Building Regulations in England: What They Are, Which Works Need Approval, and How to Get It

Building Regulations in England are implemented through a set of Approved Documents, each providing technical guidance on how the functional requirements of the Building Regulations can be met. The main Approved Documents relevant to residential extension and renovation work are:

Approved Document A — Structure: The structural performance requirements of the building — foundations, walls, floors, roofs, and their ability to support imposed loads without failure. For an extension, Part A is satisfied by the structural engineer's design and the Building Control inspector's confirmation that the structure has been built in accordance with the approved design.

Approved Document B — Fire Safety: The requirements for means of escape in case of fire, internal fire spread, external fire spread, and access for firefighting appliances. For residential extensions, the most significant Part B requirements relate to: means of escape from any new habitable room; smoke detection on all floors; fire doors where required; and (for extensions to buildings with more than one dwelling) fire compartmentation between units.

Approved Document C — Resistance to Contaminants and Moisture: The requirements for damp-proofing, resistance to ground moisture, and resistance to contaminants in the ground. For an extension, Part C is satisfied by providing a damp-proof course in the cavity wall, a damp-proof membrane beneath the floor slab, and cavity drainage or waterproofing where the extension includes any below-ground spaces.

Approved Document F — Ventilation: The requirements for providing adequate ventilation to all habitable rooms, kitchens, bathrooms, and utility rooms. For a new extension, background ventilation (trickle vents in windows), rapid ventilation (openable window area equal to at least 1/20th of the floor area), and (for kitchens) extract ventilation to outside are typically required.

Approved Document L — Conservation of Fuel and Power: The thermal performance requirements for new and extended buildings. Part L specifies maximum U-values for new walls, floors, and roofs in extensions and new buildings, and requires that the overall thermal performance of the dwelling is not significantly worsened by the extension work. From 2022, Part L 2021 applies — requiring improved U-values compared with the previous 2016 edition.

Approved Document P — Electrical Safety: All new electrical installation work must comply with BS 7671 (the IET Wiring Regulations, 18th edition) and must be notified to and certified by a Part P registered electrician (or inspected and certified by Building Control).

The Building Regulations 2010, Schedule 2, defines exempt works. Everything not in Schedule 2 requires Building Regulations approval. For a London homeowner, the key categories are:

Works that almost always require Building Regulations approval: Extensions (any size — even a small conservatory connected to the house by internal-quality doors). Loft conversions (converting non-habitable attic space to habitable rooms). Basement conversions (converting cellar space to habitable rooms). Structural alterations (removing or forming openings in load-bearing walls, inserting steel beams, underpinning). New or replaced drainage (any new drain runs, new connection to a sewer, installation of new soil and waste pipes). New boiler or central heating system installation (Part J — Combustion Appliances; the installation must be notified and certified by a Gas Safe registered engineer). New electrical circuits (Part P — any new circuit from the consumer unit in a notifiable location). New or replacement windows (FENSA or CERTASS registration is typically used to self-certify replacement windows as an alternative to a Building Control application). Garage conversion to habitable room (change of use to habitable accommodation). Reroofing (if significant — where the roof structure is altered or more than 25% of the roof covering is replaced).

Works that are generally exempt: Like-for-like repair and maintenance (replacing roof tiles on a like-for-like basis, re-pointing, internal decoration, replacing a like-for-like window in the same opening). Small detached outbuildings under 15m² with no foul drainage (garden sheds, small garden offices where there is no sleeping accommodation). Conservatories under 30m² with a thermally separated connection to the house and safety glazing. Small porches under 30m² with no foul drainage and not within 1 metre of a relevant boundary.

What "self-certification" means: Some trades can self-certify their work without a Building Control application, under Competent Persons Schemes. Gas Safe engineers self-certify boiler and central heating installation (the certification is issued directly without a Building Control inspection). FENSA-registered window installers self-certify replacement window installation. An ELECSA or NICEIC registered electrician can self-certify Part P notifiable electrical work.

Full Plans Application: The Full Plans route involves submitting detailed technical drawings and a specification to the Building Control body (LABC or Approved Inspector) before work commences. The Building Control inspector reviews the drawings and specification and either issues a conditional or full plan approval, or raises queries for the applicant to address.

How it works: Submit the Full Plans application with: site plan, existing and proposed floor plans and sections at a scale sufficient to show all Building Regulations compliance details; structural drawings and calculations (from the structural engineer); drainage design; specification of insulation types and thicknesses with calculated U-values; fire safety strategy. The Building Control body reviews the submission (typically within 5 weeks for a standard residential application). A conditional approval or full approval is issued, or queries are raised. The builder commences work, notifying the Building Control body at each key inspection stage. The Building Control inspector visits at each key stage and records the inspection. On completion, a Final Certificate (for an Approved Inspector) or a Completion Certificate (for LABC) is issued.

Advantages of Full Plans: The plan approval document confirms that the proposed design will comply before the work is built — reducing the risk of costly remediation if the inspector identifies non-compliance in the completed work. Required by most mortgage lenders and expected in property sale conveyancing. Preferred by solicitors and conveyancers because the paper trail (application, approval, inspection records, completion certificate) is complete.

