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Do I need planning permission for an extension in Ireland?

Only if it exceeds the exemption. A single-storey rear extension up to 40 m² is generally exempted development under Class 1 of Schedule 2 to the Planning and Development Regulations 2001, but front or side extensions, larger extensions, and most work at properties with restricted exemptions need full planning permission.

Class 1 of Schedule 2 to the Planning and Development Regulations 2001 (as amended) allows an extension to the rear of a house without planning permission, provided the combined floor area of that extension and any extension built since 1 October 1964 does not exceed 40 m².

The allowance is smaller for anything above ground-floor level, and the limit differs for detached houses compared with terraced or semi-detached houses. At least 25 m² of private open space must remain to the rear of the house after the extension is built, and upper-floor windows facing a boundary must meet a minimum setback distance.

Extensions to the front of a house are not exempted development, and side extensions are only exempt in narrow circumstances. If the extension would exceed 40 m², rise above the height of the existing roof, remove required open space, or the house is a protected structure or has had its exemption removed by an earlier planning condition, full planning permission is required.

Checklist for an exempt rear extension

Confirm each of the following before assuming no permission is needed:

  • The extension is to the rear of the house only
  • Total extension area since 1 October 1964, including this one, is 40 m² or less
  • Any part above ground-floor level fits within the smaller allowance for your house type
  • Height does not exceed that of the existing house
  • At least 25 m² of private open space remains to the rear
  • No protected structure, conservation area or restrictive planning condition applies

Even a fully exempt extension must still comply with the Building Regulations and usually needs a Fire Safety Certificate assessment or disability access statement where relevant.

When to seek confirmation

Because the 40 m² limit is cumulative and earlier owners' works can count against it, get a copy of the property's planning history and, where there is any doubt, apply for a section 5 declaration or consult the local authority before building.

Sources

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

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