Home Extensions in Dun Laoghaire, Dublin

A standard single-storey rear extension costs €2,000 to €3,500 per square metre in Ireland. A 20 sq m kitchen extension therefore costs €40,000 to €70,000. A 40 sq m open-plan extension runs €80,000 to €140,000. Two-storey extensions cost €1,800 to €3,000 per square metre because foundation and roof costs are shared. These figures include the build but not architect's fees (8-12% of build cost), planning permission (€65 application fee), or kitchen/bathroom fit-out. Dublin prices are 15-25% above the national average.

Many single-storey rear extensions up to 40 sq m are exempt from planning permission under exempted development rules. However, exemptions come with strict conditions: the extension cannot exceed certain height limits, must not reduce the rear garden below 25 sq m, and the total floor area of all extensions cannot exceed the original house's floor area by more than a set amount. Two-storey extensions generally require planning permission. If your home is a protected structure or in an Architectural Conservation Area, different rules apply. Always verify with your architect or local authority before assuming exemption.

A straightforward single-storey rear extension typically takes 10 to 16 weeks from breaking ground to handover. A two-storey extension takes 14 to 22 weeks. If planning permission is required, add 8 to 12 weeks for the application process. Design and tendering take another 4 to 8 weeks before work starts. In total, expect 6 to 9 months from first meeting your architect to moving into the finished extension. Weather delays (particularly in winter), material supply issues, and subcontractor scheduling can all extend the timeline.

Legally, you do not need an architect for small exempt extensions, but it is strongly advisable for anything beyond a very basic box. An architect ensures your extension is well-designed (maximising light, space, and flow), compliant with building regulations, and properly documented for building control. They also manage the tender process, inspect the work during construction, and handle snagging. Architect's fees are typically 8 to 12% of the build cost, and for most homeowners the investment pays for itself in a better result and fewer problems.

Open-plan kitchen-living-dining extensions add the most value because they create the type of living space that Irish buyers now expect. Large glazed openings onto the garden (sliding or bi-fold doors) are highly desirable. Underfloor heating in the new space is a relatively low-cost add that buyers value. A well-designed utility room and good storage are also consistently cited by estate agents as value-adding features. Poorly designed extensions that create awkward layouts or block light from existing rooms can actually reduce value.

Under Irish building regulations, you must submit a Commencement Notice to the Building Control Authority via the BCMS online system at least 14 days before work starts. For extensions over 40 sq m, this is a Statutory Commencement Notice, which requires an assigned certifier (architect or engineer) and supporting documentation. For smaller extensions, an optional Commencement Notice may be used. Your architect or engineer handles this paperwork. Non-compliance with building control can create serious problems when you come to sell.