Building Notice: The Building Notice route involves a simpler application submitted 48 hours before work commences, with no drawings or specifications submitted in advance. The Building Control inspector assesses compliance during and after construction rather than in advance.

How it works: Submit the Building Notice form with a basic plan showing the site and the nature of the proposed work. Work commences after 48 hours. The Building Control inspector inspects at key stages. If the inspector identifies non-compliance, they can require opening up and remediation — at the applicant's cost — before approving the work. A completion certificate is issued on completion of the work (in London, LABC completion certificates are now generally accepted by conveyancers).

Advantages of Building Notice: Simpler and faster to initiate (no full design pack required before starting). May be appropriate for straightforward, simple works where the compliance strategy is clear.

When to use Full Plans: For any significant structural alteration, extension, loft conversion, basement conversion, or new drainage works — Full Plans is strongly recommended. The additional upfront effort of preparing the full technical design package (structural drawings, Part L calculations, drainage design) pays dividends in avoiding compliance disputes at the end of the project.

Building Regulations inspections take place at key stages of the construction, when specific elements are about to be covered up or completed. The Building Control inspector must be given sufficient notice before each stage inspection — typically 24 hours for most stages.

Standard key stages for a single-storey rear extension:

1. Commencement notification: The builder (or applicant) must notify the Building Control body that work has commenced, within 48 hours of starting. No site inspection is required at this stage — it is simply a notification.

2. Foundation inspection: Before the concrete is poured. The inspector checks that the excavation is at the correct depth, that the soil conditions are appropriate for the specified foundation type, and (in the presence of trees or made ground) that the conditions match the structural engineer's assumptions.

3. Oversite and DPC inspection: When the oversite (the sub-base material below the floor slab) is prepared and the damp-proof membrane (DPM) is laid but before the concrete floor slab is poured. The inspector checks the DPM continuity, the edge insulation upstand detail, and the thickness and specification of the sub-base.

4. Drainage inspection: Before any drainage is covered (backfilled). The inspector checks the pipe gradients (minimum 1:40 for 100mm diameter pipes), the pipe specification, the jointing, the inspection chamber positions, and the connection to the existing drainage.

5. Frame/walls/structural steel inspection: At a suitable stage when the structural elements are erected but before any wall finishes are applied. The inspector checks cavity wall ties, cavity width, structural steel installation (beam size, padstone bearing, and temporary propping removal), and any fire-stopping required at party wall penetrations.

6. Pre-plasterboard inspection: Before wall and ceiling insulation and plasterboard are fixed. The inspector checks the first-fix electrical installation, the first-fix plumbing and pipework, the wall and ceiling insulation specification and continuity, fire-stopping at penetrations through compartment walls and floors, and any structural elements visible within the stud wall or partition construction.

7. Completion inspection: When the work is substantially complete. The inspector checks all visible elements for compliance — ventilation (trickle vents, extract fans), smoke detection, staircase dimensions and guarding, glazing safety marking, external drainage, and the overall compliance of the completed works with the approved design (for a Full Plans application) or with the Building Regulations requirements (for a Building Notice).

The Completion Certificate: On satisfactory completion of the key stage inspections and the final inspection, the Building Control body issues a Completion Certificate (LABC) or a Final Certificate (Approved Inspector). This certificate is a legal document confirming that the work has been inspected and found to comply with the Building Regulations.

The Completion Certificate must be retained by the homeowner — it will be required by: Mortgage lenders if the property is to be remortgaged or sold. Solicitors acting in the conveyance of the property. Any future purchaser's surveyor or solicitor when inspecting the property's compliance history.

Carrying out notifiable building work without obtaining Building Regulations approval (or without a completion certificate) creates several serious problems:

Property sale difficulties: When you sell the property, your solicitor will disclose the building work. The buyer's solicitor will ask for the Building Regulations completion certificate. If there is no certificate (because the work was done without approval), the buyer may: Require you to obtain a Regularisation Certificate from LABC (an application to retrospectively approve work already carried out) — which may require opening up the completed work for inspection. Require you to take out Indemnity Insurance against the risk that the local authority issues an Enforcement Notice. Reduce their offer to reflect the uncertainty about compliance. In extreme cases, refuse to proceed without evidence of compliance.

Enforcement: Under the Building Act 1984, the local authority can issue an Enforcement Notice requiring the alteration or removal of non-compliant building work for a period of 12 months after completion. For work completed after 1 April 2023, the Building Safety Act 2022 has extended enforcement powers in specific circumstances. For older unauthorised work (more than 12 months old), enforcement powers are more limited — but the property sale implications remain.

Regularisation: A Regularisation Certificate can be applied for from LABC (not available from Approved Inspectors) for unauthorised work. The application requires the applicant to expose previously covered elements for inspection (opening walls, lifting floors) so that the Building Control inspector can assess compliance. If the work is found to comply, a Regularisation Certificate is issued. If it is found not to comply, remediation works must be carried out before the certificate is issued. The Regularisation Certificate is recognised by most mortgage lenders and conveyancers, though it does not carry the same weight as a standard Completion Certificate.

Insurance: Some building insurance policies exclude claims arising from defects in building work carried out without Building Regulations approval. Ensuring that all notifiable building work is properly approved and certified protects the homeowner's insurance position as well as their legal compliance position.