BCMS and Class 3A: the two pre-start processes

A planning exemption does not remove the Building Control process for a new garden dwelling. Keep two records in your project file: the council’s Class 3A planning notification and the Commencement Notice with compliance documents on BCMS. Their dates and purposes differ.

Two processes, different purposes

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.

A practical timeline

1. Confirm the proposed site, use and design against the full exemption conditions. Identify the certifiers and builder before setting a start date.
2. Lodge the BCMS submission and retain its reference. Send the planning notification with the owner’s declaration and the council’s supporting information.
3. Check validation and both notice periods before starting. If the BCMS start window expires, arrange a new notice before work.
4. At completion, have the Certificate of Compliance on Completion registered before occupation.

The Department’s auxiliary dwelling Information Note, section 3, explains the BCMS window and completion requirement. A lodged notice alone does not prove that completed construction complies.

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.

Does the exemption apply to your design?

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 size band is only one condition. Access, existing structures, remaining garden, services and occupation also matter. The planning guide explains the full set; the professional assessment must address your site, not just a model’s advertised area.

What Nua Living organises

We prepare and lodge both pre-start submissions; you sign as owner. Ask the team to identify the design certifier, assigned certifier and builder, and to set out professional fees in the written quote. Use the build journey to see where paperwork fits.

Primestructures carries out the on-site ICF structural build in 5–10 days once foundations are ready. This is a structural stage, not a move-in promise: design, site preparation, statutory processes, fit-out and service connections need their own programme.

Discuss your garden

Bring your proposed layout, site access information and any existing garden structures to the discussion. Request a callback and a free, no-obligation site visit. We can discuss site eligibility and prepare a written scope and quote.