The detail
The rules, the process and the questions.
Everything behind the one-page version — what S.I. 340 of 2026 actually requires, what quietly disqualifies a garden, and what we do about it.
S.I. No. 340 of 2026 · Class 3A
The exemption is real. It is also narrow, and it runs out.
On 27 July 2026 a new class of exempted development came into operation. It allows one permanent, detached auxiliary dwelling in the rear garden of a qualifying house without a planning application. It is not a relaxation of the rules — a project either satisfies every condition or it is unauthorised development. Building Regulations and Building Control are a separate question, and they apply in full.
Four conditions people rarely hear about.
No separate connection to utilities, including water or wastewater. Where there is on-site wastewater treatment, the structure must not encroach on the percolation area and the system must have capacity for the extra load under the EPA Code of Practice. Any windows must be at least 0.6 m from the boundary they face — a separate rule from the 0.6 m for the building itself. And the dwelling cannot be sold or subdivided away from the principal house.
The figure most people miss is the second one.
The 45 m² cap is cumulative across the curtilage, not a separate allowance for the new home. Every roofed structure already standing in the garden eats into it — and “roofed structure” is wider than most homeowners assume.
The cumulative cap
What disqualifies a garden is rarely its size.
The 45 m² ceiling is counted by roofed area in plan, and it includes open-sided cover. These all count against it. Most gardens we look at have three or four, and the owner has never thought of them as buildings.
Outside it, in their own classes: Barn Agricultural structure Polytunnel
No map can settle this. Somebody has to stand in the garden with a tape.
Aerial imagery will not reliably show a canopy over a back door, a covered side passage, or a pergola that has since been roofed. A desktop review is the right way to rule a property out cheaply and the wrong way to rule one in.
The second route — Class 1A
If the garden won’t take it, the house sometimes will.
The same 2026 package created a separate exemption for forming an additional dwelling inside an existing house. Where a rear garden fails on space, on the cumulative cap or on access, subdividing can still produce an independent, lettable unit — without a planning application and without touching the garden.
The broad shape, from S.I. 339 of 2026: subdivision may create no more than two units in total, each unit must be at least 32 m², and each must be self-contained rather than relying on shared internal space other than for access. Note that the two exemptions are mutually exclusive — Class 1A cannot be used where a Class 3A garden home has been built. Whether a particular house can do it turns on layout, means of escape, sound separation and services — a Building Regulations question before it is a planning one.
We screen both routes from the same Eircode, at no extra cost.
Names
Everyone has a word for it. None of them are in the regulation.
People come to us calling it a granny flat, an annexe, a pod, a cabin. Suppliers have a vocabulary of their own again. Every one of these describes something that could be a garden home — and something that could equally be a shed you are not allowed to sleep in.
Not one of those phrases appears in S.I. No. 340 of 2026. The regulation recognises a single thing: a permanent, detached dwelling in the rear garden of a principal house, meeting every condition it sets out.
The word on the brochure is not a compliance statement.
A building sold as a garden room and a building sold as a garden home can be the same building leaving the same factory. What separates them is whether it was designed, documented and certified for permanent residential occupation, and whether the garden it lands in satisfies the exemption. Neither question is answered by the name, the photography or the price. Ask instead who signs the compliance paperwork, and for what.
Building Regulations · Parts A to M
It is a planning exemption. Nothing else got easier.
Class 3A removes the planning application. It does not touch the Building Regulations, and a garden home is a new dwelling, so they apply in full — with the Building Control records to evidence it. The parts run A to M, with no Part I. Three of them decide most garden home layouts, and they are not the three people expect.
| Part | How it bites in a back garden |
|---|---|
| A · Structure | Foundation design on ground nobody has tested, and getting plant in to build it. |
| B · Fire safety | Decides layouts. Escape from a detached unit, separation from boundaries, and whether a fire appliance can reach it. The most common reason a garden home is redesigned. |
| C · Site preparation and moisture | Ground conditions, damp, and radon — which is assessed by area, not by building size. |
| D · Materials and workmanship | What the unit is actually made of, and who stands over it. |
| E · Sound | Rarely critical on a detached unit, but not nothing where boundaries are tight. |
| F · Ventilation | A small, airtight dwelling needs this designed rather than assumed. |
| G · Hygiene | Water supply and sanitary facilities in a building the regulation forbids from having its own separate connection. |
| H · Drainage and wastewater | Decides layouts. On an unsewered site the unit must not encroach on the percolation area, and the treatment system must have capacity for the extra load under the EPA Code of Practice. This closes more rural gardens than floor area ever does. |
| J · Heat-producing appliances | Flues, hearths and clearances if anything is burned. |
| K · Stairs, ramps and guarding | Level thresholds and any change in level on the approach. |
| L · Conservation of fuel and energy | Fabric, airtightness and services, and the Building Energy Rating that follows from them. |
| M · Access and use | Decides layouts. Approach to and use of the dwelling. Separately, the exemption itself requires independent pedestrian and wheelchair access from the road within your own boundary — which is why a mid-terrace with no side passage usually fails before anything is measured. |
Two separate hurdles, cleared by two separate people.
