Part L 2021 - New non-domestic buildings in England

13 October 2021 Kingspan Insulation UK

At the start of 2021, the Ministry of Housing Communities and Local Government (MCHLG) launched a new consultation looking at changes to Part L and F of the Building Regulations for non-domestic buildings in England. These sections set the requirements for energy performance and ventilation. In this blog, we look at some of the key changes that have been proposed for new non-domestic buildings.

1.    CO2 uplift options

The consultation offers two options for upgrading the carbon emissions targets for new buildings:

•    Option 1 – a 22% improvement over the existing version of Part L. This will be achieved through improved building service efficiency and the use of on-site low carbon technologies including heat pumps and solar photovoltaics; and 

•    Option 2 – a 27% improvement over existing Part L requirements to be achieved through very high fabric standards along with improvements to building services and the use of onsite low carbon technologies. 

Option 2 is the Government’s preferred solution and, in focusing on fabric performance, should provide a better option for limiting the energy demand of new non-domestic buildings over the long-term without overly relying on renewable technologies 


2.    Primary Energy metric introduced

As with all of the 2021 Part L documents, the consultation for new non-domestic properties suggests the introduction of Primary Energy as the new principal energy performance metric. This metric provides an estimation not only of the energy used by a property, but also the total energy used in upstream processes. 

Learn more about Primary Energy. 

CO2 emissions are retained as a secondary performance metric, supporting the government’s overall commitment to reach net-zero carbon performance in the UK by 2050.


3.    New minimum requirements for fabric and services

To ensure a good level of fabric performance from all new buildings and thereby reduce energy demands, the final performance metrics used are minimum fabric and services requirements. The proposed changes for the building fabric are shown below:
Element type Current new element area weighted limiting U-values (L1A 2013) Proposed 2021 new element area weighted limiting U-values
All roof types N/A N/A
- pitched roof (sloping) 0.25 0.16
- pitched roof (horiz) 0.25 0.16
- flat roof 0.25 0.18
Walls 0.35 0.26
Floors 0.25 0.18
Swimming pool basin 0.25 0.25
Windows 2.20 1.60 or window energy rating B
Other windows 2.20 1.60
Rooflights 2.20 2.20
Pedestrian doors including glazed 2.20 1.40
Vehicle access and similar large doors 1.50 1.30
High usage entrance doors 3.50 3.00
Roof ventilators (inc. smoke vents) 3.50 3.0
Air permeability 10.00 m3/m2/Hr@50Pa 8.00 m3/m2/Hr@50Pa
(or 1.57 m3/m2/Hr@4Pa via Pulse testing)

The minimum requirements for new non-domestic buildings in England have lagged behind those set within other regions and it is positive to see that they have been notably tightened within the consultation recommendations. Keep in mind that these are the minimum requirements for each individual element and that a building built to the above specification would not achieve compliance with the new version of Part L.


4.    Thermal bridging

It is also positive to see that the default assumptions for thermal bridging within SBEM will be worsened. This will effectively punish projects which choose to rely on these values rather than carrying out accurate detailing. By encouraging best practice in this area, we should be able to close the performance gap between the designed and actual energy performance of buildings.  

5.    Changes to National Classification Methodology (NCM) and Notional Building

The consultation also proposes updates to the NCM. The NCM works by creating a notional building of the same dimensions as the planned structure with standardised fabric and service properties. The Primary Energy demand and CO2 rate for the property are then calculated using the fuel type selected for the building. The resulting values set the Primary Energy and CO2 emissions targets for the building. 

The proposed standardised fabric and services properties for the notional building within Part L 2021 Non-Domestic England are shown below. The actual specification used to reach these can vary (providing it also meets the minimum fabric and services requirements).

Option 2 for side-lit and unlit activities is the Government’s preferred notional building package in the recent consultation, but option 1 is also under consideration. There is a separate package for top lit activities, which covers buildings such as warehouses, where there is no or minimal heat demands, so the building fabric has less of an impact on overall energy demands.
Element U-Value (W/m2K) Thermal capacity (kJ/m2K)
  Option 1 for side-lit and unlit activities Option 2 for side-lit and unlit activities Top-lit activities  
Roofs (irrespective of pitch) 0.18 0.15 0.18 88.3 (1.40 if metal clad)
Exposed walls 0.26 0.18 0.26 21.8 (1.40 if metal clad)
Exposed floors and ground floors 0.22 0.15 0.22 (unless uninsulated is better) 77.7
Windows and glazed doors 1.60 1.40 - -
Roof-lights - - 2.10 -
Vehicle access and similar large doors 1.30 2.1
Pedestrian doors and high usage entrance doors 1.90 54.6
Internal walls 1.80 8.8
Internal floors / ceilings 1.00 71.8 from above / 66.6 from below
Air permeability for the Notional building (m3/h per m2 of envelope area at 50 Pa) 5 3 5 N/A

6.    Design-For-Performance Approach

The consultation also discusses the issue of the performance gap between the expected and actual energy performance of buildings in detail, noting that the outputs from the 
Part L compliance calculations are not suitable for energy benchmarking as they do not consider all energy uses within a building and rely on standardised usage data.

For this reason, in addition to Part L compliance calculations, it will also be required that forecast energy performance is modelled for buildings with a floor area over 1,000 m2. This forecasting would be carried out in line with the process in CIBSE TM54, requiring monthly energy usage figures (kWh) to be broken down into fuel type and end energy-use categories. This forecast will be provided to the building owner at handover. In addition, the Government has also committed to consulting on introducing mandatory in-use energy ratings for buildings.

The move toward mandatory forecasting and, potentially, in-use monitoring is a much needed step if we are to close the performance gap. At the same time, it is disappointing that this measure is not identified as a key metric and no mechanism is suggested to require underperformance to be addressed. 

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