Class 3A garden dwelling · Ireland
Since 2026, you can build a detached dwelling of 32–45 m² in your rear garden without planning permission. It is called Class 3A, it was introduced by S.I. No. 340 of 2026, and it expires on 31 December 2030 — the work must be both started and finished by then.
It is not as simple as "no planning permission needed". There are 20 conditions, and several of them disqualify sites that look perfectly fine at first glance. This page sets out what they mean in practice, and what you still have to do under Building Control — which the exemption does not remove.
Free site visit, no obligation — we tell you on the day whether Class 3A is available to you.Eligibility rules
Worth saying plainly, because it is the question we are asked most: the regulation sets no minimum access width in metres. The 0.9 m figure that circulates online is not one of the 20 conditions. Where 900 mm does become relevant is in the Building Regulations — Part M for the approach to the entrance, and the fire-service access assessment under Technical Guidance Document B, Volume 2. Those are a different question from planning exemption, and a narrow side passage is often solvable.
Compliance after planning
Class 3A exempts you from planning permission. It does not exempt you from the Building Regulations or the Building Control Regulations.
An auxiliary habitable dwelling requires a Commencement Notice with additional documentation: a nominated Design Certifier, an Assigned Certifier, a competent builder, and a Certificate of Compliance on Completion lodged on BCMS. Part A (structure), Part B (fire safety), Part C, Part F, Part L and Part M all apply in full.
This matters later as much as now. When you come to sell, your solicitor will ask for the Certificate of Compliance on Completion and an opinion on compliance with the exemption. A unit built without them is not merely missing paperwork — it is a problem on the conveyancing file, and it is far more expensive to fix after the fact than to do correctly at the time.
A practical Class 3A companion
In a 32–45 m² unit, the bathroom is where most of the cost, the trades and the programme risk sit. It is the only part of the build that needs water, hot water, foul drainage, mechanical extraction and electrical work in the same two square metres — and in a Class 3A unit all of it has to be served from the principal house.
We hold four compact prefabricated ensuite pods in stock in Ireland. A pod arrives factory-assembled, with the shower area, washbasin and toilet provision, waterproof finishes, lighting and extraction already built in, so the site work reduces to positioning and final connection.
Whether a pod suits your project depends on access, the base, drainage falls, hot-water capacity and the ventilation route. We assess that on the same free site visit.
See the pod →Common problems
The 45 m² is combined. A 12 m² garden shed built under Class 3 leaves you 33 m² — barely above the 32 m² minimum.
On a small urban garden, placing a 45 m² unit can leave the main house short of the open space the regulation requires it to retain.
Class 3A units cannot be let, sold or subdivided separately, and cannot be used for short-term letting. If rental income is the point, Class 3A is the wrong route from day one and you need full planning permission instead.
If the principal house was previously divided into units, the exemption is not available.
A separate water meter or a new wastewater connection breaks the conditions. Services must come off the principal house.
It is a finish-by date. Works must be both commenced and completed by 31 December 2030.
Choose the correct route
Evidence of exemption
A Section 5 Declaration is a binding determination from your local authority that your scheme is exempted development.
On a straightforward site you may not need one. On a site with any ambiguity — a tight side passage, an earlier extension of uncertain planning status, an existing shed near the area cap — it is money well spent. It is what makes the unit financeable now and saleable later, because your solicitor will ask for evidence that the exemption genuinely applied.
Free indicative check
Answer eight questions. Your result appears immediately; no email address is required.
From survey to sign-off
Eco Sweethomes Properties Ltd is based in Dún Laoghaire, Co. Dublin. We work across Ireland, with site visits by appointment.
Design Certifier and Assigned Certifier duties on our projects are carried out by a Chartered Engineer registered with Engineers Ireland. That is the qualification the Building Control Regulations require for the person who inspects and certifies the works, and it is the reason we can take a garden dwelling from first survey through to the Certificate of Compliance on Completion without handing you off to a third party part way through.
We came to this work from fire engineering and Fire Cert applications. That background shows up in how we treat Part B on these units — means of escape, detection and fire-service access get a proper strategy rather than a box-tick, which matters more on a dwelling sitting at the far end of a garden than most people expect.
One team for the survey, the drawings, the structural design, the Building Control submissions and the sign-off.
The first site visit is free and carries no obligation. We will walk the garden with you, measure what needs measuring, and tell you on the day whether Class 3A is realistically available to you.
