What Building Regulations Do I Need for an Extension?

// House Extensions

What Building Regulations Do I Need For An Extension?

“Greg “Home


A question often googled is what building regulations do I need for a home extension? Jeffery and Wilkes are London’s leading house extension specialists
If you are looking to carry out extension works to your property, it is likely that building regulations approval is required.

Building regulations make sure that the completed work is performing well and is safe to use.

If you do not seek building regulations approval, not only do problems arise when it comes to selling the property, but you also face the risk of prosecution and enforcement from the local authority.

In this article, we are going to answer the following key points

• What are building regulations?
• Why were building regulations introduced?
• Why building regulations are important
• What are the building regulations for a home extension?
• How the process works
• What happens if you DO NOT seek building regulations approval

What are Building Regulations and Where Did They Come From?

The Building Act 1984 allows the creation, issue and enforcement of what is known as building regulations. It only applies to England and Wales. From the building act 1984, the building regulations 2010 were created. The regulations contained in the Building Regulations 2010 are simple and wide-ranged, so clarity is provided by way of Approved Documents. The approved documents are lettered for different topics of work such as Part A for Structure and Part B for Fire Safety.
The building regulations play an important part in the design and build of a project. The standards set out in the approved documents must be met such as the size of the roof joists and the thickness of the external walls.
The requirements of the building regulations are the same for all types of projects, so the insulation needed for a flat roof of an extension will be the same as for the flat roof of a dormer in a loft conversion.
The process of inspection and approval

Before carrying out building works that require building regulations approval, you must appoint a building control body; either the local authority, or an approved inspector.
For small projects such as an extension, usually a building notice suffices. This allows works to start on site in as little as 48 hours if you appoint the local authority, or 5 days if you appoint an approved inspector.
For larger projects such as new builds, it is likely that a full plans submission is required, which can take the local authority 5-8 weeks to turn around, compared to only 5-10 days by approved inspectors.
The building inspector will inspect different stages of the works where breaches to the building regulations are most likely to occur. Common examples include excavation for foundations, damp proof course, drainage and insulation.

What Regulations apply to my Extension Work?

An extension will include many different elements and sub elements; however, the building regulations will generally concern the following areas:
• Roof
• Walls (internal & external)
• Doors, Windows & Rooflights
• Electrical works
• Drainage
• Kitchens & Bathrooms


Generally, the new roof to the extension must be weather resistant, sufficiently insulated, ventilated and structurally sound.
The two most common types of roofs for an extension is flat or pitched. A flat roof is usually covered in felt and has only a slight fall to allow water runoff. A pitched roof on the other hand is covered with tiles. The roof must be watertight and able to resist all types of weather. If the roof is close to any neighbouring properties, it will be resistant to fire spread too.
Insulation is used to minimise heat loss or heat gain into the extension. The insulation used as part of the roof system must achieve the minimum as required in the approved documents. There are two types of roof systems; one is a warm roof and the other is a cold roof. A warm roof system is where the insulation sits on top of the roof joists. A cold roof system is where the insulation is place between the roof joists.
Ventilation is required to a cold roof to allow air to travel between the insulation and the covering above.
Roof joists are the main structural elements of a roof system. Roof joists come in different sizes and can be placed at certain distances from one another, depending on the loadings and spans. The structural engineer will specify the size of roof joists and their spacings, however the requirements are also available in Trada’s span tables which are referred to in the approved documents.


Generally, the external walls are checked for thermal efficiency, weather resistance and structural stability.
External walls can either be solid or cavity. Solid walls were primarily built in previous years; however, cavity walls are the most common form of external wall construction nowadays. Solid walls consist of one skin of brickwork, whereas a cavity wall has two skins of brickwork, separated by air and/or insulation. It’s much more difficult to achieve the current required u-values with solid walls, therefore cavity walls are the preferred choice of construction for new extensions.
External walls require damp proofing to prevent water and dampness from entering the inside of the extension. A damp-proof course is placed at least 150mm above the external ground level to prevent damp rising through the brickwork and into the building. This damp-proof course is tied in with a damp-proof membrane which lines the floor of the build. This damp-proof membrane forms a barrier between the inside of the building and the damp from the earth beneath.
Most extension work involve a structural opening to form an open plan area, usually to the rear or side wall of the main house. This opening is supported by a steel beam which loads on the remaining brickwork either side. Building control will check that the works are carried out in accordance with the structural engineer’s design.

