Building Regulations Overview: Which Parts Apply to Which Jobs?

Quick Answer: Building Regulations in England are divided into Approved Documents (Parts A–S). Most building work on existing dwellings requires compliance, but not all work requires a formal notification or application. The threshold is whether the work is "building work" as defined in Regulation 3 — which includes new structures, extensions, material alterations, and changes of use — versus maintenance and like-for-like replacement.

Summary

Building Regulations exist to ensure the safety, health, welfare, and convenience of people in and around buildings. They set minimum standards for structural integrity, fire safety, energy efficiency, ventilation, drainage, and dozens of other technical requirements. For tradespeople, understanding which Parts apply to which work is the difference between delivering a compliant job and creating a liability.

The regulations are enforced by Building Control Bodies (BCBs) — either the Local Authority Building Control (LABC) or an Approved Inspector (now called a Registered Building Inspector under the Building Safety Act 2022). The contractor's obligation is to notify where required and to build to the correct standard regardless of whether formal approval is in place.

One of the most common misconceptions is that because a job is small, it does not need to comply. Regulations do not have a size threshold for compliance — they have a threshold for notification. You must comply even if you do not need to notify. Getting that wrong leaves you and your customer exposed.

Key Facts

• Legal basis: Building Act 1984 and the Building Regulations 2010 (SI 2010/2214) and subsequent amendments
• England and Wales: Most Approved Documents apply; some Wales-specific amendments apply
• Scotland: Covered by the Building (Scotland) Regulations 2004 — different standards and documents
• Northern Ireland: Building Regulations (Northern Ireland) 2012 — separate system
• Approved Documents: Non-statutory guidance on meeting the regulations; they are not regulations themselves — alternative approaches can be used if they meet the functional requirement
• Notification threshold: "Building work" as defined in Regulation 3 must be notified — this includes new building, extensions, material alterations, installation of controlled services/fittings (boilers, electrical), changes of use
• Exemptions: Certain works are exempt — see Schedule 2 of the Building Regulations 2010; includes detached garages under 30m², conservatories under certain conditions, some porches
• Competent Person Schemes: Allow self-certification without a full BC application — see competent person
• Building Safety Act 2022: Introduces new requirements for higher-risk buildings (HRBs) — 18m+ or 7+ storeys — most domestic work is not in scope
• Fee: LA Building Control charges plan check and inspection fees; fees vary by Local Authority
• Completion certificate: Must be obtained on completion — essential for property conveyancing

Quick Reference Table

Detailed Guidance

What is "Building Work"?

Regulation 3 defines building work as:

• New building or structure
• Extension of a building
• Material alteration — work that would have a negative impact on compliance if the regulations applied to the whole building; e.g. removing a loadbearing wall, altering a drainage system
• Installation of controlled services — heating systems, ventilation, electrical wiring, sanitary fittings, unvented hot water cylinders
• Work in connection with a material change of use

What is NOT building work:

• Maintenance and repair (like-for-like replacement)
• Normal decoration
• Routine servicing of controlled services

Part A — Structure

Part A applies to:

• Extensions of any size
• Loft conversions (structural changes to roof)
• Removal of loadbearing walls or structural elements
• New outbuildings exceeding 30m² or on a boundary

Key requirement: Structural work must be designed to Eurocode or accepted UK structural engineering standards. For straightforward extensions and loft conversions, a structural engineer's calculations are usually required.

Does NOT apply to: Non-structural internal alterations (e.g. adding a non-loadbearing partition), routine maintenance.

Part B — Fire Safety

Part B is frequently triggered without contractors realising. Key triggers:

• Loft conversion: The escape route through the dwelling (the staircase) must be upgraded — fire doors to habitable rooms on the staircase, sometimes smoke alarms and mains-wired detection
• HMO / change of use: Converting to a house in multiple occupation requires compartmentation, fire doors, and detection per the LHA's requirements (often governed by Housing Act 2004 rather than or in addition to Part B)
• New habitable room above ground floor: Means of escape from the room required

Does NOT apply to: Normal internal decoration, fitting kitchens or bathrooms without structural change, maintenance.

Part L — Energy Efficiency

Part L is frequently triggered and frequently ignored:

• Any window replacement: New windows must meet minimum U-value (1.4 W/m²K for replacement windows in existing dwellings — the installer must self-certify or use a FENSA/CERTASS registered company)
• New boiler installation: Must comply with minimum efficiency standards; condensing boiler required except in limited exemption cases
• Extension: Must achieve the required fabric performance (walls, roof, floor, windows to specified U-values)
• Conservatories with heating: Must meet insulation standards

Notifiable under Part L: Window replacement, new boilers — both have competent person scheme routes.

