Do I Need Planning Permission for an Extension?

A rear extension can be exempted development, meaning no planning permission is needed, when broadly:

• The total floor area of all extensions to the house, including any earlier ones, is no more than 40 square metres
• At least 25 square metres of private open space (usually back garden) remains
• Height limits are met, and the extension is no higher than the house
• Upstairs extensions stay within smaller size limits and set distances from boundaries

The full conditions are detailed, so treat this as a guide and check before you build.

• The extension, together with any earlier ones, goes over the exempt limits
• It extends to the side or front beyond what's allowed
• The property is a protected structure or in an architectural conservation area
• An earlier planning permission for the house restricts further extensions

A planning application usually takes around 8 weeks for a decision, longer if there's an appeal.

Even when no planning permission is needed, every extension must meet the Building Regulations: structure, fire safety, insulation and ventilation. Larger projects also need notices and certification under the Building Control rules. Your designer or engineer should confirm what applies.

Planning is handled by the council for the area: Dublin City Council, Fingal, South Dublin or Dún Laoghaire-Rathdown. If you're unsure whether your extension is exempt, you can ask your council for a formal declaration on whether it needs permission, known as a Section 5 declaration.