The first update to Part L of the Building Regulations in nearly a decade, and next step on the road to Future Homes Standard aiming to make sure all new homes built from 2025 produce around 75% less carbon emissions than those constructed under current regulations, with final goal of net zero in 2050.

As of 15 June 2022, the guidance will change due to the Building Regulations etc. (Amendment) (England) Regulations 2021 and the following two approved documents will be in force:

  • Approved Document L, Conservation of fuel and power, Volume 1: Dwellings
  • Approved Document L, Conservation of fuel and power, Volume 2: Buildings other than dwellings

When does a project fall under new requirements?

Part L changes will not apply in relation to building work where an initial notice has been submitted before 15 June 2022 provided that the building work is started before 15 June 2023.

Any Initial Notices submitted after 15 June 2022 must adhere to the new interim Part L standards.

The transitional process will apply to individual buildings, not across an entire site. Even if entire site covered by one Initial Notice submitted before June 2022, work not commenced on buildings within that site by June 2023 will fall under revised Part L requirements.

For the purposes of transition, commencement will not change from the existing 2013 definitions:

  • Excavation for strip or trench foundations or for pad footings.
  • Digging out and preparation of ground for raft foundations.
  • Vibrofloatation (stone columns) piling, boring for piles or pile driving.
  • Drainage work specific to the building(s) concerned.

The interim period from June 2022 is designed as a stepping stone to more stringent standards with next Part L update in 2025.

Requirements of Revised Part L

At least a 31% reduction in emissions compared to current standards. Alongside this, Part F, which governs ventilation, also updated.

Emphasis is on the adoption of a fabric first approach, with higher minimum fabric standards for the external envelope and improved airtightness, along with the use of low-carbon heating technologies. The maximum permitted U-values in the 2022 Part L is decreased slightly, ahead of more stringent decreases in 2025.

Notional Dwelling Specification for New Dwelling
Element or System Reference value for target setting Maximum fall-back value
External walls including semi-exposed walls 0.18 W/(m²·K) 0.26 W/(m²·K)
Party walls 0.0 W/(m²·K) 0.20 W/(m²·K)
Floors 0.13 W/(m²·K) 0.18 W/(m²·K)
Roofs 0.11 W/(m²·K) 0.16 W/(m²·K)
Doors 1.0 W/(m²·K) 1.6 W/(m²·K)
Windows and Glazed Doors(+60%) 1.2 W/(m²·K) 1.6 W/(m²·K)
Limiting U-values for new or replacement elements in new and existing buildings
Element Type Maximum U-value
Roof (flat) 0.18 W/(m²·K)
Roof (pitched) 0.16 W/(m²·K)
Wall 0.26 W/(m²·K)
Floor 0.18 W/(m²·K)
Windows in buildings similar to dwellings 1.6 W/(m²·K) or Window Energy Rating Band B
All other windows, roof windows, curtain walling 1.6 W/(m²·K)
Roof lights 2.2 W/(m²·K)

A new performance metric is introduced. Target primary energy rate, an annual figure measured in kWhPE/m², is the principal measure, which takes account of upstream energy production alongside the efficiency of a home’s heating system.

The primary energy metric has been developed to provide a more accurate measure of overall energy usage, considering both the energy needed to prepare a fuel for use and the final energy demand of the property.

Maximum air-permeability will be reduced from 10m³/(h-m²) to 8.0m³/(h-m²) at 50Pa, or 1.57m³/(h/m²) at 4Pa. An Airtightness Test for all dwellings will be mandatory, no averages permitted.

Also a focus on closing gap between specified and as-built performance, with greater scrutiny of build quality. In England, this will mean the introduction of Building Regulations Part L compliance reports (BREL) for dwellings and the need for photographic evidence of compliance.

2022 Part L requirements retain target carbon dioxide emission rates and target fabric energy efficiency rates, but these will eventually become obsolete as the energy grid decarbonises.

The latest version of SAP calculations incorporates various changes to the methodology.

For existing buildings, a simplified version of SAP called Reduced Data SAP (RdSAP) is used to assess the energy performance. An RdSAP assessment will use a set of assumptions about the building based on conventions and requirements at the time the building was constructed. Government is working on an RdSAP update which is expected in Spring 2022.

New Approved Document Part O – Overheating.

Deals with overheating in domestic dwellings and residential like commercial properties such as care homes and student accommodation. Buildings should make reasonable provision to:

  • Limit unwanted solar gains in summer
  • Provide an adequate means to remove heat from the indoor environment

Compliance with this requirement can be shown by using one of the following two methods:

  • The Simplified Method, as set out within Section 1 of the Approved Document O.
  • The Dynamic Thermal Modelling Method, as set out within Section 2 of the Approved Document O.