The exemption is satisfied by meeting the conditions in the regulation and serving notice on your planning authority. The Building Regulations are satisfied by design, construction and certification carried out by appropriately registered construction professionals. Passing the first tells you nothing about the second. Any company that presents them as one step has simplified something it should not have.
One chain, one team
From an Eircode to a certified home.
The common failure on these projects is not a bad builder. It is that nobody owns the whole chain: the supplier assumes the homeowner arranged certification, the homeowner assumes the supplier did, and the gap surfaces years later when a solicitor asks for the file.
Check
Send an Eircode. We tell you whether it’s worth going further. Free.
Survey & design
We measure the garden on site, then draw and specify the home to meet the conditions.
Notices
We lodge the exemption notice with the planning authority, and the Commencement Notice on BCMS with your Assigned Certifier and builder named.
Build & certify
Your builder delivers and manages the build. Our Assigned Certifier inspects each stage, signs it off and registers the completion certificate. You get the full file.
What it costs
The first check is free.
Send us the Eircode and we’ll tell you whether the garden is worth taking further, at no cost and with no obligation. If it is, we’ll explain what the next stage involves and what it costs before you commit to anything.
The building itself is priced by the manufacturer or builder who supplies it. We do not publish a build-cost figure we cannot stand over for your particular site.
Before you commit
Questions worth asking any garden home company.
| The question | Our answer |
|---|---|
| What can you build? | Modular, timber frame or blockwork. We measure the site first, explain what each route means for it, and you choose. |
| Who builds it? | Proven manufacturers and builders we place you with. They deliver and manage the build; we stay in touch with it. |
| Is the 45 m² cap cumulative? | Yes. Measured on site, structure by structure, including awnings and covered areas. |
| What if the garden fails? | We screen the Class 1A route inside the house from the same address. |
| Who certifies compliance? | Our registered building surveyor, as your Assigned Certifier: Commencement Notice before work starts, inspections during the build, completion certificate registered before anyone moves in. |
| What do you hand over? | A building and the complete file — drawings, notice, specifications, certificates, energy rating, test and service records. |
Why the paperwork is the asset
An uncertified home in the garden is a liability with a roof on it.
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Occupancy
Under the exemption the dwelling is tied to the house in front of it: occupied in conjunction with the main house, not sold or subdivided away, and no short-term letting. If you want a home you can let to a tenant, that is a planning application rather than the exemption — a different route to the same building, and one we handle.
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Finance
Lenders make their own decisions and nobody can promise an outcome. What is within our control is that the file exists and is complete, so the question a lender asks has an answer.
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Insurance
Cover turns on disclosure, use and compliance. Insurers can decline or dispute a claim where a structure was not disclosed or was not built to the applicable standards.
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Sale
A purchaser’s solicitor will requisition the planning and compliance position on everything on the site. Missing records delay closings, reduce offers and occasionally collapse sales.
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Enforcement
Where a condition is not met, the development is unauthorised. Enforcement can require alteration, cessation of use or removal, and retention is never automatic. Expect councils to take a close interest while this class is new.
Context
The shortage is real. Your garden is still a separate question.
That is the policy reasoning behind a route that lets one extra home go into an existing garden, on existing services, inside an established community, without a planning application. It is a serious piece of regulation and it will produce real homes.
None of it makes your garden suitable. A national shortage is not evidence about one plot, and the conditions are applied to the plot, not to the argument for it. We would rather tell you no in a week than sell you a yes and leave you to discover the percolation area.
Questions
The ones homeowners ask first.
What exactly changed in July 2026?
A new class of exempted development came into operation on 27 July 2026 under S.I. No. 340 of 2026. It permits one permanent, detached auxiliary dwelling in the rear garden of a qualifying principal house without a planning application, subject to detailed conditions covering ownership and occupation, planning history, floor area, existing structures in the curtilage, retained open space, height, boundary separation, access, services, use and prior notification of the planning authority. Building Regulations obligations are unaffected and apply in full.
Do I need a certifier for a garden home?
Yes. A garden home is a new dwelling, so Building Control applies in full even though no planning application is needed. Before work starts, a Commencement Notice with full documentation goes to the council through BCMS, naming an Assigned Certifier and a builder. The certifier inspects during the build, and a completion certificate signed by the builder and the certifier has to be registered by the council before anyone moves in. That is separate from the 14-day notice to the planning authority. Our registered building surveyor acts as Assigned Certifier on the homes we arrange, so it is in place from the start.
