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Can I extend the side of my house without planning permission in Ireland?

Sometimes. A side extension can be exempted development under Class 1 of Schedule 2 to the Planning and Development Regulations 2001, but only if it does not project forward of the front wall and it meets separate, more restrictive floor area and height conditions than a rear extension.

A side extension to a house can be exempted development in Ireland, but Class 1 of Schedule 2 to the Planning and Development Regulations 2001 treats side extensions more restrictively than rear extensions. Where the extension is to the side of the house, it must generally be single-storey, must not exceed 4 metres in height, and the floor area of a side extension exempt under this route is capped at a lower figure — typically 12 m² — rather than the full 40 m² allowed for a rear extension, and it still counts toward the overall cumulative limit for the house.

As with front extensions, a side extension must not project forward of the front wall of the house or of any wall fronting a road. It must also maintain a minimum width of private open space to the side of the house after the works, and it must not reduce the area of private open space at the rear below 25 m². Two-storey side extensions are excluded from the exemption entirely and will require planning permission.

Side extensions frequently raise boundary and overlooking issues for neighbours, so councils pay particular attention to their height and positioning relative to the shared boundary. Where the side extension would come close to, or right up against, the boundary with an adjoining property, additional conditions in the regulations concerning boundary walls and eaves height can also come into play.

Conditions for an exempt side extension

Check your proposal against these conditions:

  • The extension is single-storey only
  • The floor area does not exceed the lower side-extension limit set out in Class 1 (generally 12 m²)
  • The height does not exceed 4 metres, with lower limits closer to a boundary
  • The extension does not project forward of the front wall of the house
  • The combined floor area with other extensions stays within the overall 40 m² cumulative limit
  • Adequate private open space remains both to the side and to the rear of the house
  • The property is not a protected structure or within an architectural conservation area

Side extensions are one of the categories most often misjudged by homeowners, since the limits are lower than the well-known 40 m² rear-extension figure.

Common mistakes

The most common mistake is assuming the full 40 m² allowance applies to a side extension in the same way as a rear extension, when in fact side extensions are subject to a separate and lower cap. Homeowners also sometimes overlook that a side extension counts toward, rather than sits alongside, the cumulative 40 m² total for the whole house, which can leave little or no room for a further rear extension later.

Sources

Last reviewed 20 August 2026. General information only — not legal or planning advice.

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