Garden annexes and granny flats in Ireland
The short answer
In Ireland there are three ways to build a garden annexe or granny flat. A detached garden home of 32 to 45 m² is exempt from planning under Class 3A since July 2026, with conditions. An attached "family flat" needs planning permission, and councils usually limit it to around 50 to 75 m² for a family member. Anything bigger, or fully independent, needs planning permission as a separate home.
On this page
Three ways to build an annexe
| Route | Size | Planning |
|---|---|---|
| Detached garden home (Class 3A) | 32 to 45 m² | Exempt if every condition is met; notify the council |
| Attached family flat | Council limits, often 50 to 75 m² | Planning permission |
| Separate dwelling in the garden | Any | Planning permission as a new home; often refused |
Detached: a Class 3A garden home
Since 27 July 2026, you can build a detached home of 32 to 45 m² in your back garden without planning permission. This is the closest thing Ireland has to the UK's garden annexe. The main conditions:
- 32 to 45 m², including any sheds or garden rooms you keep.
- At least 25 m² of garden left, and 0.6 m from boundaries.
- Connected to the main house's services, with no separate entrance from the road.
- Built to the Building Regulations, with the council notified 14 days before work starts.
- Not sold separately, and not used for short-term lets.
- Work must be finished by 31 December 2030.
See Class 3A garden homes for every condition, and the layouts for what fits in 32 to 45 m².
Check your garden
Go through every Class 3A condition for your house and garden.
Attached: a family flat
Before Class 3A, the usual way to add a granny flat was an extension built as a family flat, with planning permission. Councils still allow these, under policies in their development plans. Two examples:
| Council | Typical rules |
|---|---|
| Louth | For an immediate family member; generally up to 50 m²; internal link if attached; same ownership as the house; not sold or let separately. |
| Fingal | For an immediate family member, with need shown; up to 75 m² internal floor area; entrance through the main house unless unavoidable; garden not subdivided; capable of becoming part of the house later. |
Expect conditions such as using it only for a family member, and reverting to part of the main house when it's no longer needed. Check your own council's development plan; the details vary.
Bigger or separate: planning permission
A larger detached annexe, one with its own access from the road, or one built to be sold or let separately is a new house. It needs full planning permission, and councils often refuse a second house in a back garden. Talk to the council's planning section before you spend money on drawings. See applying for planning permission.
What doesn't count
- A garden room: exempt up to 30 m², but not for living or sleeping in. See can you sleep in a garden room?
- A mobile home or caravan: you can store one, but living in it needs permission. See mobile homes and log cabins.
Next steps
Common questions
Do I need planning permission for a garden annexe in Ireland?
Not if it's a detached Class 3A garden home of 32 to 45 m² that meets every condition, including Building Regulations and notifying the council. An attached annexe or "family flat" usually needs planning permission, and councils have their own policies on size and access. A garden room can't be used as an annexe to live in.
What is the difference between an annex and an annexe?
Nothing in practice. "Annexe" is the usual Irish and British spelling and "annex" the American one. Irish planning policies tend to say "family flat" or "granny flat", and the 2026 exemption calls it a detached habitable structure, which we call a garden home.
How big can a granny flat be in Ireland?
Without planning permission, a detached garden home can be 32 to 45 m², including any sheds you keep. With planning permission, councils set their own limits for family flats: for example, Louth generally allows up to 50 m² and Fingal up to 75 m².
Can I rent out a garden annexe?
A Class 3A garden home can be let, but not sold separately or used for short-term lets. Family flats granted planning permission usually have a condition that they are only for a family member and can't be let or sold separately.
Sources
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