Loft Conversion Cost in Northern Ireland: 2026 Price Guide

With moving house being expensive and disruptive, a loft conversion is often the most cost-effective way to add a bedroom without extending a property's footprint - a popular choice across Northern Ireland, including in Belfast, Derry/Londonderry, Lisburn and Newry.

Typical costs

• Rooflight (Velux) conversion: roughly £20,000-£35,000
• Dormer conversion: roughly £35,000-£50,000
• Mansard or hip-to-gable conversion: £50,000-£75,000+

Adding an en-suite, structural steels for an open-plan layout, or a staircase reconfiguration will all add to these figures.

What affects the price

Roof pitch and existing head height are the first things a builder will check - older Victorian and Edwardian terraces, found in many towns across Northern Ireland, often have steeper pitches than newer housing, which can mean less dormer is needed to hit a comfortable head height. Newer housing stock tends to have more standardised roof structures, which can make quoting more predictable.

Planning permission and party walls

Most loft conversions can be done under permitted development, provided the additional roof volume stays within set limits and materials match the existing house - though the planning system in Northern Ireland is administered separately from the rest of the UK, so always check the specific rules with your local council rather than assuming a guide written for England, Scotland or Wales applies. If your property is terraced or semi-detached, a Party Wall Agreement with your neighbours is usually required before work starts, which can add several weeks to the start date.