Summary
Adveco looks at the fundamental shift in UK regulations which are preparing the future of commercial buildings and considers their impact on the design and implementation hot water systems...
The UK’s commitment to achieving Net Zero carbon emissions by 2050 is driving a fundamental shift in building regulation. The impending Future Homes and Buildings Standard (FHBS), due to be fully implemented by the end of 2027, represents a significant uplift in energy efficiency and environmental performance requirements for non-domestic properties.
The new FHBS builds upon the interim 2022 uplift to Approved Document L (Conservation of Fuel and Power, Volume 2: Buildings other than dwellings), focusing on highly efficient, ‘zero-carbon ready’ non-domestic buildings. The core strategy for readiness involves a ‘Fabric First’ approach combined with a mandatory transition to low-carbon systems.
Embracing the Fabric First Approach
Future compliance will be heavily weighted on the building’s envelope performance. Consultants must advise clients to exceed current minimum standards well ahead of the 2025 deadline.
Consultants should specify maximum U-values that significantly outperform the 2022 standards for elements like walls, roofs, floors, and glazing. For new commercial projects, the tightening of U-values for windows and doors is particularly notable (e.g., from 2.2 W/m²K to 1.6 W/m²K in the 2022 update, with further tightening expected). The requirement for air permeability testing on all new buildings is mandatory. Consultants must specify designs that target an air-tightness rate well below the current maximum of 8.0 m³/(h·m²) at 50Pa (with expectations that the FHBS may tighten this further). This requires meticulous detailing and rigorous site supervision during construction. Accurate calculation of thermal bridging (psi-values) is also crucial, replacing reliance on default values. As such, detailed thermal bridging analysis should be completed at the design stage.
Decarbonise Fixed Building Services
The shift away from fossil fuel heating systems is also a core principle of the FHBS.
The low-carbon heating mandate will mean gas boilers are being effectively phased out in new commercial buildings. Consultants must move all new designs towards low-carbon heating technologies, such as high-efficiency air source or ground source heat pumps (ASHPs/GSHPs) or a connection to district heat networks when and where available.
New compliance metrics will move beyond just carbon emissions. The new methodology uses primary energy targets, measuring the total energy used, including generation and delivery losses, alongside CO² emissions targets. This metric heavily favours electrically powered, high-efficiency systems (such as heat pumps) and penalises traditional gas-fired systems.
The importance of operational performance assessment will also be taking centre stage as owner/operators need to prepare for greater scrutiny of as-built performance versus design performance. Tools like TM54 Operational Energy Assessments are highly recommended to model and predict the real-world energy consumption, minimising the ‘performance gap’ between design expectation and reality. Regular physical usage metering at the micro (appliance) and macro (building) levels will become truly advantageous.
Used for design support planning applications, and to satisfy industry requirements, document O and the updated Part F specify that glazing and ventilation are critical for non-domestic compliance. Under document O, designs must limit unwanted solar gains, especially in highly glazed buildings. Preventing overheating involves smart design choices such as brise-soleils, low-g-value glazing, and appropriate window-to-wall ratios. Part F addresses the need for enhanced ventilation in new commercial buildings, particularly offices. These require updated ventilation systems, often including air quality monitors such as non-dispersive infrared (NDIR) type CO² monitors and provisions to mitigate the transmission of airborne infections through recirculated air.
Hot Water Compliance: Balancing Safety and Efficiency
While domestic hot water systems will not be affected by the fabric-first principle, commercial properties will still face the dual challenge of meeting stringent energy efficiency targets (Part L) while rigorously controlling health and safety risks, primarily Legionella (Health and Safety Executive guidance, notably HSG274).
Energy efficiency strategies under Part L are designed to ensure the hot water plant contributes positively to the overall primary energy and CO² emission targets. Consultants are well-versed in this and will now typically aim to utilise heat pumps for hot water. This sees the integration of ASHPs or potentially ground or water source alternatives into the hot water production chain, rather than relying on just an electric boiler or immersion for new build or gas water heaters when refurbishing plant in existing buildings. This is now deemed essential for meeting low-carbon targets.
