Do I need planning permission for an extension in Ireland?

What exempted development means

The Planning and Development Regulations list classes of development that do not need planning permission. House extensions fall under Class 1 of Schedule 2, Part 1. The exemption covers extensions to the rear of a house (including conservatories) and the conversion of an attached garage, store or shed to the rear or side into part of the house.

Exempted development still has to comply with the Building Regulations. “No planning permission needed” never means “no rules”.

The main conditions for a rear extension

• Total floor area of the extension, together with any previous extensions built since 1 October 1964, must not exceed 40m².
• Above ground floor: no more than 12m² for a terraced or semi-detached house, 20m² for a detached house.
• Any part above ground floor must be at least 2 metres from any boundary.
• At least 25m² of private open space must remain, exclusive of the extension, to the rear or side of the house.
• Windows must be set back from the boundaries they face (separation distances differ for ground-floor and upper-floor windows).
• Wall and roof heights are limited relative to the existing house.
• The roof of the extension must not be used as a balcony or roof garden.

When the exemption does not apply at all

• The house is a protected structure and the works would materially affect its character.
• The house is in an Architectural Conservation Area and the works would affect the character of the area (check your development plan).
• A condition on an earlier planning permission removes exempted-development rights.
• The extension is to the side or front rather than the rear.
• The works contravene other restrictions set out in Article 9 of the Regulations.

What if my house has already been extended?

Earlier extensions count. If a previous owner added a 20m² kitchen in the 1990s, roughly 20m² of the 40m² allowance is gone. If an earlier extension was itself given planning permission, check that permission’s conditions — some remove further exempted-development rights. Your council’s online planning search shows the property’s planning history.

How much garden must I keep?

At least 25m² of private open space must remain to the rear or side of the house, not counting the extension. On a small terraced plot this, not the 40m² limit, is often the binding constraint. Measure the garden before deciding on depth.

Can I build to the boundary?

A single-storey rear extension can, subject to the other conditions, be built close to or on a boundary. Upper floors must be at least 2m from a boundary to be exempt. Building on a party wall raises separate issues of neighbour consent and structure that have nothing to do with planning — get advice early.

If you are unsure: a Section 5 declaration

You can ask your local authority for a declaration on whether proposed works are exempted development (a Section 5 declaration). A fee applies. It gives certainty that is useful when selling the house later.

If you need permission

A planning application needs drawings, a site notice and a newspaper notice. The council normally decides within eight weeks, after which there is a period during which a decision can be appealed to An Coimisiún Pleanála (formerly An Bord Pleanála). Allow roughly three to four months from lodging to being able to start, longer if further information is requested or an appeal is made.

What has changed recently?

The Government has consulted on changes to several exempted-development classes in recent years. We have not assumed any change we could not confirm as in force. Before relying on the limits above, check the current regulations on the Irish Statute Book or gov.ie, or ask your architect.