Extension cost per m² in Belfast
Extension cost by size in Belfast
Each row multiplies the current £1,800–£3,000 per m² national benchmark by floor area and then applies the same regional factor.
What can change a real Belfast quote?
- Floor area and number of storeys
- London and regional labour rates
- Steelwork and structural changes
- Kitchen or bathroom installation
- Glazing and door specification
- Finish level, access and contingency
Local planning considerations
Northern Ireland has different policy and grant arrangements from Great Britain, so scheme-specific calculator assumptions should be checked carefully.
- Northern Ireland regulations, approvals and support schemes should be checked independently from England, Wales and Scotland guidance.
- Regional material supply, specialist-trade availability and travel can affect individual quotes beyond the broad model factor.
- For major refurbishment, keep surveys, remedial work and compliance costs separate from visible finish upgrades.
How the regional model works
The 0.89× factor places this planning estimate 11% below the national planning baseline. We keep that modelling assumption separate from the dated national benchmark so users can see which part comes from an external source and which part is UK Home Costs modelling.
Sources
House Extension: Cost Breakdown 2026
Published / checked: June 2026
Used for: Extension cost-per-m² benchmarks and common add-on costs
Construction output price indices
Published / checked: 13 August 2026
Used for: Construction price trend and update checks
Frequently asked questions
How much does a house extension cost in Belfast in 2026?
Our modelled Belfast planning rate is about £1,600–£2,650 / m², based on the current national £1,800–£3,000 per m² benchmark and the Northern Ireland regional factor. This is not an observed city-wide quote average.
How much is a 20m² extension in Belfast?
Applying the same regional model gives about £32,050–£53,400 before VAT for a straight-line 20m² example. Structural work, glazing, kitchens, bathrooms and access can move a real quote outside that range.
Why is the Belfast estimate different from the UK benchmark?
UK Home Costs applies a 0.89× Northern Ireland planning factor, placing the model 11% below the national planning baseline. It is our modelling assumption rather than an external city price index.
Does the extension figure include VAT and professional fees?
The national benchmark is stated before VAT. Do not assume architect, structural engineer, planning, building-control, party-wall or specialist survey fees are included unless a contractor quote says so.