Does a big garden mean I qualify?
No, and this is the most common misunderstanding. Garden area is one condition among many. We regularly see generous gardens fail on the cumulative 45 m² cap because of structures already standing in them, on the 0.6 m boundary separation once a workable footprint is set out, or on independent access. Equally, modest gardens sometimes pass. The only way to know is to measure.
Which is better — modular, timber frame or blockwork?
All three are available and the choice is yours. None of them is better in the abstract:
- Modular where speed and programme certainty matter most. Units can be craned in, or flat-packed and brought through the side passage where access is tight — so a narrow garden does not rule modular out.
- Timber frame where you want the plan shaped around an awkward plot, built up by hand on site.
- Blockwork where you intend to hold the property long term and want the construction type lenders, valuers and buyers treat as conventional.
We work with manufacturers across all three, so there is no route we need to talk you into.
What will it cost to build?
We do not publish a headline figure, because a number quoted before anyone has seen your ground conditions, access and service runs is not information — it is a guess with a euro sign on it. We put your specification to our panel across all three routes and bring you real quotations. When you compare them, check what each includes: surveys, design, certification, Building Control work, foundations, transport and cranage, utility connections, drainage, kitchen, bathroom, heating, energy measures, landscaping, VAT and contingency.
Can I rent it out?
Yes, but not under the exemption. Class 3A provides that the dwelling “may only be occupied in conjunction with the main dwelling house and cannot be sold or subdivided separate to the principal dwelling”, and short-term letting is ruled out outright. That is the price of skipping the planning application — the State gave away the application in return for the home staying tied to the house.
If letting is the point, the route is a full planning application instead. There is more on what the exemption allows on occupancy, quoting the regulation itself. Longer, dearer, and never guaranteed — overlooking, separation, access and your council’s own policy all bear on it — but what it delivers is an independent home that is yours to let. Tell us at the outset that income is the aim and we will tell you early whether your site is likely to carry a permission, before you spend on a design. Tax on any money that changes hands is between you and your accountant.
Will it be A-rated?
Not automatically, and be wary of anyone who says otherwise before the design exists. A new dwelling must address Part L and will require a Building Energy Rating where applicable, but the final rating comes out of the complete design and the verified construction. It should be modelled and specified for your project, not claimed from a brochure.
Are all products sold as “garden homes” compliant?
No. Many structures marketed with that language were designed as garden offices, studios or leisure rooms and were never documented for permanent residential occupation. Appearance and price establish nothing. Before you buy, ask in writing who is responsible for the Irish project design, the Building Control process, the site-specific foundation and services, the inspections and testing, and the completion documentation — and get names and registrations, not reassurance.
What if my garden doesn’t qualify?
We tell you in the free check, and we don’t charge you to find out. We then look at whether the Class 1A route inside the existing house is open — forming an additional dwelling by subdivision, subject to its own conditions. If neither route works we will say that too.
Is there a deadline?
Yes. Qualifying development must be both commenced and completed by 31 December 2030. That sounds distant until you count backwards through survey, design, procurement, the statutory fourteen days’ notice, groundworks, delivery or erection, fit-out and certification.
Will it overlook the neighbours, or they me?
Privacy is settled at layout stage or not at all, and part of it is not a matter of taste. The exemption requires any window to be at least 0.6 m from the boundary it faces — a separate condition from the 0.6 m the building itself must stand off. Miss it and the unit is unauthorised, however well it is finished.
Beyond that it is design. Orientation of the main windows, where the door and the path go, obscure glazing where a window has to face the wrong way, boundary treatment and planting. All of it has to be reconciled with daylight, escape in a fire, and access — which is why it belongs in the siting drawing rather than in a conversation about blinds after delivery.
Can I claim Rent-a-Room relief on it?
Budget 2027 (6 October 2026) announced that Rent-a-Room relief will cover new garden homes of 32 to 45 m² built under the exemption, with a tax-free limit of €16,000 a year from 1 January 2027. It still has to pass in the Finance Act, so treat it as announced, not yet law, and check with Revenue or your accountant before you count on it. More on Rent-a-Room relief for garden homes →
There is a prior question in any case. Class 3A provides that the dwelling may only be occupied in conjunction with the main dwelling house, and rules out short-term letting outright. We treat the position on letting to a third party as genuinely open rather than settled, and we say so. Anyone publishing a worked rental return under the exemption has taken a view on that question without telling you they have taken one. If income is the object, a planning application is the honest route to it.
Is any of this still uncertain?
Some of it is, and we would rather say so. A small number of conditions have not yet been tested in practice or clarified in guidance — among them how the rules apply to certain house types, where the retained open space must sit, and the treatment of letting. Where a point is genuinely open, our reports tell you which way we read it, what the exposure is if the other reading prevails, and who has to answer it. We do not record an unknown as a pass.