Building Regulations for House Extensions

Introduction to Building Regulations for House Extensions

House extensions have become increasingly popular across the UK as homeowners seek to create more space and enhance the functionality of their properties. Whether it’s to accommodate a growing family, create a home office, or add extra living space, extensions offer a flexible solution to meet diverse needs. In this post, we will explore the requirements of the Building Regulations when it comes to house extensions.

Building Regulations serve as a set of essential standards that ensure buildings are safe, healthy, and sustainable for occupants. For house extension projects, adherence to the regulations is mandatory, not only for the structural integrity and safety of the extension but also for legal compliance. While obtaining planning permission may be the initial focus, Building Regulations approval is equally essential and should be considered early on to avoid design changes later.

01 Detached house extension

Understanding Building Regulations

The building regulations comprise of a number of Approved Documents each detailing the standards required to achieve compliance.

The documents are as follows:

Approved Document A – Structure
Approved Document B – Fire Safety
Approved Document C – Site Preparation and Resistance to Contaminants and Moisture
Approved Document D – Toxic Substances
Approved Document E – Resistance to Sound
Approved Document F – Ventilation
Approved Document G – Sanitation, Hot Water Safety and Water Efficiency
Approved Document H – Drainage and Waste Disposal
Approved Document J – Combustion Appliances and Fuel Storage Systems
Approved Document K – Protection from Falling, Collision and Impact
Approved Document L – Conservation of Fuel and Power
Approved Document M – Access to and use of Buildings
Approved Document O – Overheating
Approved Document P – Electrical Safety
Approved Document Q – Security in Dwellings
Approved Document R – Infrastructure for Electronic Communications
Approved Document S – Infrastructure for Charging Electric Vehicles
Approved Document 7 – Material and Workmanship

All of the documents are available from the Gov website, where they can be viewed and downloaded in PDF format. The documents do get updated, so it is recommended you check back regularly to ensure you are working on the most up to date version. You can also subscribe to alerts from to ensure you don’t miss any important updates.

Many of the documents will need to be referenced and considered for an extension project. In addition to the Approved Documents, it may also be necessary to refer to other guidance such as the British Standards.

All house extensions are different, and we encourage you to study the regulations for every project to ensure compliance.

02 Interior house extension living area

Scope of Building Regulations for House Extensions

It is important to understand the scope of the Building Regulations for house extensions, so during design you know the elements that are referenced in the regs and can ensure compliance from an early stage. Unlike planning permission, which focuses primarily on the visual impact and land use considerations of a proposed development, Building Regulations delve into the details of the construction process, ensuring that the resulting structure is safe, healthy, and sustainable for its occupants.

One of the key points to note is that almost all house extensions require approval under Building Regulations, regardless of whether planning permission is needed. This means that even if your extension falls within the permitted development rights outlined by your local planning authority, you still need to comply with the Building Regulations to ensure that your project meets the required standards.

When You Need Approval for House Extension Projects

It is necessary to get Building Regulations approval before you carry out any new structural work or alterations to an existing property.

In addition, you might need approval if you plan to:

  • replace fuse boxes or connected electrics
  • install a bathroom that will involve plumbing
  • change electrics near a bath or shower
  • replace windows and doors
  • replace roof coverings on pitched or flat roofs
  • install or replace a heating system
  • add extra radiators to a heating system
  • make changes to drainage
  • install new cavity wall insulation
  • removing a chimney breast

Some of the above alterations can be carried out by someone registered with a competent person scheme, meaning that the person is able to self certify their work. In this case the work will be carried out to the correct standards and you will not be required to apply for building regulation approval.

However, the likelihood is that as a designer on an extension project, structural changes will be required therefore it will be necessary to seek Building Regulation approval.

03 Interior house extension

Key Requirements for House Extension Projects

There are several key requirements outlined in the Building Regulations that must be adhered to when working on a house extension project. These requirements cover various aspects of the extension’s construction, ensuring that it meets essential standards for safety, health, and sustainability. Let’s explore these key requirements in more detail:

Structural Stability

Building Regulations stipulate that house extensions must be structurally sound to ensure the safety of occupants. This includes considerations such as the adequacy of foundations, the strength of load-bearing walls, and the stability of roof structures.

Refer to Approved Document A – Structure and Approved Document C – Site Preparation and Resistance to Contaminants and Moisture

Fire Safety

Fire safety is a critical aspect of Building Regulations for house extensions. Requirements include provisions for escape routes, the use of fire-resistant materials, and the installation of smoke alarms.

Refer to Approved Document B – Fire Safety

Energy Efficiency

With increasing emphasis on sustainability and energy efficiency, Building Regulations place significant importance on the thermal performance of house extensions. This includes requirements for adequate insulation, energy-efficient windows and doors, and efficient heating systems.

Refer to Approved Document Part L – Conservation of Fuel and Power

Ventilation and Air Quality

Good indoor air quality is essential for the health and comfort of occupants. Building Regulations set out requirements for ventilation provision, ensuring that fresh air is supplied to habitable rooms while excess moisture and pollutants are removed. Ventilation requirements are particularly complex for house extensions, especially when upgrading and improving the existing house along with the new extension structure. Be sure to check the regulations.

Refer to Approved Document Part F – Ventilation


Building Regulations also address accessibility considerations, however unfortunately these are predominantly optional for house extensions. We would always try to ensure we can provide suitable accessibility features such as increased door widths, ramp gradients, accessible bathroom facilities and more. This allows not only for future proofing for the existing occupants, but also provides optionality for future occupants of the home.

Refer to Approved Documents Part K – Protection from Falling, Collision and Impact and Part M – Access to and Use of Buildings

Other Requirements

The list doesn’t stop there. Work carried out to kitchens or sanitary facilities will need to comply with the regulations, refer to Approved Document F – Ventilation, Approved Document G – Sanitation, Hot Water Safety and Water Efficiency and Approved Document H – Drainage and Waste Disposal. In addition, the installation of a wood burning stove for example, will also need to be designed and installed according to Part J – Combustion Appliances and Fuel Storage Systems.

04 Kitchen interior extension


The requirements of the Building Regulations range far and wide in all construction projects, with house extensions being no exception. Building Regulations not only protect occupants but also contribute to the overall quality of the built environment, ensuring that our homes are resilient, efficient, and inclusive.

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Written by Emma Walshaw, Architectural Technologist and founder of First In Architecture and Detail Library. Emma has written a number of books about construction and architectural detailing.

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