House Extension Cost in Belfast: 2026 Price Guide
08 Aug 2026
- Side return infill: £16,000-£26,500
- Single-storey rear extension: £22,500-£48,000
- Double-storey extension: £48,000-£87,000 upwards
A genuinely separate planning system
Planning in Northern Ireland is set under the Planning Act (Northern Ireland) 2011, entirely distinct from England, Scotland and Wales - permitted development-style thresholds exist but with their own specific rules, so always confirm directly with Belfast City Council rather than assuming a British extension guide applies.
Malone and Stranmillis versus the terraced inner city
The larger properties around Malone and Stranmillis, close to Queen's University Belfast, tend to have more room to extend into than the dense Victorian terraces of the Holyland or Sandy Row, where access and party wall considerations dominate the cost conversation instead.
What pushes costs up
As in any terraced city, narrow streets without side access mean materials go through the property - worth asking a builder directly whether this is priced into a quote.
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Frequently asked questions
How much does a house extension cost in Belfast?
A side return infill runs £16,000-£26,500, a single-storey rear extension £22,500-£48,000, and a double-storey extension £48,000-£87,000 upwards.
Do Malone and Stranmillis have more room for extensions than the Holyland?
Yes - the larger properties there, close to Queen's University Belfast, tend to have more room to extend into than the dense Victorian terraces of the Holyland or Sandy Row.
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