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Can I build a two-storey extension without planning permission in Ireland?

Sometimes, but the conditions are much stricter than for a single-storey extension. Class 1 of Schedule 2 to the Planning and Development Regulations 2001 allows a two-storey rear extension as exempted development only within tighter floor area, height and boundary-distance limits.

A two-storey extension can qualify as exempted development in Ireland, but the Planning and Development Regulations 2001 impose noticeably tighter conditions than for a single-storey extension. Under Class 1 of Schedule 2, the overall 40 m² cumulative floor area limit still applies, but a two-storey extension must also satisfy additional requirements relating to its position relative to the side and rear boundaries, and it must not reduce the distance between any window of a habitable room and the boundary below the minimum set out in the class.

In particular, a two-storey extension is generally required to be set back from the side boundary, and where it comes with a proposed rear extension it must not, taken together with any previous extensions, breach the overall floor area and open-space conditions. Some local authorities and the regulations themselves also restrict two-storey extensions on terraced or narrow-fronted houses because of overshadowing and overlooking concerns for neighbouring properties.

Because two-storey extensions have a much greater impact on neighbouring amenity — through overshadowing, loss of light, and overlooking — they attract closer scrutiny, and a relatively small breach of a height, setback or floor-area condition removes the exemption entirely. In practice, many two-storey extensions in more constrained sites end up needing full planning permission even where a similar single-storey extension would be exempt.

Conditions specific to two-storey extensions

Check each of these before assuming a two-storey extension is exempt:

  • The combined floor area with any previous extensions is within the 40 m² cumulative limit
  • The extension is set back an adequate distance from the side boundary
  • Upper-floor windows do not breach minimum distances to the boundary or to neighbouring habitable-room windows
  • The roof design and overall height comply with the limits in Class 1
  • The remaining private open space to the rear of the house is at least 25 m²
  • The house is not terraced or semi-detached in a configuration that the regulations exclude
  • The property is not a protected structure or in an architectural conservation area

Given how easily these conditions can be breached, it is common practice to get professional advice, and often a section 5 declaration, before committing to a two-storey design.

When permission is the safer route

If the site is narrow, close to a boundary, or the extension would overlook a neighbouring garden or window, it is usually more reliable to apply for planning permission directly. A full application allows the design to be assessed on its planning merits and gives statutory certainty, whereas relying on an exemption that turns out to be invalid can result in an enforcement notice or difficulty selling the property later.

Sources

Last reviewed 20 August 2026. General information only — not legal or planning advice.

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