Extension without planning permission: the 2026 size limit
You do not need planning permission for an extension to the rear of your house if its floor area is no more than 45 m², counting every earlier extension built after 1 October 1964. The limit rose from 40 m² to 45 m² on 27 July 2026, and the other conditions below still apply.
What counts as an extension
The exemption is Class 1 of the Planning and Development Regulations 2001, as replaced by S.I. No. 338 of 2026. It covers:
- a new extension at the back of the house, conservatories included;
- turning a garage, store, shed or similar structure attached to the rear or side of the house into part of the house.
The size limits
| Part of the extension | Largest floor area without permission |
|---|---|
| Whole extension, with all earlier extensions since 1 October 1964 | 45 m² |
| Upstairs part, terraced or semi-detached house | 12 m² |
| Upstairs part, detached house | 20 m² |
The upstairs limits are part of the 45 m², not on top of it. Earlier extensions count even if they had planning permission.
The other conditions
- Distance upstairs. Any part above the ground floor must be at least 2 m from any party boundary.
- Height. The walls cannot be higher than the rear wall of the house. If the rear wall has a gable, the limit is the height of the side walls. A flat-roofed extension cannot rise above the eaves or parapet height; any other extension cannot rise above the highest part of the roof of the house.
- Open space left. The extension cannot reduce the private open space kept for the people who live in the house below 25 m². S.I. No. 338 of 2026 words this as the total private open space within the curtilage of the house; the earlier text spoke of the space to the rear.
- Windows. A ground-floor window must be at least 1 m from the boundary it faces. An upstairs window must be at least 8 m away (it was 11 m before 27 July 2026).
- Roof. The roof of the extension cannot be used as a balcony or terrace.
- Main house only. The exemption cannot be used for a second, detached house built in the garden (garden house rules).
When the exemption does not apply
An exemption does not apply in some cases, for example if the work would break a condition of an earlier planning permission or extend an unauthorised structure (article 9 of the Planning and Development Regulations 2001). Citizens Information also warns that there are restrictions if the house is a protected structure or in an architectural conservation area.
If you are not sure, anyone can ask the council in writing, with the prescribed fee, for a declaration on whether the work is exempted development (section 5 of the Planning and Development Act 2000). The Act gives the council 4 weeks from receiving the request, or 3 weeks from receiving any further information it asks for. In exceptional cases the council can take longer, if it writes to you within that time with its reasons and the date it expects to decide.
If your extension is bigger
Over 45 m², or outside any other condition, you need planning permission (what an application costs). The council usually has 8 weeks to decide; see how long planning takes in each council. Applications go through your council or the national online planning portal, planning.localgov.ie.
Other 2026 rules for the roof and garden: dormers, sheds and garden rooms, or check sizes on the drawing of the house.