“How much will my extension cost?” is the first question almost every homeowner asks. The honest answer is that it depends – but it depends on a fairly predictable set of factors. Understanding them early helps you set a realistic budget and make design choices that give you the most space and value for your money.
Size and shape
Floor area is the biggest single driver, but shape matters too. A simple rectangular footprint with a straightforward roof is far more economical than a design with multiple corners, steps and roof valleys. Every extra corner adds foundations, brickwork, flashings and labour.
Single or two storey
A two-storey extension costs more overall, but the cost per square metre is often lower, because the same foundations and roof serve twice the floor space. If you may need more bedrooms in future, building up now can be better value than extending twice.
Ground conditions and foundations
What lies underneath your garden can have a real effect on price. Soft ground, nearby trees, drains running through the footprint or a sloping site can all mean deeper or specialist foundations. A site visit before pricing avoids surprises later.
Structural work to the existing house
Opening up the back of the house to create an open-plan space usually means steel beams, temporary support and building control inspections. Large openings and minimal-frame glazing look stunning but need more structural input.
Specification and finishes
Two extensions of identical size can differ widely in cost depending on what goes inside. Kitchens, bathrooms, glazing, roof lights, flooring and underfloor heating are where budgets most often grow. Decide early which items are essential and which can wait.
Fees and approvals
Allow for architectural drawings, structural engineer calculations, Building Control fees and, where needed, planning permission. Our guide to planning permission and Building Control in Northern Ireland explains what to expect.
Access and disruption
Tight access, terraced properties where materials must come through the house, or the need to keep a family living on site all affect how efficiently the work can be carried out.
How to keep costs under control
- Keep the footprint and roof simple.
- Fix your design and specification before work starts – changes mid-build cost the most.
- Get a detailed, itemised quotation rather than a single figure.
- Keep a contingency of around 10-15% for the unexpected.
Get an accurate price
SC Developments has been building extensions across Northern Ireland since 1995. We will visit your home, talk through what you want to achieve and give you a clear, detailed quotation. See our home extensions page or contact us to arrange a visit.
