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.
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.
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.
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.
The reduction of carbon emissions can be achieved by:
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.
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.
NBS Chorus guidance provides further detail regarding regulations as they apply to each country
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.
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.
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.