Building Regulations Parts L and P

Part P deals with electrical safety in and around dwellings. Part L deals with energy performance, including fixed building services and on-site electricity generation. A domestic solar, battery, EV charger or heat-pump project can engage both, but for different reasons.

This entry covers England. Building standards are devolved, so the documents and notification routes are different in Wales, Scotland and Northern Ireland.

Regulations and Approved Documents

The legal requirements are in the Building Regulations 2010. Approved Documents give statutory guidance on common ways to meet them. An Approved Document is not the law itself, and following it does not guarantee compliance in every unusual case. An alternative approach can be possible, but it should be agreed with the building control body.

Saying only that work will be “to Part P” or “to Part L” does not identify the applicable requirements. The relevant evidence is the design, inspection, testing, commissioning, notification and certificates.

Part P: all fixed work must be safe

Requirement P1 calls for reasonable provision in the design and installation of electrical installations to protect people from fire or injury when operating, maintaining or altering them.

It applies to low- and extra-low-voltage fixed electrical installations in or attached to a dwelling, relevant common parts of blocks of flats, and associated gardens and outbuildings supplied from the dwelling. It includes rooftop PV and outdoor fixed equipment.

Approved Document P points to BS 7671 as the normal technical route for design, inspection and testing. BS 7671 is not itself a statute, and the old edition printed in the 2013 Approved Document is no longer the working edition. The electrical design should use the edition of BS 7671 applicable to the work.

New work does not automatically force every older part of the installation to be upgraded. The existing supply, consumer equipment, protection, earthing and bonding must, however, be suitable for the addition. Unsafe existing conditions may therefore have to be corrected before a new inverter, charger or heat pump can be connected.

Which electrical work is notifiable?

Under the rules described in the current Approved Document P, notification is required for:

• installation of a new circuit
• replacement of a consumer unit
• an addition or alteration to an existing circuit in a defined special location

Other fixed electrical work remains within Part P even when it is not notifiable. It still has to be properly designed, inspected, tested and certificated.

Solar PV, battery systems, EV charge points and heat pumps commonly require a new circuit and are therefore commonly notifiable. The legal test is the work actually carried out, not the product label. For example, connecting equipment to a suitable existing circuit may have a different notification position from installing a new circuit for it.

Notification and certification routes

Approved Document P describes three routes for notifiable work:

1. a person registered with an authorised competent person scheme self-certifies the work
2. a registered third-party certifier is appointed before the work begins, where that route is available
3. the building control body is notified before work begins and determines the inspection and testing needed

The first is common for domestic installations. The government’s live competent-person register identifies the authorised scheme operators and scopes. A logo does not establish the business or individual’s relevant registration.

MCS certification and Part P registration are separate. An MCS contractor may employ or subcontract a suitably registered electrician, but MCS status alone is not proof that the person completing the electrical work can self-certify it.

Electrical documents to keep

For a typical new-circuit installation, the handover file should contain:

• the appropriate BS 7671 Electrical Installation Certificate and schedules of inspection and test results
• a Building Regulations compliance certificate from the competent person scheme, or the completion/final certificate from building control
• the final circuit and isolation information, labels and operating instructions
• any design evidence for the existing supply, consumer unit, earthing and protective devices

The electrical certificate and the Building Regulations certificate do different jobs. Keep both. An MCS installation certificate, DNO response or manufacturer commissioning sheet does not replace either one.

Part L in an existing home

Adding energy equipment does not generally require an existing home to meet every new-build Part L target. It does mean that the affected fixed building service or on-site electricity system must meet the requirements relevant to that work.

Under the Part L guidance applicable as at 22 July 2026:

• a new or replacement heat pump is a fixed building service, so its efficiency, sizing, controls, installation, commissioning and owner information matter
• a heating design should be based on an appropriate heat-loss calculation and should not be significantly oversized
• a completely new or fully replaced wet heating system should be sized to work at a maximum flow temperature of 55°C or lower where feasible
• on-site generation and storage, such as PV and batteries, should be appropriately sized for the site, infrastructure and on-site demand and installed to the manufacturer’s instructions
• generation needs suitable controls and, where required, commissioning and owner information
• the energy performance of the service or generation affected by work in an existing dwelling should be assessed and documented

The 55°C point applies to a new or fully replaced wet heating system in the named Approved Document. It is not a blanket statutory maximum for every retained radiator system, nor proof that 55°C is the best heat-pump design temperature.

Part L can also apply directly when work replaces or renovates roofs, walls, floors, windows and other thermal elements. Those fabric requirements are separate from the fact that solar panels or a heat pump are being added.

Part L, solar and batteries

Part L’s on-site electricity requirement is about more than whether PV generates. It addresses appropriate sizing, available infrastructure, controls, commissioning and information for the owner. Approved Document L also discusses storage alongside generation because controls determine where generated electricity is used.

That does not replace the solar-specific requirements in MIS 3002, BS 7671 or the DNO process. A Part L record and an MCS certificate answer different questions.

For work on an existing home, retain the design and commissioning information showing the system actually installed. A new EPC is one possible form of broader energy-performance evidence in some circumstances, but it is not a universal handover substitute for the technical records.

Which Part L edition applies?

As at 22 July 2026, the normal current guidance is Approved Document L, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments, subject to its transition rules.

The government has also published the 2026 edition for the Future Homes and Buildings Standards. Publication does not make it the present requirement:

• it takes effect on 24 March 2027 for building work not connected with higher-risk building work
• it takes effect on 24 September 2027 for work connected with higher-risk building work
• the regulations contain transitional provisions for qualifying work already notified or approved and started by the relevant deadline

The 2026 regime adds a new functional requirement, L3, for renewable electricity generation at new dwellings and buildings containing dwellings, and revises the energy and greenhouse-gas requirements. It also gives updated guidance for heat pumps, electricity storage, commissioning and owner information.

This future position should not be turned into a present-day claim that every new or existing home must already have a fixed area of solar panels. The applicable edition depends on the type of work, its building-control route and the transitional dates.

Heritage buildings

Part L allows limited flexibility for listed buildings, buildings in conservation areas and scheduled monuments where full compliance would unacceptably alter character or appearance. It is not an automatic exemption from every energy requirement and should be agreed with building control and, where relevant, the conservation officer.

Part P has no equivalent general heritage relaxation. Electrical safety still has to be achieved, although cable routes, equipment positions and penetrations may need a design that also respects the building.

Planning permission and listed building consent are separate from Building Regulations approval.

Other requirements still apply

Depending on the project, other Building Regulations parts can cover structure, fire safety, moisture, ventilation, overheating, access and EV charging infrastructure. Building Regulations also sit alongside:

• BS 7671 electrical requirements
• MCS installation standards where MCS certification is sought
• G98, G99 and G100 network procedures
• planning and listed-building controls
• product safety and smart-charging rules

A single certificate should never be assumed to cover all of these regimes.

Notifications and completion records

Before work begins, confirm:

• which Part P notification route will be used
• who will issue the electrical and Building Regulations certificates
• which Approved Document L edition and transition applies, if Part L work is involved
• what heat-loss, sizing, controls and commissioning evidence will be supplied for a heat pump
• what sizing, control and commissioning evidence will be supplied for PV or storage
• which separate planning, MCS and DNO records are included

Related entries

• BS 7671 IET Wiring Regulations
• Consumer unit capacity
• MCS installation standards
• PAS 63100 domestic battery fire specification
• DNO notification for PV
• EVs Smart Charge Points Regulations