Granny Flats in Ireland: Planning Rules, Sizes and Costs (2026 Guide)
For years, building a granny flat in your back garden meant a full planning application, months of waiting and a real chance of refusal. That changed on 27 July 2026. Under the new exempted development regulations, a self-contained garden dwelling of between 32m² and 45m² can now be built behind your home without planning permission, provided you meet a set of conditions.
One thing up front: planning exempt is not rules exempt. A granny flat is a home. It has to meet Building Regulations in full, be notified to your council, and be built to a standard a garden office never needs. Garden Office Solutions designs and builds to that standard, and this guide sets out what the new rules allow, what they do not, and what it costs.
What Counts as a Granny Flat?
A granny flat, also called a garden annex, garden dwelling or back garden home, is a self-contained living space in the garden of a main house. It has its own bedroom, bathroom and kitchen, and someone lives in it full time. That is what separates it from a garden room, which is ancillary space with no sleeping accommodation and nobody living in it. Garden rooms have their own exemption, now up to 30m², covered in our post on 30m² planning-exempt garden rooms.
The same three groups build them:
- Parents moving closer to family without moving in
- Adult children who need a front door of their own
- A live-in carer, or a self-contained guest annex
A granny flat falls under a separate, newer exemption with tighter conditions than a garden room, and it is built as a dwelling from the foundations up. If your project does not fit inside those conditions, larger than 45m², two storeys, or a site with a small garden, then it is not exempt and you are back to a standard planning application. That is still very doable, and we guide clients through it, but budget for the time.
The 2026 Planning Exemption in Plain English
The regulations that took effect on 27 July 2026 added a new class of exempted development for a single-storey dwelling unit in the rear garden of a house. The headline conditions are:
- Size. At least 32m² and no more than 45m². The combined footprint of the granny flat and any other sheds or outbuildings cannot exceed 45m², so an existing 12m² shed caps your granny flat at 33m².
- Height. Single storey only. Up to 4m for a pitched, slated or tiled roof, or 3m for any other roof type.
- Where it goes. Rear garden only, at least 0.6m from any wall or boundary, with at least 25m² of private open space left over.
- Access and services. Its own pedestrian and, where relevant, wheelchair access within the site. No new road entrance. Water, drainage and electricity connect to the main house.
- Occupancy. The main house must be your principal private residence. The annex is occupied in conjunction with it and cannot be sold or subdivided separately. Short-term letting is prohibited.
- Notification. You must notify your local authority at least 14 days before works begin. It is a notification, not an application, but skipping it puts you outside the exemption.
- Time limit. The exemption covers developments commenced and completed between 27 July 2026 and 31 December 2030.
Caravans, mobile homes and other temporary structures do not qualify. Protected structures and homes with restrictive covenants in their title deeds may still be caught by other rules even where planning is exempt. For a wider look at what changed this year, read New Planning Rules 2026; for the older rules that still apply to cabins and log cabins, see Do You Need Planning Permission? Confirm the detail with your local authority or a planning consultant before you commit.
Building Regulations: The Part People Forget
A garden office is a shed with good insulation. A granny flat is a dwelling, and the law treats it as one. Planning exemption does nothing to remove the Building Regulations, which apply in full. In practice that means:
- Fire safety. Separation distance from the main house and boundaries, fire-rated construction where required, smoke and heat detection, and a compliant escape route.
- Structure and foundations. A properly engineered base, not a shed base.
- Thermal performance. The dwelling has to meet the energy standards for new residential units. Our SIP panel construction is BER A-rated as standard, so this is where the build spec earns its keep. See how we insulate for year-round use.
- Ventilation and drainage. Mechanical ventilation in the bathroom and kitchen, and a drainage connection that your engineer signs off on.
- Accessibility. Level access, door widths and a bathroom layout that suits the person who will actually live there. If it is for a parent in their seventies, design it for a parent in their eighties.
- Certification. Depending on how your local authority treats the notification, you may need a Commencement Notice and a Certificate of Compliance on completion. Ask early.
None of this is a reason not to build. It is the reason to build with someone who has done it before.
Sizes and Layouts That Work
The 32m² floor means the smallest compliant granny flat is already bigger than our largest standard garden room. That is deliberate: the rules are designed to produce a proper home, not a converted shed.
- 32–35m² — open-plan living and kitchen, one double bedroom, wet room. Suits one person, a parent or a live-in carer.
- 36–40m² — living and kitchen, one bedroom, bathroom, plus utility or storage. Suits a couple, or an adult child working from home.
