Northern Ireland Planning Service

Home owners: Extensions, Alterations & Additions

Building an extension

Planning permission is not required provided that:
1. The ground area covered by the extension and any other buildings within the boundary of the property, excluding the original house, is not more than half the total area of the property.
2. Any part of the extension is not higher than the highest part of the roof of the existing house.
3. The eaves of the extension are not higher than the eaves of the existing house.
4. Any part of the extension does not extend beyond any wall facing a road if it forms the principal or side elevation of the original house.
5. The eaves are no more than 3 metres in height if any part of the extension is within 2 metres of the property boundary.
6. The materials used in exterior work, except in the case of a conservatory, are of similar appearance to the existing house. (see section "conservatories" below)
7. An upper floor window on a side elevation within 15 metres of a boundary with another house is obscure glazed; and is non – opening unless the parts which can be opened are more than 1.7 metres above the floor of the room in which the window is installed.
8. A side extension does not exceed 4 metres in height or be wider than half the width of the original house.
9. In a single storey extension (see illustration 1):-
   a. the extension does not extend beyond the rear wall of the original house by more than 4 metres for a detached house or 3 metres for any other type of house;
   b. the height of the extension does not exceed 4 metres;
   c. no part of the extension is within 3.5 metres of any property boundary with a road opposite the rear wall of the house.
10. In an extension with more than one storey (see illustration 2): -
   a. the extension does not extend beyond the rear wall of the original house by more than 3 metres;
   b. no part of the extension is within 7 metres of the property boundary opposite the rear wall of the house;
   c. the roof pitch of the enlargement is as far as practicable the same as that of the original house.
11. If you live in a house within a conservation area, World Heritage Site, area of outstanding natural beauty or National Park-
   a. no part of the exterior of the house is clad with stone, artificial stone, pebbledash, render, timber, plastic or tiles;
   b. the extension is not more than 1 storey or 4 metres in height;
   c. no part of the extension extends beyond a principal or side elevation of the original house.
Note: Measurements are always calculated using external measurements.
If you live in a house which is a listed building, it is likely that you will need Listed Building Consent for any building operations. If the development is within the curtilage of a listed building you may need to submit a planning application for the work unless listed building consent has already been granted. Your local area planning office will be able to advise you.
Illustration 1: Side and rear single storey extensions to detached house
Illustration 1
Illustration 2: Two storey rear extension to terraced house
Illustration 2

Conservatories

A conservatory attached to the house will be treated as an extension and therefore will need to comply with the rules set out in Section 1. A free standing conservatory will be subject to the criteria set out in Section 6 – Garden Sheds, Greenhouses and Other Buildings”.

Other dwelling attached to a house e.g. a granny flat

Planning permission is required if it is a separate and self-contained unit. If it is not a separate and self-contained unit it will be treated as an extension and therefore will need to comply with the restrictions and limitations as set out in Section 1.

Converting a house, or part of it into one or more flats or apartments

Planning permission is required for converting a house or part of a house into one or more flats, even though building work may not be involved as this will be treated as a change of use.

Changing part of a house for homeworking purposes

The use of any part of a house for homeworking purposes may not need planning permission but this will depend on the scale and nature of the use. Check with your local area planning office.

Demolition

If your house lies within a conservation area (see glossary) you may need consent for demolition. You may also need to apply for planning permission for demolition if your house is located within an Area of Townscape or Village Character. In all cases it is recommended that you consult your local area planning office with the details of the particular proposal and seek their advice.
If you live in a house which is a listed building, it is likely that you will need Listed Building Consent for any building operations. If the development is within the curtilage of a listed building you may need to submit a planning application for the work unless listed building consent has already been granted. Your local area planning office will be able to advise you.