How to Build a Granny Flat in a Dublin Garden: Rules, Costs & Sizes

Building a granny flat in a Dublin garden requires a rear space that leaves at least 25 m² of private open area for the main house. Under S.I. No. 340/2026, units up to 45 m² are exempt from planning permission if they have a separate entrance and the owner lives in the main property.

How much space do I need for a granny flat in a Dublin garden?

You need enough space to fit the footprint of the flat while leaving a minimum of 25 m² of private rear garden for the main house. Dublin gardens vary widely in size and shape, from long, narrow plots to wider suburban spaces. The planning exemption rules dictate that the new unit must sit entirely in the rear garden. You cannot build it to the side or front of your property without applying for full planning permission.

Before deciding on a size, measure your available rear space. You must account for the external footprint of the building and the mandatory 25 m² of remaining garden. Nua Living offers four fixed-price sizes to suit different garden capacities.

Unit Size	Description	Base Price (+ VAT at 13.5%)
25 m²	Studio Flat	€69,000
33 m²	1 Bed Granny Flat	€93,900
45 m²	1-or-2 Bed Granny Flat	€126,500
48 m²	2 Bed Granny Flat	€134,500

These fixed prices include design, build, and full project management. They exclude site works, connections, and professional fees.

Do I need planning permission for a garden flat in Dublin?

You do not need planning permission if your detached garden dwelling is 45 m² or smaller and meets specific conditions under S.I. No. 340/2026. This exemption takes effect on 27 July 2026 and currently runs until 31 December 2030.

To qualify for the exemption, your project must meet these exact criteria:

• The unit must be located in the rear garden of the main home.
• At least 25 m² of private garden space must remain after construction.
• The unit must have a separate entrance.
• The owner of the property must live in the principal dwelling.

The requirement for a separate entrance means the occupant of the flat must be able to access their home without walking through the main house. In most Dublin properties, you achieve this via a side gate or a rear laneway. The rule stating the owner must live in the principal dwelling prevents property investors from buying suburban homes solely to fill the gardens with rental units.

If you want to build our 48 m² 2 Bed Granny Flat, you will need to apply for full planning permission because it exceeds the 45 m² limit. You can read more about the regulations in our planning guide. Remember that while planning permission might be exempt, Building Control, fire safety, and BER rules still apply in full.

How is an ICF granny flat built in a back garden?

We build the structure on-site using ICF (Insulated Concrete Formwork), pouring a reinforced concrete core between two permanent layers of insulation. This is not a timber-frame or steel-frame pod, and it is not delivered fully assembled on a lorry.

Access to Dublin rear gardens is often restricted by narrow side passages or terraced layouts. Because we use ICF construction, we bring the materials through standard access points and build the walls in place. We stack hollow insulation blocks to form the shape of your walls, place steel reinforcement inside, and pump concrete into the core. The insulation remains in place permanently.

The on-site structural build takes 5–10 days once the foundations are ready. Design, planning, and utility connections add lead-time before the structural work begins. The resulting building is highly insulated and airtight. Ireland's nZEB minimum standard is BER A2, but Nua Living homes are designed to reach BER A1–A0. The concrete core also provides excellent soundproofing, which is highly practical in built-up residential areas.

What are the costs to build a granny flat in Dublin?

Nua Living offers four fixed-price sizes starting at €69,000 plus VAT at 13.5% for a 25 m² studio, excluding site works, connections, and professional fees. We manage the design, build, and full project management for these units.

The fixed prices for our granny flats cover the building itself. You must budget separately for groundworks, connecting electricity and plumbing to the main house or street, and any professional fees required for certification or planning applications. Digging trenches for water and waste pipes in an established garden requires careful planning, which we assess during our initial visit.

Frequently Asked Questions

Can I build a 48 m² granny flat without planning permission?

No. Under S.I. No. 340/2026, the planning exemption is strictly capped at 45 m². A 48 m² granny flat requires full planning permission.

How long does it take to build the granny flat in my garden?

The on-site structural build takes 5–10 days once the foundations are ready. Design, planning, and utility connections will add lead-time before the structural work begins.

How do you get the materials into a terraced Dublin garden?

We use ICF (Insulated Concrete Formwork), which means we build the structure on-site rather than delivering a pre-built unit on a lorry. The materials can be carried through standard side access or narrow passages.

Does the granny flat need its own BER certificate?

Yes. Building Control rules apply in full, and the unit must meet Ireland's nZEB minimum of BER A2. Nua Living homes are designed to reach BER A1–A0.

Ready to check your garden?

We always recommend a free, no-obligation site visit as the best way to confirm your planning eligibility and get a fixed quote. We can measure your rear garden, check your side access, and explain the site works required. Check if your garden qualifies and get a fixed price.