Building Regulations in London: What Every Homeowner Needs to Know

Building Regulations are made under the Building Act 1984 and set out technical standards for construction through a series of Approved Documents (Parts A through R). The main Parts relevant to residential projects in London are: Part A — Structure (foundations, walls, beams, floors, roofs); Part B — Fire Safety (means of escape, fire resistance of elements, spread of fire); Part C — Site Preparation and Resistance to Contaminants and Moisture (damp-proofing, drainage, ground conditions); Part E — Resistance to the Passage of Sound (sound insulation between dwellings and between a dwelling and a noise source); Part F — Ventilation (adequate ventilation for habitable rooms, kitchens, bathrooms, and sanitary accommodation); Part G — Sanitation, Hot Water Safety and Water Efficiency (installation of sanitary fittings, hot water systems, water fittings); Part H — Drainage and Waste Disposal (drainage systems); Part K — Protection from Falling, Collision and Impact (staircase design, guarding, barriers); Part L — Conservation of Fuel and Power (thermal performance, insulation, boiler efficiency); Part M — Access to and Use of Buildings (accessibility and adaptable design); Part P — Electrical Safety (electrical installations); Part Q — Security (window and door security specifications for new dwellings); and Part R — High Speed Electronic Communications Infrastructure (broadband provision in new buildings).

Building Regulations apply to most structural work, service installations, and changes of use in buildings. In the residential context, Building Regulations approval is required for: any extension to a dwelling (single-storey, two-storey, rear, side); any loft conversion (including those permitted under Permitted Development); any basement conversion; structural alterations (removing load-bearing walls, installing beams); installation of new bathrooms, kitchens (involving drainage or ventilation changes); installation of new electrical circuits (Part P notifiable work); installation of central heating and boiler systems (Part J and Part L); installation of replacement windows (Part L and Part Q, unless self-certified by a FENSA or Certass registered installer); new drainage connections; and conversion of a house into flats. Building Regulations do not apply to: ordinary maintenance and repair; replacing like-for-like elements with the same specification (such as replacing a broken tile); most internal redecoration; and some minor alterations that do not affect the structure or services.

There are two routes to Building Regulations approval: Full Plans: you submit detailed technical drawings and specifications to Building Control before starting work. Building Control checks the plans, may request revisions, and issues an approval (or conditional approval). This route provides certainty before starting and is recommended for complex or large projects. Building Notice: you notify Building Control of the intended works but do not submit detailed plans in advance. Building Control inspectors visit during construction and check the works on site. This route is faster to start but provides less certainty — if Building Control finds a problem during inspection, remedial works may be required. In London, Building Control can be carried out by: the local authority Building Control department; or an Approved Inspector (a privately registered independent inspector). Both routes are equally valid. For most residential projects in London, the local authority Building Control is commonly used — fees and processes vary by borough.

During construction, the building control inspector visits at key stages to check that the works comply with the Regulations. Typical inspection stages for an extension: commencement (to check the site conditions and confirm the works have started); foundation excavation (to check the excavation depth and ground conditions before concrete is poured); damp proof course (to check the DPC position and specification); oversite (before the ground floor slab is poured); frame and first-fix services (to check the structural frame, insulation, fire-stopping, and first-fix plumbing and electrics before these are concealed); roof structure (to check the roof structure if applicable); and completion (to check all finished works and issue a Completion Certificate). It is important to give Building Control adequate notice before each inspection stage and to ensure critical elements are not covered up before inspection. For example, concrete must not be poured over the foundation excavation until the excavation depth has been checked by Building Control. A Completion Certificate is issued by Building Control after the final inspection when all requirements are met. This certificate is a key document for property sale — solicitors ask for it and it confirms the works were carried out in compliance with the Regulations.

Part L (Conservation of Fuel and Power) of the Building Regulations sets increasingly demanding energy efficiency standards for new buildings and extensions. For extensions to dwellings, Part L requires that: the new extension fabric (walls, floor, roof, windows) meets minimum U-value standards (e.g., external walls 0.18 W/m2K, roofs 0.13 W/m2K, floors 0.18 W/m2K, windows 1.4 W/m2K); the extension does not make the overall carbon performance of the dwelling significantly worse; fixed building services (lighting, heating) in the extension meet minimum efficiency standards. For extensions smaller than 30m2 (the most common case in London), the requirements are less onerous than for larger extensions and new dwellings. London has also adopted an optional higher standard — the London Plan Policy SI2 requires new development in London (including extensions over certain thresholds) to meet a higher energy performance target than the national minimum. Your borough's planning department can advise on whether this applies to your project.