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Can I Put a Modular Home in the Back Garden?

A common question right now, and the answer changed on 27 July 2026. Here is the position today and the conditions that come with it.

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The rules changed on 27 July 2026. A detached garden dwelling of 32–45 m² is now exempted development, subject to conditions, including a duty to notify the planning authority at least 14 days before work starts. This is general information, not formal advice, check with us before you order a unit.

The Position Today

Since 27 July 2026 a detached, self-contained dwelling in your back garden can be exempted development. S.I. 340 of 2026 inserted a new Class 3A covering an auxiliary habitable dwelling of between 32 m² and 45 m², linked to the services of the principal house. Separately, a garden room used as ancillary space (home office, gym, studio) now falls within a 30 m² limit, raised from 25 m², subject to height and open-space conditions. See the exemption checker for the full set.

In force  What changed on 27 July 2026 (S.I. 338 to 344 of 2026). You no longer need permission to:
  • › Add a detached home in your back garden of 32–45 m², linked to the services of the main house and meeting all building and fire regulations.
  • › Divide your home into a separate self-contained unit of at least 32 m².
  • › Extend your home by up to 45 m² (was 40 m²), and add a garden structure up to 30 m² (was 25 m²).

Two conditions do the real work, and both are easy to miss. The garden dwelling and the sub-division each require you to notify the planning authority at least 14 days before work starts, that is a condition of the exemption, not a courtesy, and building first may mean you never had the exemption at all. The Class 3A exemption is also time-limited, currently to 31 December 2030.

Exempt from Planning Is Not Exempt from Everything

  • › Building & fire regulations still apply. Exemption from planning is not exemption from Building Regulations, a habitable unit must meet them in full.
  • › Services and drainage. Water, wastewater and connections need to be dealt with properly.
  • › Protected structures & conservation areas typically fall outside these exemptions.
  • › Renting it out or separating it in title can raise further planning and legal questions.
Our take. The exemption is real, but it is not a free pass. The 14-day notification is the condition most likely to be overlooked, and a habitable 32–45 m² unit has to meet the Building Regulations in full, a materially higher bar than a garden room. Where a site is tight, overlooked, or in a conservation area, an application may still be the safer route. Talk to us.
Sources: Citizens Information, altering your house · gov.ie, new exemptions in effect (27 July 2026) · S.I. 340 of 2026
Reviewed 1 August 2026.

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