StructuralEngineer.ie's summary of published 2026 Irish cost guides: extension engineer fees are typically €1,200–€2,200 for a single-storey rear extension and €2,000–€3,500 for a two-storey or wraparound extension. Complex jobs with site investigation can reach €5,000. BCAR certification over 40 m² is usually priced on top.
The engineer’s fee is a small part of an extension budget. Published 2026 figures put building costs at roughly €1,900–€3,400 per m². But the design decides how much concrete and steel the builder puts in, and whether the extension can be certified when you sell.
Typical fees at a glance
| Extension | Typical engineering fee |
|---|---|
| Single-storey rear | €1,200–€2,200 |
| Single-storey, larger or with wide glazing | €1,500–€3,000 |
| Two-storey or wraparound | €2,000–€3,500 |
| Complex, with site investigation | €2,500–€5,000 |
| BCAR designer and assigned certifier (over 40 m²) | Priced separately |
What the fee should include
- Site visit to check the ground, drains, trees and the rear wall
- Foundation design to I.S. EN 1997-1
- Steel for the opening into the house: beam, posts or goalpost
- Roof and floor structure, rooflight trimming
- Drawings, calcs and a steel schedule your builder can price
- Inspections of foundations and steel before they are covered
- An opinion of compliance, or BCAR certificates over 40 m²
What moves the fee
- Ground. Trees on clay, made ground or a drain under the footprint mean deeper or different foundations and possibly trial holes
- Opening width. Wide glazed openings need stiff steel designed to the door maker’s deflection limit
- Two storeys. More load, more steel, and often a party-wall question
- BCAR. Over 40 m², a Commencement Notice with compliance documentation, an inspection plan and statutory certificates, unless the owner opts out
- Planning drawings. Some engineers also prepare planning or tender drawings. Others work from an architect’s set
Bottom line
Budget €1,200–€3,500 for extension structural design in Ireland in 2026, plus BCAR certification if the extension is over 40 m². Check that inspections and the final certificate are in the quote. For a fixed fee for your extension, call 01 270 9764.
Want a fixed fee for your job? Call 01 270 9764.
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Frequently asked questions
Does the 45 m² exemption reduce engineering costs?
It removes the planning application, not the structural design. Foundations, steel and roof still need to comply with the Building Regulations, and you'll still want a certificate when you sell.
Is BCAR certification extra?
Usually, yes. Acting as designer and assigned certifier on an extension over 40 m² means preparing the inspection plan, carrying out more inspections and signing statutory certificates. It adds to the basic design fee. Quotes should show it separately.
How do I compare engineer quotes for an extension?
Check that each quote covers the same items: site visit, foundation and steel design, roof structure, drawings, steel schedule, inspections at foundation and steel stage, and the final certificate. The cheapest quote often leaves out the inspections.
Sources
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