their local government jurisdiction before design.

As part of the UK Government’s drive for net zero, the Boiler Upgrade Scheme provides grants for domestic properties upgrading to air-source or ground-source heat pumps.

As part of the Scottish Government’s drive for net zero, the Home Energy Scotland scheme provides grants and loans for various domestic upgrades that make homes more energy-efficient. Additional financial assistance is available for rural properties. Eligible improvements covered by grants and loans may include:

Until now, the industry’s focus has been decreasing operational carbon, comprising approximately 70% of the built environment’s carbon emissions. However, the more energy-efficient our buildings become, the more impact operational carbon embodied carbon has. It is expected to eventually account for 70% of a building’s whole-life carbon rating. So, the next stage of our net zero journey must include ways to reduce embodied carbon.

  • Heat pumps.
  • Solid and cavity wall insulation.
  • Floor, loft and flat roof insulation.
  • Glazing.
  • Solar photovoltaic (PV) panels.
  • District heating connections.
  • Secondary improvements include wastewater heat recovery, smart controls, cylinder insulation and draughtproofing.

Several funding schemes require those delivering Energy Efficiency Measures (EEMs) to be TrustMark-registered and PAS 2030-certified. Specifications/ designs must comply with PAS 2035 and be installed as per PAS 2030 to receive funding. These include:

NBS article The retrofit standard framework provides more information on the retrofitting framework, PAS 2030, PAS 2035, and TrustMark. It also includes information on retrofitting for non-domestic buildings and PAS 2038.

The Energy Technology List (ETL) helps designers, energy managers and procurement professionals select more energy-efficient products. It is also relevant to owners and operators from an energy-saving perspective. The former Department for Business Energy and Industrial Strategy (BEIS) reviewed the ETL annually.

Final thoughts

As we strive to create a built environment that comes as close as possible to net zero, we need to look at the balances created by the systems we rely on for energy and human comfort. Passive means should always be the first line of consideration, followed by active means that can work together to reduce energy consumption. This can provide occupiers with a healthy and comfortable environment. For specifiers addressing these issues, NBS strives to provide Chorus with the information you need to make the best decisions for your project while meeting regulations. You can specify by performance or prescriptively, with generic or proprietary references. Clauses are editable and include extensive technical guidance to aid decision-making.

Chorus offers flexible plans with options to suit different budgets. For more information, contact one of our team members at info@thenbs.com.