England Part L 2021 - New Homes

19 July 2021 Kingspan Insulation UK
Image of new build houses

In early 2020, the Government completed a consultation on updates to Part L of the Building Regulations  for new homes in England (which govern conservation of fuel and power and ventilation). Earlier this year, it released its response along with the Future Buildings Standard consultation which, amongst other things, looked at additional requirements to prevent overheating in new homes.

These two documents have provided a clearer idea of what to expect when the final regulations are published (due by December 2021). Below are some of the key updates:

1.    31% carbon emissions reduction target

The headline change was that new homes will be expected to have 31% lower carbon emissions than under the current version of Part L. This is the more ambitious of the two options the Government put forward in its original consultation and a more reasonable stepping stone towards the Future Homes Standard, due to come into force in 2025, which will require an even greater reduction of 75-80% in CO2 emissions compared with current requirements.

2.    Primary Energy becomes the principal performance metric

As expected, the Primary Energy metric will replace CO2 as the principal performance metric. This metric is designed to consider not only the estimated energy demand of the property, but also how much energy is used in the various upstream activities needed to get it to the property. To achieve this, a Primary Energy Factor is applied to each fuel type based on how energy intensive its upstream activities are. In practice, this will mean that compliance with the Primary Energy metric will be simpler for certain fuel types than others. 

Learn more about Primary Energy 

Whilst the move away from just CO2 emissions (which is still a target) as the principal metric is a sensible step, it is disappointing that active monitoring will not be required within the new Part L. This seems like a missed opportunity to gain some useful data on whether the performance gap between designed and actual performance is being closed – a key step if we are to deliver net zero homes.

3.    Fabric Energy Efficiency Standards (FEES) retained

It was originally proposed that FEES (which limit the space heating demand for a house) would be removed in the new version of Part L. This led to concerns that homes could be built to lower fabric standards than at present with the underperformance masked through the use of renewables. In response to these concerns, the Government has now confirmed that FEES will be retained in the 2021 version of Part L for new homes. This is a positive move which should help to limit overall heating demand and ensure homes are more affordable to heat.

As part of the Future Building Standard consultation, the Government consulted on two options for FEES. Its preferred option would set these at the same levels as the tightened fabric notional dwelling specification (shown below1), whilst the second option would relax the overall target by 15%. 

NB FEES only considers the fabric elements, so roof, walls, floor, windows, doors, air permeability and thermal bridging (i.e. the elements affecting the heating energy demand) and is measured in kWh/m2 of floor area / year.
Element type Current (2013) notional dwelling 2021 notional dwelling use for Primary Energy, CO2 & FEES1 specification targets
All roof types1 0.13 0.11
Walls1 0.18 0.18
Floors1 0.13 0.13
Party wall1 0.00 0.00
Windows1 1.40 1.20
Doors1 1.00 / 1.20 (semi-glazed) 1.00
Air permeability1 5.00 m3/m2/Hr@50Pa 5.00 m3/m2/Hr@50Pa
Ventilation Natural with extract fans Natural with extract fans
Heating appliance 89.5% gas boiler 89.5% gas boiler2
Heat emitters Regular radiators Design flow temperature = 55°C
Photovoltaics No 40% of ground floor area

1 -Preferred option at same levels as the tightened notional dwelling specification
2 - New systems must meet 92% including adjustments for efficient controls

The new notional dwelling recipe itself shows only minor changes to the building fabric performances compared with the existing recipe, with U-values for roofs and windows lowered. To help futureproof homes for the move towards low carbon heating appliances (which operate at lower temperatures), it is recommended that heating systems are designed with a flow temperature no greater than 55°C. Waste water heat recovery (WWHR) and a Photovoltaic contribution are included in the new notional dwelling specification. Developers do not need to follow this specification, providing they meet all four target metrics for Part L 2021. The notional dwelling specification is just used to set these four targets:

1. Primary Energy target
2. CO2 emissions target
4. Minimum standards for fabric and fixed building services (discussed below)

4.    Minimum fabric standards tightened

To encourage a fabric-first approach to construction, the minimum mandatory requirements which all homes must meet have been notably improved:


Element type Current individual element area weighted limiting U-value (L1A 2013) Proposed new area weighted limiting U-values
All roof types 0.20 0.16
Walls 0.30 0.26
Floors 0.25 0.18
Party walls 0.20 0.20
Windows 2.00 1.60
Rooflights 2.00 2.20
Doors 2.00 1.60

This is a positive move which should help to avoid the need for fabric elements on new homes to be upgraded in the future. At the same time, it is important to note that these are the worst acceptable U-values for each element and that a home built to the above values would not comply with FEES.

5.    Approved Construction Details (ACDs) Removed

As part of efforts to address the performance gap between the designed and actual energy performance of homes, the standard ACDs will be removed and the ‘global’ adjustment taken when not following any details worsened.

All junctions should be designed and carefully reviewed to ensure buildability and to identify construction sequencing. Four options are available for assessing thermal bridges:

•    use construction details calculated by a suitably competent person following the guidance in The Building Research Establishment’s BR 497, and the temperature factors set out in the Building Research Establishment’s Information Paper 1/06;
•    use junction details from a reputable non-government database containing independently assessed thermal junction details, such as Local Authority Building Control’s Construction Details library;
•    use the backstop values in the SAP Table K1. A mixture of known and default values can be used; or
•    use a worsened default y-value of 0.20 W/(m2K) and compensate for this poor performance level elsewhere. 

We would strongly encourage installers and designers to engage with this process and look to develop the skills and knowledge to ensure correct detailing. Keep in mind that the default y-value and those within SAP table K1 represent a high level of heat loss through these junctions meaning performance in other areas may have to be notably improved over the notional dwelling.

6.    New compliance report introduced

A Building Regulations England Part L (BREL) consultation report will be introduced requiring a number of sign offs of the completed dwelling’s performance and regarding quality assurance and proof of commissioning. This will incorporate photographic evidence, for example, requiring details to be photographed before elements are concealed. The version of building regulations that a home was built to will also be incorporated into the information and the Energy Performance Certificate.

7.    Transitional Arrangements will apply per building

Under the transitional arrangements set to be introduced with Part L 2021, developers will only be able to construct homes to the existing Part L (2013) requirements if they have submitted building notice or deposited plans before June 2022 and have commenced work on the individual unit by June 2023. 

8.    Local authorities retain target setting powers

In another change from the original consultation, the Government confirmed that Local Authorities will retain their ability to set tougher local building performance regulations. However, it was indicated that these powers may be removed once the Future Homes Standard comes into force in 2025.

9.    Government proposes new Approved Document for Overheating

Finally, as part of the Future Buildings Standard consultation, the Government  recommended that a new Approved Document be created to specifically deal with overheating risk.

The consultation suggested two routes should be made available to achieve this: 
•    a simplified route - which sets a maximum glazing area and minimum open area (such as window openings) for ventilation based on the building type + location (Greater London has an additional shading requirement); and
•    a dynamic thermal modelling route – requiring a trained engineer to assess the overheating risk of the building under the methodology within CIBSE TM59.

Further Information
Learn more about Part L of the Building Regulations. 

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