5th February, 2021

The Future Buildings Standard Part L2 2021

The long-awaited response to the Part L consultation was finally published on 19th January. The FES Group will be running a Technical Advice Session in due course to guide you through the changes and look at the implications for the industry.  

The FES Group have reviewed the response from Government on the proposed changes to Part L following the consultation on the proposed Future Buildings Standard.

Despite a notable delay due to the COVID-19 pandemic, the response has answered a number of questions and set-in motion the requirements of the interim update to Part L2 2021. It has also left some details yet to be confirmed. The FES Group will continue to provide updates over the coming weeks and months as the cSBEM software continues to be developed.

The FES Group also acknowledge the Government’s intention to accelerate the consultation on the Future Buildings Standard 2025, Which is planned to be implemented in 2024 with a 12-month transitional agreement. It is anticipated that Part L 2021 and cSBEM may only be applicable for a few years.

The following section will summarise notable changes that have been identified by The FES Group in our review of the latest Future Buildings Standard consultation document.

Part L 2021 Standards for Non-Domestic Buildings

Considerations were undertaken in the consultation to either deliver Option 1 – a 22% improvement in CO2 emissions per building, or Option 2 – a 27% improvement in CO2 emissions per building. The response to the consultation has strongly indicated the Future Buildings Standard will aim to achieve a considerable reduction over current standard with Part L2 2021 to implement a proposed 27% reduction in emissions over the current regulations. We await further clarification and will advise on this confirmed approach as soon as it is available.  

With consideration to the delay caused by the pandemic and additional government policies introduced within the last year The FES Group had anticipated this choice. We expect this would typically be delivered by very high fabric standards, resulting in lower levels of heat loss from windows, walls, floors and roofs, improved services such as lighting, and low carbon technologies such as heat pumps or photovoltaic panels.

The proven scalable solution for zero carbon heat is a decarbonised electric grid, which as a result puts electric as the anticipated main heating fuel for new buildings. This is based on the efficiencies provided by using air source heat pumps which are capable of generating 3 times the amount of heat compared to the energy used.

It was recognised that the industry has concerns with regards to the available supply chains, skilled personnel and increased pressure on infrastructure and it is stated that the construction industry will be required to implement these changes over the coming years in anticipation of the Future Buildings Standard update in 2025.

The consultation had proposed the use of 4 performance metrics over the previous 3 metrics currently used in SBEM calculations. The Building Emission Rate (BER) and Target Emission Rate (TER) are to remain as well as minimum standards for fabric and fixed building services, along with new addition of primary energy targets.

From 2021 the proposal is to introduce primary energy as the principal metric against which the energy efficiency of new buildings should be assessed, as the basis for the Part L performance target. A primary energy target would enable the ability to set an energy performance target which prioritises the energy efficiency of the building by driving efficiency in building technological solutions, and the energy efficiency of the building fabric regardless of the heat source.

Despite a new focus on primary energy, reducing the CO2 emissions of new buildings remains a key objective for the Government. Although the government considers primary energy to be a good means of driving energy efficiency, it may not drive low carbon choices in all scenarios. For this reason, the proposal is to continue to use CO2 targets for buildings alongside the primary energy target to encourage low-carbon fuel choices and the use of on-site renewable technologies.

The following 4 metrics will be implemented in Part L 2021

  • Carbon Emission Targets
  • Primary Energy Targets
  • Minimum Fabric Performance
  • Minimum Fixed Building Services Performance

Building Services

The consultation has outlined improvements to fixed building services minimum efficiencies, as well as changes to the current calculation methodology. Currently, the performance of the building HVAC system will be compared to a notional system of the same fuel type with a default efficiency. New proposals outlined that natural gas will be assigned to the notional building as the fuel type against any fuel with a worse emission factor, such as oil or LPG. Electric heating and anything with a better carbon emission factor than gas will be compared against the same fuel type. Specific fan powers (SFP) in (W/(l/s)) are set to reduce for extract/supply and applicable HVAC systems, and the minimum standards of all heating fuel seasonal efficiencies are to be improved, along with heating and cooling COP’s (coefficient of performance) and EER’s (energy efficiency ratios) of HVAC systems.

