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Extensions, Sheds & Garages


What type of extension, shed, garage did you want to build?

Note:  Please view General Notes on Exempted Development after completing this self-assessment.

Can I build an extension?

Small scale domestic extensions, including conservatories, do not require planning permission if the extension is to the rear of the house and

  • the original floor area of the house is not increased by more than 40 square metres. It is important to note that where the house has been extended before, the floor area of the extension you are now proposing and the floor area of any previous extension, including those for which you got planning permission, cannot exceed 40 square metres;
  • for terraced or semi-detached houses, the floor area of any extension above ground level does not exceed 12 square metres, this includes any previous extensions carried out;  
  • where the house is detached, the floor area of any extension above ground level shall not exceed 20 square metres;
  • any extension above ground level is at least 2m from any boundary;
  • any extension does not reduce the area of private open space, reserved for the occupants of the house, to less than 25 square metres.

There are also rules about the height allowed in such an extension. These are that -

  • if the rear wall of the house does not include a gable, the height of the walls of the extension must not exceed the height of the rear wall of the house.
  • if the rear wall of the existing house has a gable, the walls of the extension (excluding any gable being built as part of the extension) shall not be higher than the side walls of the house;
  • in the case of a flat roofed extension, the height of the highest part of the roof may not exceed the height of the eaves or parapet. In any other case, no part of the new roof may exceed the highest part of the roof of the house;
  • a gable is the upper part of a wall (normally triangular), between the sloping ends of a pitched roof.

There are also rules about the required distances between windows in extensions and the facing boundary of the adjoining property and the use of the roof of the extension. These are that -

  • any extension proposed at ground level as part of an extension should not be less than 1 metre from the boundary they face.
  • any windows proposed at above ground level should be not less than 11 metres from the boundary they face;
  • the roof of any such extension should not be used as a balcony or roof garden.
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Can I build a front porch?

You can build a porch without planning permission as long as it does not exceed 2 square metres in area and is more than 2 metres from any public road or footpath. Where the porch has a tiled or slated pitched roof it must not exceed 4 metres in height or 3 metres for any other roof type. A front porch within these limits is the only type of development allowed to extend beyond the front wall of the building (the building line) and still remain exempted.

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Can I convert my garage to domestic use?

The conversion for use as part of a dwelling house (e.g. as a living room or bedroom) of a garage, store. shed, etc. attached to the rear or side of a house is normally exempted development, subject to the 40 square metre limit and conditions as set out in "Can I build an extension?".

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Can I build a garage?

You can build a garage, carport, shed, greenhouse, kennel for domestic pets, etc., as long as it does not extend out in front of the building line of the house and does not exceed 4 metres in heighr, (if it has a tiled or slated pitched roof), or 3 metres (if it has any other roof type). The floor area limitation for exempted development is 25 square metres (which  includes the  floor area of any existing garage,shed etc.  for example, if there is an existing shed of 15 square metres then the exempted limitation would be 10 square metres) and the structure may not be lived in, used for commercial purposes or for keeping pigs, poultry, pigeons, ponies or horses. Garages, sheds, etc. to the side of the house must match the finish of the house. You cannot reduce the open space at the side or rear of the house below 25 square metres.

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Tools & Resources

Android Phone app now available for free on the Android Marketplace.  Search for "Mayo Planning Search."

Forward Planning Updates

Variation No. 5 to the Castlebar and Environs Plan 2008-2014 was made on the 10th July 2017

Castlebar & Environs Development Plan 2008-2014


Deferral of notices for the Ireland West Airport Knock Local Area Plan 2012-2018

Cheif Executive's Report






  More Mayo County Council and Local Government Websites