With introduction of new regulations and SAP 10, Approved Construction Details have been removed, and designers will need to detail their drawings to a certain specification such as those from manufacturers, or bespoke calculations will have to be made for each junction. Many insulation manufacturers publish details specific for their products.

Future Homes Standard and Heat Pumps

The Future Homes Standard, set to be implemented in 2025, is expected to ban use of heating systems exclusively designed to operate on fossil fuels in new homes. The proposals will encourage installation of ground source heat pumps which will allow solar panels to be removed from design and enable greater flexibility in the specified U-Values of individual thermal elements. Revised Part L won’t see an immediate rush to install heat pumps, due to skills and supply not yet up to scale.

As well as ensuring homes produce 75% less CO2 than current standards, the Future Homes Standard will mean “heat pumps…become the primary heating technology for new homes”.

This, in conjunction with the decarbonisation of the energy grid, will move the country away from gas-powered heating. From 2025, new homes will not be connected to the gas network.

Although hydrogen is likely to play a part, indications are Government will be investing the majority of its energies in promoting heat pumps through its future policies.

As well as heat pumps, an increase in the use of solar photovoltaic (PV) panels expected.

Spring 2023 will see launch of a Technical consultation on the proposed specification for the Future Homes Standard, with regulations being made in 2024 for implementation in 2025.

Lower and zero carbon future for all UK housing stock

Longer-term, a drive for lower-carbon energy in homes rolled out more extensively to UK’s current housing stock is expected. Following the Green Homes Grant, other incentive programmes expected to follow to encourage investment required to get UK to a zero-carbon future.

Changes to Approved Document F

The changes announced on 15 December 2021 to Approved Document F coincide with the changes to Approved Document L and the introduction of Approved Document O.  This is a result of the government’s announcements with changes to the Building Regulations to assist in delivering zero carbon ready homes in line with the Future Homes Building Standards in the UK from 2025.

All new residential buildings will be required to be designed to reduce overheating, improved ventilation to support the safety of residents in new build homes along with the prevention of airborne viruses spreading within new non-residential buildings.

The 2021 changes to Approved Document F see the document being split into two volumes; Volume 1 for dwellings and Volume 2 buildings other than dwellings.  The following should be noted:

  • Rooms for residential purpose  and buildings that contain only rooms for residential purpose should follow guidance under Volume 2.
  • Communal rooms that provide facilities for residents in a block of flats (eg laundry rooms, gyms) should follow guidance under Volume 2.  Note communal rooms does not include communal corridors/lobbies ie areas used mainly for circulation.
  • Live/work units should follow guidance under Volume 1 if the commercial part can be reverted to domestic use which requires all of the following to apply:
  • Direct access between the commercial space and living accommodation
  • Both the commercial space and living accommodation are within the same thermal envelope
  • The living accommodation makes up a substantial proportion of the total area of the unit.

The tighter air permeability requirements provides a greater emphasis on ventilation provisions and opting for the best suited system/method to achieve the required air changes for maintaining air quality….“Air Tight; Vent Right”

Approved Document F Volume 1: Dwellings

  • The new guidance no longer contains a specific section for new dwellings nor does it provide tables for the different type of systems. However system-specific guidance is provided which comprises of three systems (taken from Table 1.6):

Natural Ventilation:                                                            Less airtight dwellings

Continuous mechanical extract ventilation:           All dwellings

Mechanical ventilation with heat recovery:            All dwellings

Expert advise is required where situations outside of the above to ensure effective ventilation is provided.

A dwelling that is les airtight is one that has one of the following:

  • A design air permeability higher than 5m3/(h.m2) at Pa50
  • An as-built air permeability higher than 3m3/(h.m2) at Pa50
  • Guidance on minimising the ingress of external pollutants by ventilation systems now has its own section within the Approved Document (AD); Section 2 and includes the guidance values of pollutants referenced.

Work on Existing Dwellings

The guidance on work to ventilation on existing dwellings has been revised.

It stipulates that many existing dwellings are ventilated through infiltration rather than purposeful ventilation and as such, works to an existing dwelling could reduce the infiltration which may result in an under ventilated dwelling.

