Planning permission for a house extension
Since 27 July 2026 you can build up to 45 m² behind the house without applying for planning permission. That 45 m² includes every extension added since 1964 and any attached garage you convert. The extension can't rise above the house, the house has to keep 25 m² of private open space, ground-floor windows need 1 m or more to the boundary they look onto, and no more than 12 m² of it can be upstairs on a semi or terrace (20 m² on a detached house). Before that date the limit was 40 m².
The 45 m² exemption from 27 July 2026 condition by condition, what each kind of house extension needs, and the application when you need one.
Free and no obligation. Your plan goes to one builder, not a list.
- 45 m²exempt behind the house, up from 40 m²
- 8 mupstairs window to the boundary, down from 11 m
- €34council fee for an extension application
- 8 + 4 weekscouncil decision, then time for appeals
The eight conditions
Class 1 of the exempted development regulations sets them, in the version that S.I. No. 338 of 2026 brought in on 27 July 2026. Meet all eight and there is no planning application to make:
- Behind the house, or in the garage. Class 1 is about building onto the rear of the house, and about turning an attached garage, store or shed at the back or the side into living space. A new extension at the side isn't covered.
- 45 m² between all of them. Add up every extension put on the house since 1 October 1964, including any built with planning permission, and the conversion. Together they can't pass 45 m². Until 27 July 2026 the figure was 40 m².
- A small upstairs. Above the ground floor, 12 m² is the most on a semi-detached or terraced house and 20 m² on a detached one, and any upstairs part stays 2 m clear of a party boundary.
- Below the house's own height. The new walls stop at the height of the house's back wall (its side walls, if the back is a gable). A flat roof stops at the eaves or parapet; a pitched roof goes no higher than the top of the house roof.
- 25 m² of garden kept. After the extension, 25 m² or more of private open space has to remain within the grounds of the house.
- Windows set back. 1 m between a ground-floor window and the boundary in front of it, and 8 m for an upstairs window, down from 11 m before the change.
- A roof you don't stand on. The extension's roof can't be used as a balcony or a terrace.
- Part of the main house. The exemption is for extending the house itself, not for a second home at the end of the garden.
What changed on 27 July 2026
| What | Until 26 July 2026 | From 27 July 2026 |
|---|---|---|
| Total floor area behind the house, counting extensions since 1964 | 40 m² | 45 m² |
| Upstairs window to the boundary it faces | 11 m | 8 m |
| Private open space the house keeps | 25 m² to the rear of the house | 25 m² in total within the grounds of the house |
| Using the extension's roof | Not as a balcony or roof garden | Not as a balcony or terrace |
| Which building it applies to | Not stated | The main house only, not a second house in the garden |
| No commencement notice needed up to | 40 m² | 45 m² |
Building control moved its threshold to 45 m² on the same day (S.I. No. 359 of 2026).
Which house extensions need permission
- Ground floor, behind the house: no application up to 45 m², if all eight conditions are met.
- Two storeys: nearly always an application, because upstairs stops at 12 m² on a semi or terrace and 20 m² on a detached house.
- At the side: always an application. Class 1 doesn't cover new building beside the house.
- Wraparound: an application for the side part, in most cases.
- Garage conversion: no application for an attached garage at the side or back, within the 45 m².
- A room over the garage: an application, because it is new building upstairs at the side.
Plan your house extension
Four quick taps, and your plan fills in as you answer: what it costs, whether it needs planning permission and how long it takes. Contact details come last, and only if you want a builder to price it.
25 m² single-storey rear, mid-range finish: €52,000 to €65,000, including VAT and fees.
How the estimate is worked out
Every kind of extension has a build rate per m² for each region of Ireland, VAT at 13.5% included. A standard finish uses the lower half of that range and mid-range the upper half; high spec or a wall of glass moves the build to the glazed rate. Design, engineer and BER fees go on top, with anything you tick (an en-suite, a kitchen, a steel beam into the house) priced at your finish. A garage conversion gets one price for the whole job, since the walls and roof are already standing. Totals are rounded to the nearest €1,000. Use it to plan with. It isn't a quote: a builder prices your house after seeing it.
What can take the exemption away
Three things can take the exemption away. A condition in the planning permission your house was built under can remove it, and newer estates often have one. On a protected structure, work that would affect its character isn't exempt. And no extension is exempt if it would obstruct a public right of way or create a traffic hazard.
The permission your house was built under is on the council's online planning search. Look in it for a condition about future extensions or exempted development before you rely on the 45 m².
If you aren't sure, ask the council for a section 5 declaration: for €80 it decides in writing whether your plan is exempt.
When you need planning permission
- Plans and notices. Your designer prepares the drawings. Within the two weeks before you lodge the application, a notice goes in a local newspaper and a site notice goes up at the front of the house.
- Lodge it with the council. €34 for an extension to a house.
- Submissions and the decision. For the first five weeks anyone can comment on the application. The council decides within 8 weeks, unless it asks you for further information.
- Appeals. For 4 weeks after the decision, you or anyone who made a submission can appeal to An Coimisiún Pleanála. With no appeal, the permission is final.
That's about 12 weeks from lodging to a final permission, with no appeal and no request for more information. The planner builds this into your timeline when your plan needs it.
Questions before you build
What size of extension can I build without planning permission?
45 m² behind the house in total. Older extensions added since 1964 come out of that figure, and the other seven conditions still apply. The limit was 40 m² before 27 July 2026.
Does the extension we built years ago count?
If it went up after 1 October 1964, yes, even if it had planning permission. A converted attached garage counts too.
Can a two-storey extension go up without planning permission?
Only a small one: 12 m² upstairs on a semi or terrace, 20 m² detached, kept 2 m from a party boundary, and 8 m between an upstairs window and the boundary opposite. Most two-storey extensions are bigger, so they need an application.
Does a side extension need planning permission?
Yes. Class 1 covers building behind the house and converting an attached garage, shed or store. New building at the side is neither.
How do I find out for certain whether my extension is exempt?
Ask the council for a section 5 declaration. For €80 it decides in writing whether your plan is exempted development. It's worth it if you're close to a limit or your estate's permission has conditions.
What if we build without planning permission we needed?
The council can serve an enforcement notice. It also surfaces when you sell: the buyer's solicitor will want evidence that the extension was exempt or had permission. You can apply for retention permission afterwards, but the council can refuse it.
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