Many online calculators promise quick answers, but the reality is that the true cost of a project only becomes clear once detailed drawings and specifications are prepared.
Typically, the most accurate pricing comes after:
- Architectural drawings are completed
- A full Scope of Works is produced
- Structural engineering details are prepared
- Contractors submit 3–4 competitive tender quotes
When advising homeowners, we often start by looking at construction cost per square metre, which provides a helpful early budgeting guide. Our aim is to help homeowners understand likely costs early in the process and avoid unexpected surprises later.
Based on our experience with residential projects in London, typical construction costs fall within the following ranges:
- Single-storey Extension: £3,000 – £3,500 per m²
- Additional Storey: £1,200 – £1,600 per m²
- Loft Conversion: £1,500 – £2,500 per m²
- New Basement: £2,500 – £4,500 per m²
- Internal Refurbishment: £500 – £1,400 per m²
In addition to the above, homeowners should also plan for the following:
- Chimney Removal: £2,000 – £5,000 per chimney
- Bathroom: £5,000 (basic specifications) – £15,000+ (premium specifications)
- Kitchen (6m length): £6,000 (basic specifications) – £40,000+ (premium specifications)
However, these figures should be treated as ballpark estimates only, as material costs and labour prices can fluctuate. If you’re considering a house extension or refurbishment, the best approach is to plan your budget early and work with experienced professionals who’ll help to ensure your aspirations align with your budget, planning constraints, and long-term goals for the property.
Please also refer to this article for Other Costs to Consider in a Construction Project, and this article for the Cost to Hire an Architect.
Every home is different, and the most successful projects come from careful planning, clear cost advice, and experienced design guidance. If you are considering a house extension or refurbishment in London, working with an experienced architectural practice can help you maximise your space while keeping the project financially achievable.
Book a free consultation to see how we can help you optimise your requirements and deliver a project that meets both your vision and your budget.
