Broadly speaking, the construction of an extension or conservatory does not require planning permission when it is to the rear of the house; however, any query from the public of this nature should be dealt with subject to the provisions of Part 1 of the 2nd Schedule to the Planning and Development Regulations, 2001.
The following should be seen only as general guidelines;
Terraced and Semi-Detached Houses: If the house has not been previously extended, the floor area of the proposed extension cannot exceed 40 sq metres. This exemption also allows for extensions above ground-floor level (if the house is semi-detached or terraced, the area of the above ground extension cannot exceed 12 sq. m). This means, for a typical semi-detached house, one could have a ground floor extension of 28sq. m & 2nd floor extension of 12sq m without applying for planning permission. Any above ground floor extension shall be a distance of not less than 2 metres from any party boundary.
Detached Houses: As with terraced and Semi-detached above, the overall area of extension must be less than 40 sq. metres. This exemption also allows for extensions above ground floor level, the are above ground floor are cannot exceed 20 sq. m. One could therefore have a ground floor extension of 20 sq. m., and a 2nd floor of 20 sq. m. Any above ground floor extension shall be a distance of not less than 2 metres from any party boundary..
Both Cases: If the proposed extension is in addition to an existing extension (post 01-10-1964), overall areas of all extensions must not be more than 40 sq. m. - including extensions which needed permission, e.g. to side of house.