45m² Planning Exemption Ireland

Ireland's planning rules for rear-garden buildings changed in July 2026. There are now two separate exemptions to understand, and they are not the same thing:

• The general garden-structure exemption (30 m²) — for a shed, store, home office or gym. This was increased from 25 m² to 30 m². The structure must be ancillary to the house and is not a dwelling.
• The Class 3A Detached Auxiliary Dwelling exemption (32–45 m²) — a new, time-limited exemption allowing a detached house in the rear garden of a principal house, between 32 m² and 45 m², without a full planning application. This is the exemption that can make a back-garden modular home possible without planning permission.

Both exemptions are subject to conditions. The 30 m² exemption covers general garden structures; the 32–45 m² Class 3A exemption covers a detached auxiliary dwelling. They are distinct, and the difference matters.

The long-standing exemption for a structure in the back garden — such as a shed, store, home office or gym — was increased from 25 m² to 30 m² under the 2026 regulations. This exemption applies to ancillary structures used in connection with the house, not to a self-contained dwelling.

A garden room or home office up to 30 m² at the rear of a house may qualify, provided it meets the conditions on height, position and use. The unit must be ancillary to the main dwelling — used by the household in connection with the house, not as a separate self-contained dwelling and not rented out independently.

The Class 3A exemption was introduced by the Planning and Development (Exempted Development (Act of 2000)) (No. 3) Regulations 2026 (S.I. No. 340 of 2026), signed on 16 July 2026 and coming into operation on 27 July 2026.

Under Class 3A, the construction, erection or placing of a detached house in the rear garden of a principal house may be exempt from planning permission, provided every statutory condition is met. The exemption is time-limited: it applies only to development commenced and completed between 27 July 2026 and 31 December 2030.

This is the exemption that can allow a modular home in your back garden without a full planning application — but it is not simply "modular homes up to 45 m² are exempt." It is a detached auxiliary dwelling, and it depends on the development meeting every one of the conditions set out in the Regulations.

The Class 3A exemption only applies where all of the statutory conditions are met. The principal conditions include:

• Floor area: the detached dwelling must be at least 32 m² and, taken together with other Class 3 structures in the rear garden, must not exceed 45 m².
• Ancillary occupancy: the dwelling may only be occupied in conjunction with the main dwelling house and cannot be sold or subdivided separate to the principal dwelling.
• Owner-occupier: the exemption applies only where the principal dwelling is the sole or main residence of the property owner at the time the development is commenced.
• No short-term letting: the detached dwelling may not be used for short-term letting.
• Height: no more than 4 m for a pitched or slated roof, or 3 m in any other case.
• Boundary setbacks: the structure must be at least 0.6 m from any wall or party boundary, and windows must be at least 0.6 m from the boundary they face.
• Private open space: the structure must not reduce the private open space reserved for the occupants to less than 25 m².
• No new road access: no new vehicular or pedestrian access onto a road may be constructed; independent pedestrian or wheelchair access within the curtilage is required.
• Services: there must be no separate connection to utilities (water or wastewater) — the dwelling is linked to the services of the principal house. Non-piped wastewater treatment must meet the EPA Code of Practice.
• Notification: you must notify the planning authority at least 14 days before commencement, including the location and Eircode.
• Building Regulations: full Building Control legislation (including Building Regulations and Fire Safety) continues to apply.
• Not temporary: the structure must not be temporary in nature (no caravan or mobile home).

This is general information, not planning advice. Every condition must be satisfied, and you should confirm your specific position with your local planning authority or a qualified planning professional before building. Source: S.I. No. 340 of 2026 and gov.ie Circular PLR-02 (17 July 2026).

A factory-built modular garden room or living pod may qualify for the 30 m² general exemption where it is an ancillary garden structure. A larger detached modular dwelling of 32–45 m² in the rear garden of a principal house may qualify for the Class 3A exemption, subject to all applicable conditions. Our garden rooms and smaller living pods are designed with these limits in mind, and our Chapter One two-bedroom home (38–45 m²) is sized to fit within the Class 3A range where site conditions allow.

If you want the building to be a self-contained dwelling used independently, sold separately, or used for short-term letting, the Class 3A exemption does not apply and you will likely need planning permission. See our granny flats guide for that distinction.

Under the 30 m² general exemption (ancillary, not a dwelling):

• A garden room or home office up to 30 m²
• A garden studio or hobby room
• A gym, therapy room or treatment room for personal use

Under the 32–45 m² Class 3A exemption (detached auxiliary dwelling):

• A detached auxiliary dwelling for a family member, occupied in conjunction with the main house
• A modular granny flat or ancillary living unit within the 32–45 m² range

Uses that go beyond ancillary occupancy — for example independent rental, short-term letting, or sale as a separate dwelling — fall outside the Class 3A exemption and generally require planning permission.

If your building qualifies for an exemption, you do not need to submit a planning application — but for the Class 3A exemption you must notify the planning authority at least 14 days before commencement, and you should keep documentation showing the building meets the conditions in case you sell the property later. If your building exceeds the exemption or its use falls outside it, we guide you through a full planning application as part of our turnkey service.

The information on this page is based on the official Irish planning legislation and government guidance:

• S.I. No. 340 of 2026 — Planning and Development (Exempted Development (Act of 2000)) (No. 3) Regulations 2026 (the Class 3A Detached Auxiliary Dwelling exemption), signed 16 July 2026, in operation 27 July 2026.
• gov.ie Circular PLR-02 — Department of Housing, Local Government and Heritage, published 17 July 2026.

Planning rules and conditions can change. This is general information, not planning advice — always confirm with your local planning authority or a planning professional before building.