Do I need planning permission for an extension?

Extensions up to 40 sqm to the rear of a house are generally exempt from planning permission (subject to conditions). Side extensions, front extensions, and anything over 40 sqm need full planning permission. Always check with your local authority.

How long does a house extension take?

A single-storey rear extension typically takes 12-16 weeks from breaking ground to completion. Two-storey: 16-24 weeks. Add 4-8 weeks for planning permission if required, and 4-6 weeks for detailed design and tendering.

Should I get a fixed price or cost-plus quote?

Fixed price gives certainty but builders add a contingency margin. Cost-plus (actual costs plus a management fee) can be cheaper but you carry the risk of overruns. For extensions, fixed price with a clear scope and allowances for client selections is usually best.

Are you a builder? Quote extensions professionally

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House Extension Cost Ireland 2026: Cost Per Sqm Guide

House Extension Cost Ireland 2026: Single-storey rear extension €2,200 to €3,200/sqm. Two-storey extension €1,800 to €2,800/sqm. Side return €2,500 to €3,500/sqm. Sunroom €1,500 to €2,500/sqm. A typical 20 sqm kitchen extension costs €44,000 to €64,000. Extensions up to 40 sqm to the rear generally exempt from planning permission. Cost breakdown: groundworks 8-12%, structural 15-20%, roof 10-15%, windows 8-12%, first fix 10-15%, second fix 10-15%, finishing 8-12%, professional fees 5-10%.

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