Doors, Windows & Rooflights

Lintels are installed above doors and windows to support the loading above. The lintels must be in accordance with the approved documents and the structural engineers design.
All glazing must achieve the minimum u-values as required by the approved documents. Manufacturers ensure their products achieve these ratings and provide data sheets to prove this.
Openings need to be created for windows, doors and rooflights. These openings need to be watertight, airtight and insulated.

Electrical Works

If an electrician is used who is registered with a competent person scheme, they can self-certify the work without the need of building control sign off. If the installer is not registered with a competent person scheme, notifiable works need to be inspected and signed off by building control. For extension works, a complete re-wire of the property or alterations to existing circuits are likely to occur; works such as these are classed as notifiable.


Approved document H concerns drainage and waste disposal. The builders will need to make specific regard to this document when carrying out works for the drainage and waste disposal.
Drainage is separated into two categories: Foul drainage and surface water drainage.
Foul drainage carries the wastewater from areas such as the toilet, sinks, dishwasher and washing machine. Pipework above ground us known as sanitary pipework and the pipework below ground level is known as foul drainage and foul sewers. This wastewater is usually disposed of via the mains sewers serving the property.
Surface water drainage collects the water from the rain and snow which falls on roof surfaces. The roof drainage usually includes guttering and downpipes; the below ground pipework is known as surface water drains and sewers. A soakaway is sometimes constructed in the garden to alleviate the stress placed on the sewer system. A large hole is dug into the earth several meters away from the building with the surface water drainage running into it. Alternatively, this water runs into the sewers, along with the foul drainage.
If you are building over or within 3 meters of a public sewer, a written agreement with the sewage undertaker is required. Detailed drawings are usually required to support this build over application. If building over or near a public sewer, there is the risk of it becoming damaged and collapsing. This affects all properties which are served by this sewer, hence the need for this written agreement.
A surprisingly big factor bearing on the design of an extension is the drainage. If you wanted to build 3 meters outwards, however the public sewer also runs at 3m from your property, you may have to compromise by setting the extension inwards slightly, or re-designing the foundations so that they can bridge over to satisfy building control and the sewage undertaker.

Kitchens & Bathrooms

There isn’t much in terms of building regulations when it comes to kitchens and bathrooms. The biggest requirement is adequate ventilation under approved document F.

What if I don’t seek building regulations approval for my work?

There are some cases where work is carried out and building regulation approval is not sought for.
If works are carried out and do not comply with the building regulations, the local authority can prosecute the builders with an unlimited fine and they can enforce the building regulations on you, the owner, forcing you to make good the works or they will do it and claim the costs from you.
When it comes to selling the property, a building regulations completion certificate will be requested to prove that the extension works comply with the building regulations and have been carried out to the correct standard.
You can regularise works carried out without building regulations, however this usually involves opening areas such as the ceiling to check the works comply with the building regulations. If problems are found during this inspection, they will need to be made good prior to receiving a regularisation certificate.
The buyer may get a quote from a builder for putting the works right and they can use this to negotiate the value of the property.
An indemnity insurance policy can be taken out on the works that do not comply with the building regulations; however, issues will likely arise again when the property is re-sold.


Building regulations are one of the most important parts to building works nowadays.
When carrying out extension works, ensure that it has been designed in compliance with the approved documents and that a building control body (local authority or private inspector) is appointed prior to starting the works on site. The builders must be aware of the building regulations and carry the works out to a high standard in order to obtain the building control completion certificate upon completion of the works.