Kingspan explores potential changes to Parts L & F

Kingspan explores potential changes to Parts L & F

Jonathan Ducker, Head of Regulatory Affairs at Kingspan Insulation UK, explores the potential revisions to Parts L and F of the Building Regulations.

This Spring major consultations into the energy performance standards for new homes have been undertaken in England and Wales. The revisions to Parts L and F of the respective Building Regulations are set to be implemented before the end of the year and are seen as a stepping stone to the introduction of even tougher requirements in 2025. With this in mind, it is important for developers to familiarise themselves with the proposals and consider how best to prepare for the likely changes ahead.

The consultations primarily deal with the mandatory requirements for the conservation of fuel and power, but the guidance for ventilation has also been revised alongside this; Approved Documents L1A (ADL1A) and Approved Document F are not mandatory, but provide guidance on how to meet the requirements of the Building regulations for new domestic buildings. The Part L guidance includes overall emissions targets and specific limitations such as worst-case U-values.

Targets for Part L1A

Both the English and Welsh consultations provide two uplift scenarios over their current versions of Part L1A. In England, the options are for a 20% or 31% (preferred) reduction on current carbon emission levels, whilst the Welsh consultation sets more ambitious targets: 37% (preferred) or 56%.

In addition, the consultations also introduce a new principal performance metric – Primary Energy – with carbon emissions retained as a secondary performance metric. The rationale for this is that as energy supply becomes decarbonised, CO2 will become a less important measure of property performance.

A Primary Energy Factor is first generated for each fuel type based on the energy used in upstream production activities such as extraction, processing/refining and transporting. Primary Energy for heating, for example, can then be calculated through the following equation:

(property energy demand/ efficiency of heating technology) x Primary Energy Factor

For example, take a property heated with 100% efficient electric panel heaters with an overall heating demand of 10,000 kWh. The fuel factor for electricity is 1.501 so Primary Energy is calculated as follows:

(10,000 kWh / 1) x 1.501 = 15,010 kWh

Energy generated by onsite renewable technologies such as photovoltaics (PV) can be used to reduce the energy demand calculation. For example, if PV is used to generate 1,500 kWh for use within the dwelling then the calculation would be changed as follows:

([10,000 kWh – 1,500 kWh]/1) x 1.501 = 12,759 kWh


Whilst the Primary Energy metric offers advantages, there are significant concerns about how it is implemented within the English consultation draft.

In the present English Approved Documents L, a Fabric Energy Efficiency Standard is used to limit the energy demand of the property. The consultation argues, however, that to prevent the standards becoming too complex, FEES should be removed entirely. In addition, the proposed worst-case backstops for fabric performance are laxer than even the current Welsh requirements.

In theory, this could allow homes to be constructed in England to the worst-case backstops across the board, with higher heat demand than one built to the current standards (and therefore subject to FEES), providing that this is compensated for by using lots of PV generation.

This approach isn’t very sustainable, nor very future-proof. As we decarbonise and move to electrified heating and hot water provision, reducing demands in the winter months will become increasingly important. Carbon intensities will be higher during these months as renewables are less efficient and demands are greatest. If we push more and more buildings, as well as transport, to the grid, there is a worry that unless demands are minimised, the carbon intensity at these times could even creep up (rather than reduce).

Fabric First

Overall, the better approach would be to take a fabric-first approach, maximising energy savings whilst retaining the ability to simply upgrade the building by adding energy generation in the future. Whilst not compulsory, the suggested building element U-values used within the notional building for the Welsh consultation offer a sensible starting point and, in meeting them, developers can upgrade their own design and building practices ready for 2025.

It is also worth noting that for English and Welsh consultations, thermal bridging and detailing will become more important. Under the proposed changes, the Approved Construction Detail’s associated generic psi-values (measure of heat loss through a junction) would be withdrawn, the global backstop default thermal bridging level would worsen and, unless developers have modelled/calculated psi-values available, the somewhat poor individual junction backstops will have to be used – so actually paying attention to detail will be very important to overall compliance. The two Welsh proposals and English 20% improvement scheme use the more stringent Option 1 values from SAP table R2 whilst the English 32% improvement options uses the more relaxed Option 2 values.

Looking ahead

Whilst the details of the English and Welsh ADLs are still to be finalised – the long-term trajectory is clearer. Very soon, developers will be expected to deliver dwellings which achieve net-zero emissions as standard. Whilst efforts to decarbonise the grid will support this, it is important that developers work now to reduce the energy demand from new homes. By adopting a fabric-first approach with careful detailing, companies can help to future-proof themselves for the changes ahead in 2025 and deliver high quality properties for homeowners.

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