Garden room over 30 m²: what you need to know
The short answer
In Ireland, a garden room over 30 m² needs planning permission. The 30 m² includes any sheds or garages you already have. The one exception is a Class 3A garden home of 32 to 45 m², which is exempt but must be a proper self-contained home with extra conditions. A planning application for a garden building costs €34 in council fees, and the council decides within 8 weeks.
On this page
Your four options
| Option | Size | Good for |
|---|---|---|
| Stay at 30 m² or less | Up to 30 m² in total | Most offices, gyms and studios. No application needed. See the rules. |
| Class 3A garden home | 32 to 45 m² | Somewhere for family to live. Must meet Building Regulations and be notified to the council. See garden homes. |
| Apply for planning permission | Any size | A bigger studio, gym or office that isn't a home. |
| Build an extension instead | Up to 45 m² exempt | Space attached to the house. See below. |
Applying for planning permission
A garden room application is one of the simplest a council deals with, but it follows the same process as any other:
- Get drawings prepared. Site location map, site layout plan, and floor plans and elevations of the room. An architect, engineer or architectural technician usually prepares these, and some garden room companies arrange them.
- Publish a newspaper notice in a paper approved by your council, and put up a site notice where it can be read from the road.
- Lodge the application within 2 weeks of the newspaper notice, with the €34 fee. Most councils accept applications online.
- Wait for the decision. Neighbours and anyone else can make a submission in the first 5 weeks. The council decides within 8 weeks, or asks for further information, which pauses the clock.
- Wait for the appeal period to pass. If nobody appeals within 4 weeks, the council issues the final grant. Don't start building before the final grant.
What it costs
| Item | Cost |
|---|---|
| Council fee, garden building at a house | €34 |
| Retention, if it's already built | €102 or €2.50 per m², whichever is more |
| Submission by a neighbour | €20 (paid by them) |
| Appeal to An Coimisiún Pleanála | €220 |
| Drawings and newspaper notice | Get quotes |
The council fee is small. Budget mainly for the drawings, and for the time: about 3 months that the room can't be built in.
What the council looks at
- Scale: whether the building is in proportion to the house and garden, and how much garden is left.
- Neighbours: height near the boundary, overshadowing and windows that overlook.
- Use: councils often attach a condition that the room is used only for purposes connected with the house, and not lived in, let or used for a business. See sleeping in a garden room.
- The development plan: conservation areas, protected structures and scenic designations.
Building it as an extension instead
Since July 2026, an extension at the back of the house is exempt up to 45 m², with its own conditions on height, the 25 m² of garden left and previous extensions. If what you really want is more living space, an extension may get you more floor area without an application. See garden home or extension.
Check what size you can build
See the largest exempt garden room your garden allows, drawn to scale.
Watch out for UK advice
Search for "garden room over 30 m²" and many results come from UK sites. In the UK, permitted development limits garden buildings mainly by height and how much of the garden they cover, and 30 m² is a building control threshold. None of that applies in Ireland, where the 30 m² floor area cap is the planning limit and the 25 m² of garden you must keep often limits you first.
Common questions
Can I build a garden room over 30 m² in Ireland without planning permission?
Not as a garden room. The exemption covers garden buildings up to 30 m² in total. The only larger exemption is Class 3A, for a 32 to 45 m² detached home in the back garden, which has its own conditions, including Building Regulations compliance and notifying the council. Anything else over 30 m² needs planning permission.
How much does planning permission for a garden room cost?
The council fee for a garden building at a house is €34. Most of the real cost is the drawings and the newspaper notice. If the room is already built, a retention application costs €102 or €2.50 per m², whichever is more.
How long does planning permission take for a garden room?
The council has 8 weeks to decide a valid application, then there is a 4-week appeal period before the final grant. Allow 3 to 4 months from preparing the drawings to the final grant, longer if the council asks for further information or someone appeals.
Is the 30 m² limit the same in the UK?
No. Many top search results for this question come from UK sites, where the rules are different: UK garden buildings are limited mainly by height and the share of the garden they cover, and building control applies over 30 m². In Ireland, the 30 m² floor area cap itself is the planning limit.
Sources
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