House extensions

To get more living space in your house you may consider extending it and adding extra room or two depending on planning permission.


Planning permission for any extension is generally required if the extension extends more than 3m for an attached house or 4m if detached. Additionally, planning permission is governed by the following criteria:

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

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

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

  • 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.

  • Eaves and ridge height to be 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 are not to be 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 or balconies

  • Not in conservation area

  • All side-facing windows on upper-floor to be obscure-glazed and any opening to be 1.7m above the floor.


Undertaking an extension on an existing property is a great way to make maximise space potential and add value to the property. If done properly, it is deemed a good investment and will up the property value.

House extensions is becoming more and more popular as it allows you to get extra space without the need to move bigger house and single storey rear extension can be extended by 3m for an attached house or 4m if detached without planning permission (provided they are not on designated land)

The different types of extension are:

  • Single storey  side or rear extension
  • Double or multi storey house extensions
  • Garage conversions and or garage extensions
  • Loft conversions (see loft conversion section)
  • Basement conversions
  • Outbuilding, orangeries and conservatories

One of the most important consideration when undertaking an extension is the effect it will have on its neighbours and it is also important to consider its effect on the property itself in terms of outlook, daylight and external space, which could affect the quality of the house and its value.


Single storey house extension can be at the rear or on the side or both or on an existing outbuilding or garage. The most common ones being single storey rear extension. The design varies from flat roof to pitched tiled roof depending on the existing house design. Pitched tiled roof offers improved appearance and better look and usually lasts longer. Its design however need to take into consideration access to heights where maintenance may be required such as upper floor windows, the roof itself and gutters. The design should not impact emergency escape purposes in case of a fire.

There is however a tendency to consider living roof or green roofs because of their environmental benefits. There are many types of living roof , but generally they can be classified into 2 main categories: extensive in which allows plants are set in a light-weight growing medium or substrate of a depth of between 20mm and 150mm. The intensive living roofs are very much intended for human use and can be designed for a ‘landscaped’ feel with a variety of decorative grasses, shrubs, plants and trees.


Two storey house extension is a common extension type, but in many cases depends on planning approval and will depend on the property type, design and in other situations, more storey may be possible. The key challenge in two or more storey extension is to design the top storeys considering the impact on the light to adjoining properties. An extension must not cause any significant loss of sunlight to principal rooms and gardens of neighbouring properties. Sunlight should be considered, even where extensions comply with the 45° rule, as this can depend on orientation, house layouts, changes in level between and position of adjoining properties. 

External design: A well designed extension should match the existing house and be in character with the neighbourhood. If an extension is to be well designed, it should:

(1) match the original appearance of the housing materials, roof form and scale and proportion of openings, and
(2) It should not adversely affect the quality and appearance of the surrounding area.

Scale: The overall shape, size and position of an extension must not dominate the existing house. 

Roof: An extension should have a roof that matches the original house in design, angle of pitch (slope), shape, colour and materials

Windows and Doorway: The type, proportions, subdivisions and materials of the new windows and doorways should match those of the original house. 

Materials: Extensions should have external finishes to match, as closely as possible, those already found on the house. 


The construction of roof extensions and dormer windows must not dominate the original house. The roof and sides of dormers should be covered in materials to match or complement the main roof. 


Extensions over existing garages need careful consideration. If the garage is well set back from the house, an extension with a roof of matching eaves line and slope is unlikely to create a "terracing" effect. If a garage is level with the front of the house, as is common, then the first floor should be set back by at least 1 metre, possibly incorporating a pitched roof over the set back. 


To get the best of any house extension project, professional advice is key. KPD Construction is established to help to you making the best decision in any extension project.

Our design team and the implementation team will work with you from the inception stage of your project, to develop your idea into feasible realistic project. They will take you through the planning process if applicable, then work through the building regulation drawings including any structural calculations. You will receive expert advice at every stage and we will consult with you to ensure you achieve what you want in the best possible way.


Just give us a call, we will arrange a free site visit. We will look into what you are trying to achieve and work with you to bring your vision into reality. This will include guidance and advice most importantly at the planning and preconstruction stage. If however your plans has been drawn up and the planning or building control approved already, we will give you a free estimate and any advice that you may need to proceed to construction.