Garden room and granny flat planning permission in Ireland

Do you need planning permission for a garden room?

It depends on how the room will be used and how big it is.

• Garden room for everyday use at home: can be exempt under Class 3.
• Small detached home for a family member: may be exempt under the new Class 3A, with strict conditions.
• Anything else, such as a separate home to rent or sell: needs planning permission.

When a garden room is exempt: Class 3

Class 3 in Part 1 of Schedule 2 covers a tent, awning, shade, greenhouse, garage, store, shed or similar structure within the curtilage of a house. S.I. 338 of 2026 raised the total area limit from 25 to 30 square metres from 27 July 2026. The conditions are:

• The structure cannot be forward of the front wall of the house.
• All such structures in the garden, added together, cannot exceed 30 square metres.
• At least 25 square metres of private open space must remain at the rear or side of the house.
• The structure cannot be higher than 4 metres with a tiled or slated pitched roof, or 3 metres in any other case.
• A structure to the side of the house must have external finishes, and roof covering where tiled or slated, that match the house.
• The structure cannot be used for human habitation, for keeping pigs, poultry, pigeons, ponies or horses, or for any purpose other than one incidental to the enjoyment of the house.

A bed-sit, guest room used as a home or a rented unit does not fit Class 3, because it is habitation.

Home offices

Many people want a garden room to work from. The test in Class 3 is a purpose incidental to the enjoyment of the house. The Regulations do not say whether running a business from the room fits this test. Ask the council before you build.

Granny flats and family flats

There are three routes. Each has strict conditions.

Attached to the house: Class 1

A granny flat built as a rear extension to the main house follows the extension rules. See the extension guide. From 27 July 2026, the limit is 45 square metres for a house not extended before.

Detached in the rear garden: Class 3A

S.I. 340 of 2026 added Class 3A for a detached house in the rear garden of a principal house. Some of the main conditions are:

• The work must be commenced and completed between the date of signing and 31 December 2030.
• The area must be at least 32 square metres, and no more than 45 square metres when counted with other Class 3 structures.
• It can only be occupied together with the main house. It cannot be sold or subdivided separately.
• The height limit is 4 metres with a tiled or slated pitched roof, or 3 metres in any other case.
• It must stay at least 0.6 metres from any wall or party boundary. Windows must be at least 0.6 metres from the boundary they face.
• At least 25 square metres of private open space must remain.
• No new vehicle or pedestrian access onto a road. It needs its own pedestrian or wheelchair access inside the property.
• No separate connection to water or wastewater utilities.
• No use for short-term letting.
• The main house must be the owner’s sole or main residence when work starts.
• It cannot be temporary, such as a caravan or mobile home.
• The council must be notified at least 14 days before work starts.

The Building Regulations still apply, including fire safety. Class 3A cannot be used if the main house has been subdivided.

Splitting the house: Class 1A

Class 1A, from S.I. 339 of 2026, allows a house to be divided into no more than two units. Each must be at least 32 square metres and self-contained. It also needs a 14-day notification and applies to work started and finished by 31 December 2030.

When you need to apply

Apply for planning permission if any of these is true.

• The garden structures total more than 30 square metres.
• The structure is forward of the front wall, or too high.
• It would leave less than 25 square metres of private garden.
• Someone will live in it and it does not meet Class 3A.
• It will be used for a business and the council says that is not incidental to the house.
• A condition on an earlier permission rules it out. Article 9 removes the exemption if the work breaks a condition.

Special cases

• Protected structures: under section 57 of the 2000 Act, works are exempt only if they do not materially affect the character of the structure.
• Architectural conservation areas: Article 9 removes the exemption for exterior works that would materially affect the character of the area.
• Natura 2000 and other nature sites: if the work needs an appropriate assessment, it is not exempt.
• Flood risk: Article 9 does not list flood risk as a reason to lose the exemption. Check the council’s flood maps before you build.
• Apartments: the Regulations say Class 3 applies to a house, not to a flat or apartment.

Costs and fees

The national fee for works within the curtilage of an existing house is €34. Retention permission costs more. Use the planning fee calculator for the exact amount.

Checklist before you build

• Do all garden structures, with the new one, total 30 square metres or less?
• Is the room behind the front wall of the house?
• Is it within 3 or 4 metres in height, depending on the roof?
• Will 25 square metres of private garden remain?
• Will it be used only for something incidental to the house, not as a home?
• For a granny flat, have you read every Class 3A condition?
• Have you checked the Building Regulations and utilities?

Next steps

Ask the council for a pre-planning meeting, especially for a granny flat or a home office. These meetings come from section 247 of the 2000 Act. The advice does not grant permission.

If you need to apply, read how to apply. For a simpler outbuilding, see the shed guide. You can also browse local planning applications.

The law is changing

The Planning and Development Act 2024 is being brought into force in stages. Classes 3 and 3A were made in July 2026 under the 2000 Act, and Class 3A ends for new work on 31 December 2030. Check the Department of Housing’s website for which parts of the 2024 Act are in force.

Check before you build

Garden room and granny flat rules depend on the exact site, the main house and its planning history. A pre-planning report checks zoning, protected structures and nature sites at an address, so you can see the main limits early. Use the pre-planning report or the planning permission checker. Then confirm with your council.