Garden room and granny flat planning permission — the 2026 Class 1A and 3A exemptions

The seven Greater Dublin Area councils we index received 911 applications describing a garden room, studio, home office or granny flat in the 24 months to 12 September 2026. Of the 581 decided, 519 were granted: 89%. Every one of those applicants paid for notices, drawings and an eight-week wait. From 27 July 2026 a good share of them would not need to. The Planning and Development (Exempted Development) Regulations 2026 (SI 338–344/2026) added two classes to Schedule 2 of the 2001 Regulations. Class 1A is a self-contained unit carved out of the house. Class 3A is a small detached dwelling in the rear garden. Both come with a 14-day notice to the council that you will need again when you sell.

We have not read the statutory instruments in full; irishstatutebook.ie did not return them when we fetched on 12 September 2026. What follows is drawn from South Dublin County Council's published summary of the new classes and from the text of the pre-existing Class 3. Read the instrument, or ask the council, before building.

Class 3: the ordinary garden room, now 30 m²

Class 3 of Schedule 2, Part 1 exempts a structure in the garden of a house: a garage, store, shed, greenhouse, studio or home office. It must be to the side or rear. The aggregate floor area of all such structures may not exceed 30 m² from 27 July 2026 (it was 25 m²). Height is capped at 4 m with a pitched roof, 3 m otherwise. At least 25 m² of private open space must remain behind the house. And it may not be used for human habitation, for keeping pigs or poultry, or for any business beyond what is incidental to the house.

That last condition is the line. A garden office is fine. Sleeping in it, letting it, or plumbing it as a flat took it out of Class 3, and before July 2026 that meant an application or an enforcement letter.

Class 3A: a detached dwelling in the garden

Class 3A, as summarised by South Dublin County Council, exempts a detached "auxiliary" dwelling to the rear of a house with a floor area of 32 to 45 m², linked to the principal house's services. The council's summary carries three conditions worth quoting. "Notification is required to be submitted to the local authority 14 days prior to the commencement of works." The works must be completed by 31 December 2030. And the general conditions on open space, height, boundaries and the house's own permission continue to apply.

The 14-day notice is not an application and no fee is reported for it. It is the first exempted-development class in Ireland to carry a compulsory notice, and the acknowledgement is the document to keep.

Class 1A: subdividing the house

Class 1A exempts the subdivision of an existing house to create one additional self-contained unit of at least 32 m², under the same 14-day notification and the same 2030 completion date. The unit stays within the existing envelope. It is the granny flat or the first-floor let, made lawful without an application. The usual limits on protected structures and on estates whose permission removed exemptions apply, as they do for any class.

Why the notification matters when you sell

A purchaser's solicitor asks the vendor for an architect's or engineer's opinion that any works since 1964 were exempt or permitted. For a Class 3A dwelling that opinion will rest on two documents: drawings showing the floor area and siting within the class, and the council's acknowledgement of the 14-day notice. A dwelling built without the notice is not exempt under the class. The vendor is then back to a retention application. JEArchitecture's practice note puts it as "planning exempt does not mean document-free". A lender valuing a house with a second dwelling on the plot will want the same file.

Building Regulations apply to a garden dwelling in full. Expect a Commencement Notice on the Building Control Management System, fire separation from the boundary and the energy rules for a new dwelling. Water and drainage connections need Uisce Éireann's agreement. The planning exemption lifts none of that.

What the register says about garden rooms

The match is on the description the applicant wrote. It includes applications the new classes now make unnecessary and larger schemes that will still need permission.

One decision from the s.5 register is worth reading before you build. On 17 August 2026 South Dublin County Council declared a 25 m² shed in the rear garden of 42 Tullyhall Drive, Lucan not exempt. Twenty-five square metres was inside the old limit and is inside the new one. The area is never the only test; the open space left behind the house, the height and any earlier structures count too.

Our reading: ask for a s.5 declaration (€80, four weeks) before you order a garden dwelling. Refusals in the register turn on overlooking of the neighbour's garden, a unit with no independent access, and open space left below 25 m². Those are the points a council will look at when your notice lands, and a declaration in hand settles them for the sale as well.

What still needs an application

Anything larger than 45 m², or at the side or front of the house, needs permission. So does a second dwelling on a protected structure or in an Architectural Conservation Area where the works affect character. So does a dwelling in an estate whose parent permission removed exempted-development rights; the condition is on the register and the planning-searches guide explains how to find it. A separate sale of the garden dwelling is a different matter again: the classes create an auxiliary dwelling on the same title, and subdividing the plot is a planning and conveyancing question.

Check the register near you

See what garden-room applications were decided on your street in the Explorer, or type your address into Find. The Lucan and South Dublin County Council place pages carry the council's live figures.

Figures from the register on 12 September 2026 (live callouts refresh hourly); law checked 12 September 2026. Check with the council or a planning consultant before relying on this.

Frequently asked questions

Can I build a granny flat in my garden without planning permission?

From 27 July 2026, yes: detached, to the rear, 32 to 45 m², the other Class 3A conditions met, the council notified 14 days before you start, and the works complete by 31 December 2030. Check the class text and your house's own permission first.

Do I have to tell the council before building a garden dwelling?

Yes. The council's summary of Class 3A says notification must be submitted to the local authority 14 days before works begin. Keep the acknowledgement.

Is a garden office exempt?

Yes, under Class 3, if it is to the side or rear, within 30 m² aggregate and 4 m in height with a pitched roof. Nobody may live in it, and 25 m² of garden must remain.

Can I rent out a Class 3A garden dwelling?

The class creates an auxiliary dwelling. Whether it may be let, and on what terms, depends on the class conditions and on tenancy law. Ask the council and read the instrument before counting on rental income.

What happens after 31 December 2030?

The council's summary says works under Classes 1A and 3A must be completed by that date. Whether the exemption is renewed is a decision for the Minister.