  • Where work carried out on a dwelling includes carrying out energy efficiency measures an assessment is required to determine if additional ventilation provisions are needed.  As such the guidance advises that an assessment should be carried out by:
  • Applying the simplified method. The simplified method is set out in the AD (Paragraphs 3.8 -3.13) which includes calculating the number of major and minor energy efficiency measures involved using the table provided (Table 3.1).
  • Seeking expert advice. Note that this may include an air test being carried out in accordance with Approved Document L Volume 1.
  • Following BSI PAS 2035

Works that involve installing energy efficiency measures fall into four categories:

  • Roof insulation
  • Wall insulation
  • Replacement of windows and doors
  • Draught-proofing (other than openings)
  • The current Approved Document advises that where existing windows do not have trickle vents, then it would be good practice to provide them or equivalent means thus only being a recommendation. However, where a building’s ventilation provision is not provided by a mechanical ventilation system replacing windows without background ventilators  may reduce the ventilation (ie worsening the ventilation provision prior to works being carried out).  This is due to the likelihood that airtightness is increased when replacing windows.   It is “necessary” to ensure the ventilation provision is made no worse.

The new guidance advises providing background ventilators to the replacement windows as a way to demonstrate that the ventilation provision has been made no worse.   See below table for the current and new minimum equivalent areas.

Current  Minimum Equivalent Areas New Minimum Equivalent Areas
Habitable Rooms 5000mm2 8000mm2
Kitchen 2500mm2 8000mm2
Bathroom (with or without a toilet) 2500mm2 4000mm2
Utility Room 2500mm2 N/A
Dwellings with continuous mechanical extract installing background vents in any replacement windows that are not wet rooms N/A 4000mm2

The alternative to not installing background ventilators to replacement windows is  by other ventilation provisions if it can be demonstrated to the building control body that they comply with requirements of 3.2.

Approved Document F Volume 2: Buildings Other Than Dwellings

  • Occupiable rooms in offices
  • Occupiable rooms where singing, loud speech, aerobic exercise or other aerosol generating activities to take places eg gyms, theatres, places of assembly etc
  • Occupiable rooms where members of the public are likely to gather eg public buildings, pubs, places of assembly etc
  • Occupiable rooms which are maintained at both low temperatures and low levels of humidity eg occupied cold stores

Rooms that fall into either of the following are not applicable:

  • Small spaces/rooms: Upto 125m3 volume or 50m2 floor area
  • Large spaces/rooms: Over 800m3 or 320m2 floor area

The following definition of an occupiable room is given in Approved Document F Volume 2:

“A room in a building other than a dwelling that is occupied by people, such as an office, workroom, classroom or hotel bedroom.  The following are not occupiable rooms: bathrooms, sanitary accommodation, utility rooms or rooms or spaces used solely or mainly for circulation, building services plant or storage purposes.”

  • CO2monitoring  is cited as being a means of measuring indoor air quality.  CO2 monitoring can assist identifying areas poorly ventilated areas.  Where CO2 monitors are used the following should be met:
  • Be non-dispersive infrared (NDIR) type monitors
  • Be mains powered
  • Be located at breathing height and away from windows, doors or ventilation openings where practicable.
  • Be placed at least 500mm from people where practicable.

The guidance also provides information on the type of CO2 monitor to use, how to use the monitor, how to attain the most accurate readings, how the findings can help you to take action as well as which type of areas that are less effective.

  • The Approved Document now includes guidance on ventilation systems that recirculates air between more than one space/room/zone.  Where air is recirculated between more than one space/room/zone it should be able to operate in a mode that reduces the risk of transmitting airborne infections  by
  • Systems with a 100% fresh air mode
  • Systems that incorporate UV-C germicidal irradiation
  • Systems designed so that they are able to incorporate HEPAfiltration if required
  • Guidance on minimising the ingress of external pollutants by ventilation systems now has its own section within the Approved Document (AD); Section 2 and includes guidance values of numerous pollutants.  Added pollutants to the list: fomaldehyde, ozone and TVOC.

The replacement window guidance has been revised in the same manner as dwellings.  See below table for the current and new minimum equivalent areas.

Current  Minimum Equivalent Areas New Minimum Equivalent Areas
Occupiable Rooms – up to 10m2 2500mm2 2500mm2
Occupiable Rooms – greater than 10m2 250mm2 per m2 of floor area 250mm2 per m2 of floor area
Domestic Type Kitchen 2500mm2 8000mm2
Bathroom (with or without a toilet) and Shower Rooms 2500mm2 per bath or shower 4000mm2 per bath or shower
Sanitary Accommodation (and/or a washing facility) 2500mm2 per WC 2000mm2 per WC

The alternative to not installing background ventilators to replacement windows is  by other ventilation provisions if it can be demonstrated that they comply with requirements of 3.2.

If you would like to attend one of our CPD Webinars dealing with the Summary of Revised Part L F & O of the Building Regulations please register below: