The 45 m² garden dwelling planning exemption (Class 3A)
Since 27 July 2026, S.I. No. 340 of 2026 (Class 3A) allows homeowners in Ireland to build a detached habitable dwelling of 32 m² to 45 m² in the rear garden without planning permission — subject to a 45 m² cap across all garden structures, owner-occupation of the main house, 14 days prior written notice to the council, full Building Regulations compliance, and completion by 31 December 2030.
Every condition of the 27 July 2026 Class 3A habitable garden dwelling exemption, and how it differs from the 30 m² Class 3 garden room rule.
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Configure your size, cost and planning exemption
Pick your floor area, specification and use. Shows our 13.5% VAT price guide and whether your build falls under Class 3 (up to 30 m² non-habitable) or Class 3A (32 to 45 m² habitable garden dwelling, S.I. No. 340 of 2026).
Guide price (incl. 13.5% VAT) & planning status
€108,000 to €144,000
Class 3A Exempt (45 m² within 32–45 m² band)
Based on 45 m² at our turnkey habitable unit guide rate of €2,400 to €3,200 a m² (including 13.5% VAT on supply and installation). Exempt from planning permission under Class 3A (S.I. No. 340 of 2026, in force 27 July 2026): a detached habitable dwelling of 32 to 45 m² in the rear garden. Total garden structures cannot exceed 45 m², the homeowner must live in the main house, it connects to the main house's services, cannot be sold separately or short-term let, requires 14 days prior written notification (with Eircode) to the council, must meet Building Regulations, and must be completed by 31 December 2030.
Send this for a written quoteClass 3 (30 m²) vs Class 3A (32 to 45 m²) side by side
The July 2026 planning regulations (S.I. Nos. 338 to 344 of 2026, signed 16 July 2026 and in force from 27 July 2026) created two separate exemptions for detached buildings in a back garden. Mixing them up is the most common mistake:
| Rule | Class 3: Garden room / office (S.I. 338 of 2026) | Class 3A: Habitable garden dwelling (S.I. 340 of 2026) |
|---|---|---|
| Permitted use | Non-habitable only (home office, gym, studio, playroom, shed — no sleeping) | Habitable dwelling (1 to 2 bed granny flat / independent living unit with kitchen & bathroom) |
| Floor area allowed | Up to 30 m² (increased from 25 m² on 27 July 2026) | 32 m² to 45 m² (minimum 32 m², maximum 45 m²) |
| Combined garden structures cap | 30 m² total across all Class 3 structures | 45 m² total when combined with any other garden structures |
| Where it can sit | Behind the front wall of the house | In the rear garden only |
| Who must live in the main house | Normal householder rules | The homeowner must reside in the main house |
| Separate sale or letting | Part of the house | Cannot be sold or let separately from the main house; no short-term letting |
| Services | Power from the house | Must be connected to the main house's services (water, drainage, electricity) |
| Council notification | None required (optional €80 Section 5 declaration) | 14-day prior written notification to your local council (including Eircode) before starting |
| Sunset deadline | Permanent class | Works must be commenced and completed by 31 December 2030 |
Checklist before you order a 32 to 45 m² Class 3A unit
- Floor area between 32 m² and 45 m². A unit under 32 m² cannot use Class 3A for sleeping, and a unit over 45 m² needs full planning permission.
- Total garden structures ≤ 45 m². If you already have a 10 m² shed in the back garden, either remove the shed or keep the new Class 3A dwelling to 35 m² so the combined footprint stays within 45 m².
- Owner-occupied main house. You must own and live in the principal house; either the family member/occupant lives in the garden dwelling or you move into the garden dwelling while family live in the main house.
- No short-term or separate commercial letting. The unit is ancillary to the main house and cannot be put on short-term holiday rental platforms or sold as a separate title.
- 14-day council prior notification. At least 14 days before groundworks begin, submit the statutory prior notification form (with the main house's Eircode and site layout) to your local planning authority.
- Building Regulations still apply in full. Exempted development only exempts you from planning permission — the dwelling must still meet Building Regulations (Part B fire safety, Part F ventilation, Part L energy/U-values, Part M access).
- Protected structures & ACAs. If the house is a Protected Structure or inside an Architectural Conservation Area, check with the council or request an €80 Section 5 declaration before ordering.
- Complete by 31 December 2030. Class 3A is a time-limited housing measure; works must be finished by 31 December 2030.
What modular buildings cost in Ireland
Our price guide by size and specification, including 13.5% VAT on supply and installation.
| Job | Typical cost | What moves the price |
|---|---|---|
| Insulated garden office or studio, 12 to 16 m² (Class 3) | €18,000 to €32,000 | Cladding, glazing, base and cable run from the house |
| Large garden room or gym, 20 to 30 m² (Class 3 max) | €28,000 to €55,000 | Up to the 30 m² non-habitable exemption limit; no plumbing or kitchen |
| Class 3A habitable garden dwelling, 32 to 37 m² (1-bed) | €65,000 to €105,000 | Kitchen, shower room, Building Regs insulation, base and service hook-ups |
| Class 3A maximum garden dwelling, 40 to 45 m² (1 to 2 bed) | €80,000 to €135,000 | Largest exempt rear-garden unit (45 m² total garden structures cap) |
| Standalone 2 to 3 bed modular home, 75 to 85 m² | €175,000 to €255,000 | Full planning permission, BCAR, foundations and site services |
| Factory shell only (weathertight exterior), per m² | €1,200 to €1,800 a m² | Excludes groundworks, internal plumbing/kitchen and service connections |
| Insulated & fitted garden room rate, per m² | €1,600 to €2,400 a m² | Includes 13.5% VAT when supplied and installed by the builder |
| Turnkey habitable modular home rate, per m² | €2,400 to €3,200 a m² | All-in with kitchen, bathroom, foundations and 13.5% VAT |
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Questions people ask
Why can't I build a 25 m² granny flat to sleep in without planning permission?
Because Class 3 (up to 30 m²) strictly prohibits human habitation, and Class 3A (the habitable garden dwelling exemption) sets a minimum floor area of 32 m² alongside Ireland's minimum studio/1-bed apartment size standards. To be exempt as a habitable dwelling, the footprint must be 32 m² to 45 m².
What is a Section 5 declaration and should I get one?
A Section 5 declaration is an official written ruling from your county or city council confirming that your proposed build is exempted development. It costs €80 and the council is due to issue its decision within 4 weeks — useful peace of mind for your solicitor if you ever sell the property.
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