If you’re planning to add space to your home, one of the first questions you’ll ask is about house extensions Cardiff pricing. Costs vary quite a bit depending on size, materials and the type of extension you choose. This guide breaks down realistic 2026 price ranges, the main factors that affect cost, and how to budget properly before you get started.
Average House Extension Costs in Cardiff for 2026
While every project is different, most homeowners can expect the following rough price ranges per square metre. These figures include materials and labour, but not fittings like a new kitchen or bathroom suite.
- Single-storey extension: £1,800 to £2,600 per square metre
- Double-storey extension: £1,600 to £2,300 per square metre
- Kitchen extension Cardiff projects: £2,000 to £3,000 per square metre
- Dormer loft extension: £35,000 to £55,000 total, depending on size
These figures are a starting point. A home extension Cardiff company can give you a far more accurate number once they’ve seen your property and understood exactly what you want.
What Affects the Cost of Your Extension?
Several factors influence the final price of any extension project. Understanding them helps you plan a realistic budget from the start.
1. Size and Layout
Larger extensions naturally cost more, but layout matters too. Simple rectangular designs are usually cheaper to build than complex shapes with multiple angles.
2. Type of Extension
A single-storey rear extension tends to cost less per square metre than a double-storey build or a loft dormer, mainly due to differences in structural work and foundations.
3. Materials and Finish
Standard brick and block construction is more budget-friendly than options like full-glass structures or bespoke timber frames. Your choice of flooring, windows and doors also affects the total.
4. Groundworks and Site Conditions
Sloping gardens, poor soil or difficult access can increase groundworks costs. A site visit early in the process helps avoid surprises later.
5. Planning Permission and Building Regulations
Some extensions fall under permitted development rules, while others need full planning permission. Application fees and any required drawings add to your overall budget.
6. Kitchen and Bathroom Fit-Outs
If your extension includes a kitchen extension Cardifflayout with new units, worktops and appliances, this is usually priced separately from the build itself and can range widely based on your choices.
How to Budget for Your Extension
Here’s a simple step-by-step approach to planning your budget realistically:
- Set a total budget, including a 10 to 15 percent contingency fund
- Get quotes from at least two or three experienced local builders
- Ask for an itemised breakdown, not just a single lump sum figure
- Factor in fittings, decorating and furniture separately from the build cost
- Confirm payment stages tied to project milestones, not upfront in full
Building in a contingency fund is especially important, since older Cardiff properties can sometimes reveal unexpected issues once work begins.
Tips to Keep Your Extension Costs Under Control
A few practical choices can make a real difference to your final bill.
- Keep the footprint simple rather than adding unnecessary angles
- Reuse existing drainage and utility connections where possible
- Choose mid-range finishes instead of premium fittings throughout
- Plan the design fully before work starts to avoid costly changes mid-build
- Work with a builder who offers guidance on cost-effective alternatives
Why Work With Legion Developments Ltd
Legion Developments Ltd is a family-run team delivering house extensions Cardiff homeowners are proud of, from single-storey rear extensions to full dormer conversions. The team handles everything from initial design conversations through to groundworks, building and finishing touches.
Because Legion Developments Ltd works across South Wales on extensions, kitchens, driveways and new builds, you get one accountable team managing your project from start to finish. Getting a free quote is the easiest way to find out what your extension will realistically cost.
