What happens if you build without planning permission in Ireland?

Any development that needed planning permission but did not get it, or that was built other than in accordance with a permission that was granted, is classed as unauthorised development under the Planning and Development Act 2000 (as amended). This covers everything from a new house built without permission to an extension that ended up larger, taller, or positioned differently than what was approved. The fact that works have been completed, or completed some years ago, does not make them lawful; unauthorised status generally persists until the situation is regularised.

Local authorities have statutory powers to investigate complaints or their own observations of suspected unauthorised development. If a breach is confirmed, the planning authority can issue a warning letter followed by an enforcement notice requiring the works to be altered, removed, or an application for retention permission to be made. Non-compliance with an enforcement notice is an offence and can lead to prosecution, court-ordered remedial works, and in serious cases substantial fines or imprisonment, with the local authority able to recover its costs from the owner.

In practice, many unauthorised works are resolved through a retention permission application, which asks the planning authority to assess and, if appropriate, formally permit development that has already been carried out. Retention is not automatic and is assessed against normal planning criteria; if it is refused, the authority can require demolition or reinstatement. Because enforcement action and unresolved planning status can complicate conveyancing, mortgage approval, and future extensions, it is generally far cheaper and safer to regularise a breach voluntarily than to wait for enforcement.