New Approved Document Part L, volume 2 information will outline guidance for appropriate sizing and control for proposed building services in order to reduce the over or under sizing of systems. It is also of importance to note that PV will be added to the notional building unless a heat pump meets 100% of the actual building’s space heat demand. This is intended to discourage excessive levels of photovoltaics in order to compensate for a building design that has not prioritised a high standard fabric specification and efficient fixed building services.

This approach has been taken to discourage the use of high-carbon fossil fuels within buildings, whilst still allowing for flexibility and diversity in design if performance can be feasibly compensated elsewhere within the specification. Electricity will have a lower carbon emission factor than fossil fuels, but on its own in a grid supplied system would likely result in high primary energy impact without the use of low carbon technology such as heat pumps, CHP or being part of a district heating network for delivery.

Minimum lighting standards are to be improved to reflect the improved performance and cost effectiveness of LED lighting, which are suitable for almost all indoor applications including display lighting. The minimum performance of general lighting is to be increased to 95 lm/cW (lumens per circuit Watt), and that of display lighting is to be 80 lm/cW (lumens per circuit Watt).

The consultation proposes that Building Automation and Control Systems (BACS) should be equipped to any building with an effective rated output of over 290kW.


It has also been confirmed that the limiting factors for fabric u-values are to be improved, however this is over and above the original consultations proposals. In most instances such values are already being achieved.

To confirm the proposed limiting u-values for Part L2 2021 are as follows:

  • Floor 0.18 W/m²K
  • External Wall 0.26 W/m²K
  • Pitched Roof 0.16 W/m²K
  • Flat Roof 0.18 W/m2K
  • Windows 1.60 W/m²K or Windows Energy Rating Band B
  • Pedestrian Doors 1.60 W/m²K
  • Vehicular Access or similar large doors 1.3 W/m²K
  • High Usage Entrance Doors 3.0 W/m²K
  • Rooflight 2.20 W/m²K (Horizontal Plane)
  • Air Pressure Test 8.00 m³/m².h

Regarding fabric detailing, the performance of default thermal bridging values for non-domestic buildings is to be reduced in order to encourage designers to take more consideration of thermal bridging performance within commercial designs, which already has more of a considerable impact within domestic SAP calculations. Proposals also seek to increase solar performance requirements by improving the performance of reference glazing in the notional building by providing better g-value performance. The FES Group will provide more updates on this when the effect on overall performance is better understood.

Finally, The FES Group are pleased to see the confirmation of the updated u-value methodology to BR443 (2019).

Air Tightness

The consultation has confirmed that the methodology will be written by CIBSE in the form of CIBSE TM23 for both domestic and non-domestic buildings. The maximum allowed air tightness target is set to be reduced.

The consultation has also confirmed that the maximum allowable air test to an 8.00m³/m².h will be introduced. However, the proposals to round up all as built Air Testing results within the SBEM calculation to the nearest 0.5 m³/m².h will not be introduced. The FES Group welcome this as accurate, as tested results represent an accurate input of results within the calculation.

It was also confirmed that an alternative air testing method will be introduced in the form of the Pulse Air Testing Unit. Again, this is welcomed as it provides a different option for air testing beyond the current blower door method.

Compliance, Performance and Providing Information

There is currently no information to suggest that the current system of the provision of a BRUKL document at As Designed and As Built stage followed by the EPC upon building completion is going to change.

In October 2019, the Government announced the intention to consult on mandatory in-use energy ratings for non-domestic buildings. Proposals are to continue to use CIBSE TM39 as the standard to which new buildings should be sub-metered. As well as this, the implementation should allow useful comparison between in-use and design stage energy-use forecasts such as CIBSE TM54. This is intended to allow buildings to diagnose and fix energy performance when the building is in use. The FES Group will comment further as this situation develops.

Proposals are to introduce requirements for when a new heating/ HVAC system is installed in a non-domestic building. Overall energy performance of the system will be assessed and documented, with results passed on to the building owner as part of the commissioning process.

It has been confirmed that the cSBEM calculation methodology is now available for public consultation. The FES Group will continue to assess the impact of the change and offer our initial advice on the implications of the new edition of the regulations.

Report by Jack Park, Sustainability Consultant
For and on behalf of The FES Group
Details of our Technical Advice Session regarding Part L2 2021 will follow shortly.

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