House Extensions: 5 Things to Know Before You Start


Before you starting to build a side extension or a rear extension you should follow few important steps.

1. Inform the council

Even if the extension you are planning to build is within the permitted development you must inform the council of the proposed works via a prior approval application.

An extension or addition to your house is considered to be permitted development, not requiring an application for planning permission, subject to the following limits and conditions:

  • No more than half the area of land around the "original house"* would be covered by additions or other buildings

  • No extension forward of the principal elevation or side elevation fronting a highway

  • No extension to be higher than the highest part of the roof

  • Single-storey rear extensions must not extend beyond the rear wall of the original house* by more than eight metres if a detached house; or more than six metres for any other house If the house is in Article 2(3) designated land* or a Site of Special Scientific Interest, this limit is reduced to four metres if a detached house; or three metres for any other house These limits are now permanent and subject to the neighbour consultation scheme. This requires that the relevant Local Planning Authority is informed of the proposed work via a prior approval application

  • Maximum height of a single-storey rear extension of four metres

  • Extensions of more than one storey must not extend beyond the rear wall of the original house* by more than three metres

  • Maximum eaves height of an extension within two metres of the boundary of three metres

  • Maximum eaves and ridge height of extension no higher than existing house

  • Side extensions to be single storey with maximum height of four metres and width no more than half that of the original house

  • Two-storey extensions no closer than seven metres to rear boundary

  • Roof pitch of extensions higher than one storey to match existing house

  • Materials to be similar in appearance to the existing house

  • No verandas, balconies or raised platforms

  • Upper-floor, side-facing windows to be obscure-glazed; any opening to be 1.7m above the floor

  • On Article 2(3) designated land* no permitted development for rear extensions of more than one storey

  • On Article 2(3) designated land* no cladding of the exterior

  • On Article 2(3) designated land* no side extensions.

​2. Development Drawings

Development Drawings or Construction Drawings are detailed drawings of the building that will be submitted to the building control. If in some cases the building control may accept a more simple drawings is important to have them even for the building works. More details on the drawings will avoid mistakes and confusions with the builder of the extension. These drawings will describe details of the building with more details of how it should be built inclusive sizes.

We can also prepare for interested clients 3D drawings and 3D visualisation of the building.

3. Party wall agreement

Is very, very important to have in place the party wall agreement. Your neighbours will be notified of the building you planning to start and they may be able to stop you doing that. Prior to starting any works you should employ a party wall surveyor that will create all necessary documents and will take photos of the neighbour property.

4. Structural engineer

Structural engineer drawings are the drawings inclusive calculation on the structural works. The Structural Engineer will inspect the property, plans and will prepare detailed drawings of the structural construction.

5. Building Control

Prior to staring any building works you should inform the building control with minimum 5 days before starting works. You can choose to employ council building control or a private Building control company. That will be entirely done by you. The Building Control surveyor will inspect works on structural up to the final parts of the works. You should expect them at least 4 site inspections. parts on which the building control pays more attention:

  • Foundation- he needs to make sure that no trees, water, soil type will not affect the building in the future.

  • Structural beams- he will inspect that beam where done accordingly to the structural engineer drawings and that have been with a in-tumescent fire resistant paint.

  • Structural walls insulation- Walls will have to have the require insulation and include necessary ties and water control system

  • Roof- roof will have to be with at least 150mm insulation and be water tight. There are different type of roof so every roof type will be treated accordingly to the building regulation.

  • Fire- The property will have to have fire and fume detectors and doors to be fire rated.

  • Certificates- gas and electrical - You or your building contractor will have to submit gas certificate and electrical certificate

Building control after all inspections and proves if the property was built accordingly to Building Regulation, will submit the final Building Control Certificate.

If you would like to know more about the design and build process do not hesitate to contact us.

A to Z Design and Build ltd

email: info@atozdesignandbuild.co.uk

tel: 07578930828

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