Part P, Part L and Part F: What Each One Means for Your Trade

‍‌‌‌‌‌‌​‌‌‌‌​‌‌​‌‌‌​​​​‌​​‌​‌‌‌‌‍SiteKiln gives you plain-English information, not building control advice, design guidance or a substitute for reading the Approved Documents. If you need advice specific to your project, check with your building control body.

7.11.1 The short version

Part P, Part L and Part F are three chunks of the Building Regulations 2010 that quietly wreck a lot of jobs: electrics (P), energy (L) and ventilation (F). You can build a lovely extension that looks fine and still fail on any one of these.

Part P is about electrical safety in dwellings, Part L is conservation of fuel and power (insulation, airtightness, heating), and Part F is ventilation (getting stale, damp air out and fresh air in). Miss them and you either don't get sign-off or the client ends up with a cold, mouldy, dangerous box that comes back to haunt you.

7.11.2 Part P -- electrical safety in dwellings

Part P says domestic electrical work must be designed and installed so it doesn't present a risk of fire or electric shock, and it sets the rules on notifiable work.

Key points:

• It applies to low-voltage and extra-low-voltage electrical installations in or attached to dwellings, plus shared parts and outbuildings fed from them.
• Certain jobs (new circuits, consumer unit changes, work in specific locations, etc.) are notifiable and must be either:
  • Notified to building control, or
  • Self-certified by a Part P scheme electrician (NICEIC, NAPIT etc.).

Typical ways people get caught:

• Letting unregistered sparks do notifiable work and never notifying -- then building control or a surveyor spots it later.
• Assuming Part P doesn't apply to garages, conservatories or sheds because "they're separate" -- they usually are covered if fed from the house.

7.11.3 Part L -- conservation of fuel and power

Part L is the energy bit: insulation, airtightness and efficient fixed services.

The requirement is "reasonable provision" to limit heat loss/gain and provide efficient fixed building services. In practice, for houses and extensions that means:

• Meeting U-value targets for walls, roofs, floors, windows and doors.
• Hitting SAP targets for new dwellings (emissions, fabric energy efficiency, airtightness).
• Using efficient boilers/heat pumps, controls, hot water systems, lighting and so on.

Where builders trip up:

• Building what's on old planning drawings, not what's on the SAP / Part L design -- wrong insulation thickness, wrong glazing spec, no thought for thermal bridges.
• Forgetting airtightness and commissioning -- you can fail on blower-door tests or services that haven't been properly set up and signed off.

7.11.4 Part F -- ventilation

Part F is about ventilation -- getting rid of moisture and pollutants while keeping the place comfortable.

The basic requirement is that a dwelling must have means of ventilation that:

• Extract water vapour and pollutants from kitchens, bathrooms, utilities and WCs.
• Provide background and whole-dwelling fresh air.
• Work properly with whatever energy/airtightness measures you've installed.

Common traps:

• Beefing up insulation and airtightness (Part L) but not upgrading vents or extract -- result: condensation and mould, and failure on Part F.
• Relying on tiny or missing trickle vents in new windows when the latest guidance expects higher background vent areas per habitable room.
• Not commissioning or testing mechanical systems (fans, MVHR) to the flow rates Part F expects.

Recent revisions have tightened ventilation rates and expectations, not loosened them. If you make a home more airtight, you must think about Part F at the same time, not as an afterthought.

7.11.5 Quick P / L / F health check

You're less likely to get bitten by these three if:

You treat electrics, energy and ventilation as part of the design from day one, not "let's see what the spark and plumber do on site".

You use registered electricians for notifiable domestic work and make sure Part P notification is either through them or building control, not "we'll sort it later".

For new builds and proper extensions, you actually follow the SAP/Part L design for insulation, glazing, airtightness and heating, and keep evidence for building control.

Whenever you tighten up a house thermally (new windows, added insulation), you check what Part F expects for extract and background ventilation and plan that in.

If any of that is currently "we just copy what we did on the last one", that's where the risk sits.

7.11.6 What to do next

• Treat electrics (Part P), energy (Part L) and ventilation (Part F) as part of the design from day one, not afterthoughts.
• Use registered electricians for notifiable domestic work and make sure Part P notification happens through them or building control.
• For new builds and extensions, follow the SAP/Part L design for insulation, glazing, airtightness and heating -- do not copy old specs.
• Whenever you tighten a house thermally, check what Part F expects for extract and background ventilation and plan that in at the same time.

7.11.7 Who to contact

• Local authority building control -- for Part P, Part L and Part F queries, applications and inspections
• NICEIC -- 0333 015 6625, niceic.com -- for Part P self-certification and scheme queries (free to check)
• NAPIT -- 0345 543 0330, napit.org.uk -- for Part P self-certification and scheme queries (free to check)
• CSCS -- 0344 994 4777, cscs.uk.com -- for card and competence queries (free)
• Environment Agency -- 03708 506 506 -- for environmental queries on site (free)

7.11.8 Sources and legislation

• Building Act 1984 -- framework for building regulations. legislation.gov.uk/ukpga/1984/55
• Building Regulations 2010 -- Parts P, L and F. legislation.gov.uk/uksi/2010/2214
• Electricity at Work Regulations 1989 -- electrical safety duties. legislation.gov.uk/uksi/1989/635
• Environmental Protection Act 1990 -- environmental duties relevant to building work. legislation.gov.uk/ukpga/1990/43

7.11.9 Related guides on this site

• 7.4 NICEIC / NAPIT / Part P
• 7.10 Building regs vs planning permission
• 7.3 Gas Safe registration
• 7.14 MCS certification -- heat pumps
• 7.15 TrustMark registration
• 6.1 Public liability insurance

Common questions

Is Part P electrical self-certifiable?

Only if you're registered with a Competent Person Scheme such as NICEIC, NAPIT, ELECSA or Stroma. Registered electricians can self-certify notifiable work and issue the Building Regulations compliance certificate. Anyone else must notify Building Control, pay them to inspect, and have them certify it.

Part P Electrical Safety guide.

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