StructuralEngineer.ie's summary: under the BCAR extension rules, an extension to a house with a floor area over 40 m² needs a Commencement Notice with compliance documentation, a designer and an assigned certifier, and a Certificate of Compliance on Completion. Since 2015, the owner of a domestic extension can instead lodge an opt-out declaration. The Building Regulations still apply either way.
BCAR is the Building Control (Amendment) Regulations, S.I. 9 of 2014, as amended in 2015. It added statutory certification to the existing commencement notice system for new houses and larger extensions.
When BCAR applies to an extension
| Extension | What’s needed |
|---|---|
| Exempt from planning, no Fire Safety Certificate | Usually no Commencement Notice |
| Needs planning, 40 m² or less | Commencement Notice (simple form) |
| Over 40 m² | Commencement Notice with compliance documentation, or with opt-out declaration |
“Total floor area” for an extension means the floor area of the extension itself, as described in the notice. Since July 2026, rear extensions up to 45 m² can be exempt from planning, which creates a 40–45 m² overlap. Confirm with your building control authority how they treat an exempt extension in that range.
The certified route
- Appoint a designer and an assigned certifier. A registered architect, registered building surveyor or Chartered Engineer.
- Lodge the Commencement Notice with design certificates, compliance documentation and an inspection plan, 14–28 days before starting.
- Inspections during construction, by the assigned certifier, following the plan.
- Certificate of Compliance on Completion, signed by the builder and the assigned certifier and lodged with the building control authority.
You end up with statutory certificates on the public register. That is the cleanest position when you sell.
The opt-out route
The owner lodges a Commencement Notice with a declaration of intention to opt out of statutory certification. No assigned certifier or completion certificate is required. But:
- The Building Regulations still apply in full
- Nobody is obliged to inspect, so evidence of compliance is up to you
- At sale, the buyer’s solicitor will still ask for evidence, typically an engineer’s or architect’s opinion of compliance. That is easiest to give if the engineer inspected during the work.
Which to choose
If the extension is over 40 m² and you plan to sell within a few years, or the build involves significant steel or foundation work, the certified route is usually worth it. If you opt out, still appoint an engineer to design it and inspect at foundation and steel stage, so an opinion of compliance can be given later.
Bottom line
Over 40 m², choose between statutory certification and opting out. Opting out removes the paperwork, not the regulations. StructuralEngineer.ie’s engineer is Chartered, so he can act as both designer and assigned certifier. Call 01 270 9764.
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Frequently asked questions
Who can be an assigned certifier?
A registered architect, a registered building surveyor or a Chartered Engineer, on the relevant statutory register. The same person can usually act as designer and assigned certifier on a domestic extension.
Does opting out save money?
It saves the statutory certification work, but the Building Regulations still apply in full. When you sell, the buyer's solicitor will want evidence of compliance. Without inspections during the works, that is harder and sometimes more expensive to provide.
When does the Commencement Notice have to go in?
Not more than 28 days and not less than 14 days before work starts, through the Building Control Management System.
Sources
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