Know what your build should cost in Northern Ireland
Most cost calculators quote UK averages. Northern Ireland runs roughly 15 to 20 per cent below that, so a national tool will overstate your budget by thousands. Every calculator here is priced from your postcode, and shows exactly where the money goes.
Start with the calculator that matches your project
Each one asks a handful of questions, then gives you a range, a full breakdown and the assumptions behind it. No email required, no sign-up.
Extension
Free house extension cost calculator for Belfast and Northern Ireland. Instant estimate with a full cost breakdown, fees and contingency. Updated for 2026.
Loft conversion
Free loft conversion cost calculator for Belfast and Northern Ireland. Rooflight, dormer, hip-to-gable and mansard prices with fees and contingency.
Loft Insulation
Free loft insulation calculator for Belfast and Northern Ireland. Rolls to order, installed cost, U-value before and after, and a realistic annual saving.
Wall insulation
Free wall insulation calculator for Belfast and Northern Ireland. Compare cavity, external and internal insulation costs, U-values and realistic savings.
Bricks
Work out how many bricks you need for any wall, plus packs, sand and cement, with 2026 Northern Ireland brick and bricklaying prices and full workings.
Concrete
Work out how much concrete you need for a slab, footing or post holes, with cement, sand and aggregate quantities and 2026 Northern Ireland prices.
Driveway
Free driveway cost calculator for Belfast and Northern Ireland. Block paving, tarmac, resin, gravel and concrete prices per square metre for 2026.
Roof
What a new roof costs in Belfast and Northern Ireland in 2026: concrete tile, clay, fibre-cement and natural slate, with scaffolding and stripping included.
A UK average is the wrong number for a Belfast job
Labour is the biggest variable in any building project, and it does not cost the same across the UK. A tradesperson in Northern Ireland charges a fraction of a London day rate, and materials delivered to a Belfast site do not carry the same haulage premium.
Every calculator here starts from a UK-average base rate and then applies the multiplier for your postcode. Type BT9 and you get Belfast prices. Type SW1 and you get London prices. The difference is not small.
Same 25m² extension, four postcodes
Indicative all-in cost for a standard specification rear extension.
Illustrative only, using the same regional multipliers the calculators apply.
Browse by the kind of work you are planning
Extensions
Single storey, double storey, rear, side and wrap-around
Loft & Conversions
Lofts, garages, garden rooms and outbuildings
Insulation & Energy
Loft, wall, floor and roof insulation with U-value modelling
U-valuesMaterials
Bricks, blocks, concrete, mortar, fencing and paving quantities
Driveways & Outside
Driveways, patios, decking and garden walls
Renovation
Kitchens, bathrooms, roofs, windows and rewires
Three steps, about ninety seconds
1. Answer a few questions
Size, specification, postcode and anything extra. Nothing technical, and nothing you need a drawing for.
2. Get a costed range
A low and a high figure, with every line broken out: construction, extras, professional fees and contingency.
3. Compare against real quotes
Take the estimate to your builder, or let us match you with three local ones. Either way you now know what fair looks like.
Guides for Northern Ireland homeowners
Planning rules, building control, and what things actually cost here.
Roof Replacement Costs in Northern Ireland: 2026 Price Guide
What a new roof costs in Northern Ireland in 2026 — concrete tile, clay, fibre-cement and natural slate per m², plus scaffolding and what the strip reveals.
How to Choose a Builder in Belfast - 12 Questions to Ask
Twelve questions to ask a Belfast builder before you sign anything, what a good answer sounds like, and the consumer protections that apply in NI.
Block Paving vs Tarmac Driveways in Northern Ireland
Block paving costs £70 to £105 per m² in NI, tarmac £55 to £85. Here is the honest comparison on price, lifespan, repairs, drainage and our weather.
Next step
Get three free quotes from Northern Ireland builders
An estimate tells you whether a quote is fair. Tell us about your project and we will put it in front of builders working in your area. No cost, no obligation.