Two-storey extensions in Ireland
Reviewed October 2026 · Not legal, planning or financial advice
A two-storey extension adds a bedroom above new ground-floor space in one project, sharing foundations, roof and builder mobilisation.
Planning
The upper-floor allowance for exempted development is small — 12m² for terraced and semi-detached houses, 20m² for detached — and upper floors must be at least 2m from boundaries. Most full-width two-storey extensions exceed this and need planning permission. Overlooking and loss of light to neighbours are the usual planning concerns.
Cost
Per square metre, two-storey extensions are usually cheaper than single-storey ones because the same foundations and roof serve twice the floor area. In total they cost more and take longer, and staying in the house during works is harder.
Value
An extra bedroom is often the single change with the most effect on value, depending on the local market and on whether the result is proportionate to the house. Ask a local valuer before assuming.
Regulations and their interpretation change. This guide explains the position as we understand it in October 2026. Confirm what applies to your house with an architect, planning consultant or your local authority before relying on it.