If you’re considering a house extension in Croydon, one of the first questions you’ll ask is: how much will it cost?
The answer depends on several factors — including the size of the extension, structural requirements, design complexity and specification level. In this guide, we break down realistic 2026 cost ranges, planning considerations and what influences your final budget.
If you are looking for tailored advice, you can also explore our dedicated House Extension Services in Croydon page.
Average House Extension Costs in Croydon (2026)
As a general guide:
- Single-storey rear extension: £1,800 – £2,800 per m²
- Two-storey extension: £2,000 – £3,000 per m²
- Side return extension: £1,900 – £2,700 per m²
For example:
- 20m² single-storey extension → £36,000 – £56,000
- 40m² two-storey extension → £80,000 – £120,000
These figures typically include structural works, roofing, insulation and basic finishes. High-end kitchens, glazing systems or structural steel complexity can increase costs.work later.
What Affects the Cost of a House Extension?
1. Size & Structure
The larger the extension, the greater the material and labour costs. Structural steel (RSJs), foundation depth and load-bearing changes significantly impact the budget.
2. Planning & Design Requirements
In Croydon, some extensions fall under permitted development, while others require full planning permission. Complex planning conditions may increase architectural and consultancy fees.
3. Specification Level
Finishes such as:
- Aluminium bifold doors
- Skylights or roof lanterns
- Underfloor heating
- Bespoke joinery
can increase the final project cost.
4. Ground Conditions
Poor soil, drainage adjustments or underpinning may require additional structural work.
Do You Need Planning Permission in Croydon?
Many rear extensions fall under permitted development, but this depends on:
- Property type (terraced, semi-detached, detached)
- Conservation area restrictions
- Extension depth and height
We recommend confirming planning requirements early to avoid delays. You can also read our detailed planning guidance in the Planning & Building Regulations section of our guides.
How Long Does a House Extension Take?
Typical timelines:
- Design & approvals: 6–10 weeks
- Construction phase (single-storey): 10–14 weeks
- Two-storey extension: 14–20 weeks
Weather conditions, material lead times and structural complexity can influence schedules.
Ways to Manage Your Extension Budget
- Finalise design before construction
- Avoid mid-build specification changes
- Work with experienced builders familiar with Croydon regulations
- Plan contingencies (typically 10%)
Is a House Extension Worth the Investment?
In Croydon and South London, well-designed extensions can:
- Increase property value
- Improve layout functionality
- Avoid the cost of moving
- Add long-term lifestyle benefits
When properly designed and structurally integrated, an extension can offer strong return on investment.
Considering a House Extension in Croydon?
If you’re planning a single-storey, side return or two-storey extension, our team provides full project management — from structural design to final finishes.
Visit our House Extensions Croydon page to learn more or request a consultation.
