Building Regulations in London: A Homeowner's Complete Guide

Planning permission and Building Regulations are often confused, but they are completely separate processes with different purposes. This guide focuses on Building Regulations — what they cover, when you need approval, and how to navigate the process in London.

What Are Building Regulations?

Building Regulations set minimum technical standards for construction work in England. They exist to protect the health and safety of building occupants and to ensure buildings are energy-efficient and accessible.

They are not about whether something can be built — that is planning permission. They are about how it must be built.

Who Enforces Building Regulations?

Building Regulations approval is provided by one of two types of body:

Local Authority Building Control (LABC): The council's building control department. Fees are set by the council and are generally modest. Applications are made directly to the council.

Approved Inspector (AI) / Registered Building Inspector (RBI): Private sector inspectors approved to carry out the same function. Fees are set commercially. For London residential projects, both routes are equally valid.

From April 2024, the building safety reforms introduced under the Building Safety Act 2022 also created the Building Safety Regulator (BSR) for higher-risk buildings (HRBs) — primarily residential buildings of 7 storeys or 18m or more. Most domestic projects are not affected by HRB requirements.

Which Projects Require Approval?

Building Regulations approval is required for a wide range of work, including:

• Extensions (all sizes)
• Loft conversions (almost all)
• Garage conversions (creating habitable space)
• Structural alterations (wall removals, beam insertions, underpinning)
• New or replacement windows and doors (in most circumstances — energy performance)
• Heating and hot water system installations
• Electrical work (certain types — see Part P)
• Drainage work
• New bathrooms or kitchens where drainage is being extended

Some minor works are exempt, including small single-storey outbuildings up to 15m² and certain repair and maintenance work. But when in doubt, check — the consequences of proceeding without approval when it was required are significant.

The Application Process

There are two types of Building Regulations application:

Full Plans Application You submit detailed drawings and specifications before work begins. Building Control reviews and formally approves them. This is the recommended route for larger projects because it gives you written confirmation that your proposed design complies before you invest in construction.

Building Notice A simpler notice to Building Control that work is about to start. No plans are submitted for approval — instead, the inspector visits the site at key stages. This is faster to initiate but carries more risk if issues emerge on site, because there is no pre-approved design to fall back on.

For loft conversions, extensions, and structural alterations, RCB recommends the Full Plans route to protect your project and provide clarity at each stage.

Inspections

Once work starts, Building Control will carry out inspections at key stages. Typical inspection stages include:

• Commencement: After work begins
• Foundation/excavation: Before concrete is poured
• DPC (damp-proof course): After the damp-proof course is laid
• Concrete oversite: Before floor slab is poured
• Drains: Before backfilling
• Frame/structural steel: After key structural elements are in place
• Insulation: Before it is covered up
• Final inspection: After completion

Missing a required inspection can mean being asked to open up completed work for inspection — an expensive and disruptive outcome. RCB's project management includes coordinating all inspection stages so nothing is missed.

The Completion Certificate

When all inspections are passed and the work is complete, Building Control issues a Completion Certificate. This is a critical document.

Without it:

• Your insurer may not cover the completed work
• Your conveyancer will flag the absence when you sell
• The buyer's surveyor will identify it as a defect
• Mortgage lenders may refuse to lend on the property

Completion Certificates should be kept with your property documents permanently.

Regularisation: What if Work Was Done Without Approval?

If you buy a property or discover that previous work was done without Building Regulations approval, a Regularisation Certificate can sometimes be obtained retrospectively. You apply to the council, they inspect (which may involve opening up finished areas), and if the work complies with the regulations that applied at the time it was carried out, a Regularisation Certificate is issued.

This is only available via Local Authority Building Control — not Approved Inspectors.

Permitted Development and Building Regulations Are Separate

A common misunderstanding: if your extension is under Permitted Development (no planning permission needed), Building Regulations still apply. PD rights relate to planning law; Building Regulations relate to construction standards. You need to satisfy both.

Energy Efficiency Requirements

Part L of the Building Regulations (Conservation of Fuel and Power) sets energy performance standards. For extensions and conversions, the new floor area must meet minimum U-value standards for walls, roofs, floors, windows, and doors. Failure to comply can mean expensive remediation or being unable to sell the property.

On larger projects, a SAP (Standard Assessment Procedure) or SBEM calculation may be required to demonstrate compliance.

RCB Design & Build

RCB manages the full Building Regulations process on all projects — application preparation, submission, and inspection coordination. Our approach ensures the Completion Certificate is issued promptly so your project is fully compliant and ready for sale or refinancing. Contact us to discuss your project.