Correctly designing hot water systems to precisely meet peak demand without oversizing is necessary for avoiding excessive storage volume that wastes energy and adds considerably to a project’s capital and long-term operational costs. There have been, in recent years, considerable advances made in the prevention of oversizing; however, some applications are now suffering from undersizing. A 30kW energy source can heat 750 litres/hour by 34°C, so when the system draws hot water at a faster rate than it can be heated to 44°C, such as for hot showers, complaints of ‘cold’ water can be expected. This is a danger with systems deploying low-temperature ASHPs, which must therefore work harder, whilst driving greater use of ‘primary’ top-up heating. Electrical demand is managed by increasing the size of the hot water storage, which is then heated more slowly. Integrating a larger volume cylinder helps to overcome this undersizing, allowing for a two-hour reheat cycle that maintains enough water at 60°C to meet daily demand, whilst slowly heating reserves through the night when demand is minimal to meet the morning peak. This is a very different approach to the high energy input and low storage seen with traditional gas-fired systems.
All pipework and storage tanks must also be insulated to the highest possible standards to minimise waste through standing heat loss. Concerns over standing losses mean specification of instantaneous or point-of-use electric heaters for very low-use outlets or remote areas can be appropriate for avoiding running long, inefficient recirculation loops to little-used points, saving both energy and reducing Legionella risk. However, well-designed centralised systems with electric boilers and cylinder combinations will demonstrate similar or less standing losses, as well as being able to take advantage of low-carbon preheat, whether in the form of heat pumps or solar thermal. This contributes to the system’s ability to reduce dependency on energy, reducing carbon emissions and energy costs across its lifetime.
Health and safety, and especially Legionella compliance, remain absolutes. The key to hot water safety is temperature control and stagnation prevention. Owners and consultants must ensure the system is designed to facilitate ongoing management under the ACOP L8 and HSG274 guidance. The key is that commercial hot water storage cylinders (and calorifiers) must store water at 60°C or higher, and that the primary heat source can achieve this consistently, especially when using heat pumps, which can struggle to reach high temperatures efficiently. When distributing the hot water, it must reach a minimum of 50°C (55°C for healthcare) at all sentinel outlets (furthest/closest) within one minute. Designing effective hot water recirculation loops with temperature monitoring points and adequate pump sizing is therefore critical for maintaining flow and temperature throughout the system.
Water should not stand unused for sustained periods (a week or more) to prevent the development of Legionella. Normally, in hot water systems, the risk is minimised by the temperature, constant flow and because the risk of Legionella in the incoming mains is relatively low. However, it can be present, and the risk to building occupants increases if a water system is fed from a cold water tank instead of the mains.
Overall system cleanliness is very important, from a health perspective, but also to ensure system efficiency. Tanks and cylinders must be inspectable and drainable, so when specifying indirect cylinders (calorifiers), ensure drain valves or clean-out access allow for the annual removal of accumulated scale and particulate matter, which acts as a nutrient source for the bacteria.
Applications need to design out dead legs and dead ends in pipework where stagnation could occur, and the system design must accommodate regular, weekly flushing at high temperature, preferably more than 70°C, to curtail any possible development of Legionella, especially for all infrequently used outlets, such as vacant offices, school buildings over the holidays or seasonal facilities.
With the higher temperatures (50°C+) demanded of commercial applications, it is also important to ensure that protection from scalding is in place. Thermostatic Mixing Valves (TMVs) must be fitted as close as possible to the point of use to blend the water down to a safe temperature (typically 44°C or less) to prevent scalding.
Future UK building regulations demand a highly integrated and performance-focused approach. For consultants, this means mastering low-carbon technology and fabric detailing. For owners, it requires investing in quality installation and establishing rigorous monitoring and maintenance schedules. By proactively tackling the twin challenges of radical energy efficiency (Part L/FHBS) and stringent health and safety (hot water/Legionella), commercial building projects can ensure not only compliance but also long-term value, lower operational costs, and a safe environment for occupants.
Read more about Net Zero and water heating in commercial buildings