Part G — Sanitation and Hot Water

Part G is triggered by:

• Any new unvented hot water cylinder — must be installed by a Part G competent person (usually G3-certified)
• New bathrooms or toilets in buildings where no existing facility serves that area
• New boiler installation (overlaps with Part J and Part L)

Part P — Electrical

Part P applies to all electrical work in dwellings. Notifiable work includes:

• New circuits
• Consumer unit replacement
• Any work in kitchens, bathrooms, or outdoors
• See part p notifications for full detail

Part J — Combustion Appliances

Part J applies to:

• Any new boiler or gas fire (also subject to Gas Safety (Installation and Use) Regulations — must be done by Gas Safe Registered engineer)
• Wood-burning stoves and solid fuel appliances — HETAS registration provides self-certification route
• Oil-fired appliances — OFTEC registration provides self-certification route
• Flue lining and flue alterations

When Do You Need Full Building Control Application?

A full Building Control application (Full Plans or Building Notice) is required when:

• The work is "building work" and no competent person scheme covers the trade/work type
• The work is an extension or loft conversion
• The work involves structural alteration
• The work involves drainage alteration

A Building Notice is simpler (no plans required) but carries risk — work may be inspected and found non-compliant. Full Plans applications are recommended for extensions and loft conversions.

Competent Person Schemes — Avoid the Application

For many common trade installations, a competent person scheme allows self-certification:

• Gas: Gas Safe Register (mandatory, not a competent person scheme in the traditional sense — legal requirement)
• Electrical: NICEIC, NAPIT, ELECSA
• Windows/doors: FENSA, CERTASS
• Boilers/heating: Gas Safe (Part J), HETAS (solid fuel), OFTEC (oil)
• Microgeneration: MCS (solar PV, heat pumps)

See competent person for full scheme list.

Frequently Asked Questions

If I do building work without notification, what happens?

Without a completion certificate, the customer cannot prove compliance at conveyancing — this typically causes complications when selling. The Local Authority has powers to require removal or alteration of non-compliant work under Section 36 of the Building Act 1984. Regularisation applications can sometimes retrospectively certify work, but this requires proving the work meets current standards (or standards at time of construction), often involving opening up. The contractor may also face civil liability if the non-compliant work causes harm.

Do small extensions under a certain size need Building Regulations?

No size exemption applies — all extensions require Building Regulations compliance and notification (unlike planning permission, which has a permitted development limit). A single-storey rear extension of 1m² still requires Building Control.

Does replacing a bathroom need Building Regulations?

Like-for-like replacement of sanitary fittings does not require a Building Regulations application. If you are moving drainage, adding a new bathroom, or installing an unvented hot water cylinder, those elements are notifiable. Electrical work in a bathroom is notifiable under Part P.

What is the difference between planning permission and Building Regulations?

Planning permission is about whether a building or use is acceptable in planning policy terms — scale, appearance, impact on neighbours, use. Building Regulations are about whether the construction meets minimum technical standards for safety, health, and efficiency. You can have planning permission but still need to comply with Building Regulations. Most extensions need both.

What are the differences between England, Wales, and Scotland?

England and Wales use the Building Regulations 2010 and Approved Documents. Wales has introduced some divergence, particularly on energy efficiency (Part L) and accessibility (Part M). Scotland uses a completely separate system — the Building (Scotland) Regulations 2004 with Technical Handbooks (Domestic and Non-Domestic). If you work in Scotland, do not rely on England and Wales guidance.

Regulations & Standards

• Building Regulations 2010 (SI 2010/2214) — primary statutory instrument; regularly amended

• Building Act 1984 — legislative basis for building control in England and Wales

• Building Safety Act 2022 — new framework for higher-risk buildings; introduces new duty holders

• The Building (Approved Inspectors etc.) Regulations 2010 — approved inspector framework (transitioning under BSA 2022)

• Building Regulations Approved Documents — GOV.UK — Official Approved Documents (A–S)

• Planning Portal — Building Regulations — Plain English guidance on when regulations apply

• LABC — Local Authority Building Control — Guidance for contractors on LA building control

• part p notifications — Electrical notification detail

• part l energy — Energy efficiency requirements

• part b fire — Fire safety requirements

• part m access — Accessibility requirements

• building control — How to make a Building Control application

• competent person — Self-certification schemes