- 41–45m² — living and kitchen, one large or two small bedrooms, bathroom and hall. Suits a couple with a spare room or home office.
Two design notes from experience. First, put the bedroom on the side away from the main house so both households keep their privacy. Second, spend money on the bathroom: a level-access wet room with a wall-hung basin costs little more than a standard bathroom and will keep the annex usable for decades. Every build uses the same construction as our garden rooms, Canadian red cedar cladding, structural insulated panels, triple-glazed windows and doors, and a BER A rating. You can see the finish in our project gallery.
What Does a Granny Flat Cost in Ireland?
Our standard garden rooms are priced from €19,950 for 12.5m² up to €43,600 for 26.4m², fully finished and installed, which works out at roughly €1,500 to €1,650 per square metre. A granny flat starts from the same construction, so at 32m² to 45m² that puts the structure itself in the region of €48,000 to €74,000. Full details are on our garden room cost page.
On top of that, a dwelling needs things a garden room does not: a kitchen, a bathroom, plumbing and drainage connections, fire-rated construction, an engineered foundation and certification. How much those add depends on your site, how far the services have to run and the kitchen and bathroom specification you choose. That is a guide, not a quote. We survey the site, check the services and give you a fixed price before anything is ordered. Finance is available.
Compare that with what it replaces: a house extension of similar size in Dublin now routinely runs well past €100,000, as our extension cost guide sets out, and it does not give your parent or your adult child a front door of their own. A well-built, compliant annex also adds usable accommodation that buyers increasingly look for, which we covered in Does a Garden Room Add Value to Your Home? One caveat: because the annex cannot be sold separately, its value is realised as part of the main house, not as a standalone asset.
How the Process Works with Garden Office Solutions
- Site visit and feasibility. We measure the garden, check the 45m² and 25m² limits against what is already there, look at where the services run and confirm the project fits the exemption. If it does not, we tell you what a planning application would involve.
- Design. Layout, elevations and specification, drawn up to Building Regulations standard so your engineer and the council have what they need.
- Notification and certification. We help you prepare the 14-day notification to the local authority and coordinate the structural and compliance sign-offs.
- Build. Groundworks and service connections first, then the SIP structure goes up fast. Because the panels are manufactured off-site, the disruption to your garden and your neighbours is measured in days, not months.
- Handover. Fully finished, connected, certified and ready to move into.
Our five-day garden room build is not the timeline for a granny flat, because of the groundworks, plumbing and certification. The same approach applies, though: as much as possible done in the factory, as little as possible done in your garden.
Frequently Asked Questions
Not since 27 July 2026, provided the dwelling is 32m² to 45m², single storey, in the rear garden, meets the height, boundary, access and open-space conditions, and you notify the council at least 14 days before starting. Outside those conditions, yes, you need planning permission.
Not under the garden room exemption. Garden rooms up to 30m² are exempt as ancillary space only; sleeping accommodation and independent living are excluded. To live in a garden building it has to be built and notified as a dwelling under the new granny flat exemption, or have full planning permission.
Yes. The combined floor area of the new dwelling and all other structures in the garden cannot exceed 45m². Removing an old shed is often the simplest way to free up the allowance.
Short-term letting is explicitly excluded under the exemption, so no Airbnb. Longer-term arrangements are less clear-cut and depend on the "occupied in conjunction with the main dwelling" condition and how your council interprets it. If renting to a non-family member is part of your plan, get written advice before you build, not after. We go into this in more detail in Live In or Rent Out a Garden Room.
No. It cannot be sold or subdivided from the main house.
No. The exemption is for the rear garden only.
No. The regulations expect the dwelling to use the same connections as the main house. Your electrician and plumber will run sub-mains and drainage from the existing supply.
Allow for design, notification, groundworks, the build and certification. The structure itself goes up in days; the whole project, from first visit to handover, is typically a few months rather than the year-plus a traditional extension can take.
The current exemption covers developments started and finished by that date. Anything after that will depend on whether the government extends or replaces the regulations.
Thinking About a Granny Flat?
If you have a parent, an adult child or a carer who needs a home of their own and you have a rear garden, 2026 is the first year this has been possible without a planning battle. Get in touch or call 083 811 9134 and we will tell you, honestly, whether your garden fits the rules and what it would cost.
This article is general guidance based on the regulations that took effect on 27 July 2026. It is not legal or planning advice. Confirm the requirements with your local authority before committing to any build.