Garden room planning: Class 3 versus Class 3A

Start with the intended use, not the label “garden room”. A home office or hobby space is different from accommodation for someone to live or sleep in. A small building does not become a lawful dwelling just because it has insulation, plumbing or an attractive layout.

Class 3 is for non-habitable garden structures

Class 3 covers non-habitable garden structures totalling no more than 30 m², subject to its conditions; it does not authorise living or sleeping accommodation. Department Circular PLR 02/2026.

The 25 m² Garden Studio is Nua Living’s garden room or home-office product. Its product size is not the statutory cap. The Department circular confirms the current Class 3 total of 30 m²; older advice using 25 m² as the legal cap predates the change.

Class 3A is a distinct dwelling route

Condition 7 of Class 3A sets a 32–45 m² external-footprint band, counted together with earlier Class 3 garden structures. S.I. No. 340/2026, Class 3A.

The exemption covers a qualifying detached house in the rear garden, subject to all the conditions. The main house’s occupation, access, remaining garden, services and existing structures matter. See the full Class 3A planning guide; satisfying an area rule alone is insufficient.

Neither class chooses a construction material for you

Planning use does not establish whether the structure must use timber, concrete or steel, or select its foundation system. The Department’s auxiliary dwelling Information Note, Part D discusses several construction methods. Appropriate foundations, compliance evidence and specification follow from the design and site.

Nua Living uses ICF, with reinforced concrete poured on site between permanent insulation layers. That is our construction method, not a reason to describe other materials as inherently temporary. Read about the ICF build separately from planning eligibility.

A dwelling needs its own compliance process

Conditions 16–18 require notification to the planning authority at least 14 days before work starts; the notification records use of the exemption and is not planning approval. S.I. No. 340/2026, Class 3A.

A Class 3A auxiliary dwelling follows the normal Building Control process, including a Commencement Notice, design and assigned certifiers, a competent builder and a Certificate of Compliance on Completion. Department Circular BC07-2026.

The planning notification and Building Control submission are separate. Lodge the BCMS Commencement Notice 14–28 days before starting work; allow at least 14 days after the council notification too. Start with the BCMS submission, then the council notification, so the periods can run together. Check the pre-start paperwork guide for current council forms and professional responsibilities.

Can you live or sleep in a garden room?

A Class 3 office or hobby building is not the route for living or sleeping accommodation. Describe the intended use before choosing the product. If accommodation is proposed, investigate the dwelling route and its full conditions with your planning adviser.

Describe the intended living and sleeping arrangements at the outset. Do not buy an office building and assume that a change of furniture settles the planning and Building Control questions. Compare the dwelling options and obtain site-specific advice before proceeding.

Discuss your garden

Tell us whether you need an office or a dwelling, and what garden structures already exist. Request a callback and a free, no-obligation site visit. We can discuss site eligibility and prepare a written scope and quote.