House Extension Guide

1. Types of house extension

The main types of house extension are as follows:

Single storey house extension

Single storey extensions are constructed so that one or more the walls border the existing house. Often a single storey extension is used to increase the size of a kitchen and/or living area.

When considering a single storey house extension there are some key factors to consider including:

  • The additional living space you want to create.
  • Any impact a single-storey extension would have on your neighbours.
  • How the new roof system will work with the existing roof.
  • Planning permission limitations.
  • Building control limitations.
  • Structural calculations.
  • Conservation area.

Multi-storey house extension

A multi-storey house extension is an extension spanning over more than one floor. A multi-storey extension will drastically increase the houses living space.

When considering a multi-storey house extension there are some key factors to consider including:

  • The additional living space you want to create.
  • Any impact a multi-storey extension would have on your neighbours.
  • How the new roof system will work with the existing roof.
  • Planning permission limitations.
  • Building control limitations.
  • Structural calculations.
  • Conservation area.

Over-structure extension

An over-structure extension is just like it sounds, built over an existing structure of your house. This type of extension is often built on top of a garage, kitchen or dining room. The technical requirements to ensure the supporting structure is adequate is quite complex. It might be necessary to install strengthening supports which will require the input of a structural engineer.

When considering an over-structure house extension there are some key factors to consider including:

  • The additional living space you want to create.
  • Any impact a over-sructure extension would have on your neighbours.
  • How the new roof system will work with the existing roof.
  • Planning permission limitations.
  • Building control limitations.
  • Structural calculations.
  • Conservation area.

2. Planning Permission Process Explained

Understanding when planning permission is required can be a very complicated matter. Each council has its own Planning Control office with the responsibility is to protect the public's interest with regards to the local environment and to maintain the character and amenity of an area is not adversely affected.

First steps you should take

We advise you to first talk to your neighbours this will ensure any queries and disagreements can be dealt with before submitting your proposed extension for Building Control approval. Often neighbours will be concerned about disruption to light and privacy. Overcoming these concerns early on will help make the planning process run more smoothly. Also Building Control will almost certainly contact your neighbours as part of the planning permission process.

Do you need planning permission for your proposed extension?

It is important to contact your local Council Planning Department to check whether your proposed extension requires planning permission, if you fail to get the required planning permission the extension may have to be altered or even demolished proving very costly. You can find your local council website here.www.gov.uk/find-your-local-council

The Government Planning Control website is an excellent resource to determine if planning permission is required.

The Government planning control website states that:

An extension or addition to your house is considered to be a 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 extension must not extend beyond the rear wall of the original house* by more than three metres if an attached house or by four metres if a detached house.
  • In addition, outside Article 2(3) designated land* and Sites of Special Scientific Interest the limit is increased to 6m if an attached house and 8m if a detached house until 30 May 2019.
  • These increased limits (between 3m and 6m and between 4m and 8m respectively) are subject to the prior notification of the proposal to the Local Planning Authority and the implementation of a neighbour consultation scheme. If objections are received, the proposal might not be allowed.
  • 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 designated land* no permitted development for rear extensions of more than one storey.
  • On designated land no cladding of the exterior.
  • On designated land no side extensions.

* The term "original house" means the house as it was first built or as it stood on 1 July 1948 (if it was built before that date). Although you may not have built an extension to the house, a previous owner may have done so.

* Designated land includes conservation areas, national parks and the Broads, Areas of Outstanding Natural Beauty, and World Heritage Sites.

These guidelines often get changed we advise you check the latest guidelines here.

Some councils limit the scope of permitted developments due to conservations areas or listed buildings, we advise you to check your local councils website for further information.

Lawful Development Certificate

I many cases where it has been decided the proposed extension is covered as a permitted development it is advisable to apply for a Lawful Development Certificate. This will give you peace of mind and proof that your extension is lawful and if you choose to later sell the property will help answer any queries raised by potential buyers.

We also strongly advise you to talk to an Architect or Chartered Building Surveyor as they will be able advise you if Planning permission is required.

The application process

To apply for planning permission you will first need to contact your local planning department they will be able to send you all the required forms. These associated application fees will need to be paid:

  • £150 in England
  • £166 in Wales

Along with your completed planning application form you will need to send plans of the proposed extension in a specified scale of 1:50 or 1:00 and site plans to scale of 1:500 or 1:250.

3. Building Regulations Process Explained

After you have received planning permission you will need to apply for Building Regulations. Building Regulations cover the minimum building standards by UK Law. You can apply for Building Regulations online or by phone and will need to determine which application you need to submit, this will be dependant on the extent of works and they will be able to advise.

Construction of the project can start 48 hours after a application is submitted. It may transpire that the building notes on the drawings need to be amended to building controls approval which will mean that the works onsite might need to be amended reflecting these changes.

During construction a council building inspector will visit the site to ensure all building regulations are being met.

Once construction has finished and your house extension is complete your Council will issue you with a Completion Certificate. This is an important document and should be kept in your records as it will be needed should you choose to sell the property at a later date.

4. Why use an Architect or Chartered Building Surveyor

Employing a Architect or Chartered Building Surveyor is highly recommended when undertaking a large scale project such as a house extension. An Architect or Chartered Building Surveyor will be able help you with the following:

  • Advise you about Planning Control processes.
  • Turn your ideas and requirements into a viable building plan.
  • Draw up detailed plans which will be required for Planning Control & your builder.
  • Ensure the proposed extension will pass planning permission (if required).
  • Ensure the plans meet Building Regulations.
  • Produce a schedule of works.
  • Assist with the tendering process.
  • Advise on contractors suitable for your project.

House Extension Expert Advice & Quotes

If you have any questions about your extension we will be more than happy to help. For free advice and/or quote please complete our online enquiry form by clicking on 'Request Free Estimate' at the top of this page or alternatively call us on 01273 857886 and we will be happy discuss your requirements.

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