Build a single-storey extension.

A single-storey brick extension is the most-built improvement in UK housing — kitchen extensions, side returns, rear extensions, and orangeries. The numbers add up fast and the project takes months. This guide covers what extension brickwork actually costs in 2026, the full process from design to keys, and the planning rules that apply.

Extension costs vary enormously by region — London + South East premium is 40–60% above national average.

What Does the Work Involve?

• Design and structural engineering.
• Planning permission application (4–8 weeks) — or check for permitted development.
• Building Control approval.
• Site preparation, excavation, foundations.
• Brick wall construction with cavity insulation, tied to existing structure.
• Roof construction and weatherproofing.
• Windows, doors, render or cladding finishing.
• Internal finishing (out of brickwork scope but part of total).

Typical Costs (per m²)

Brickwork is typically 25–35% of total extension cost. Roof, glazing, and internal fit-out make up the rest.

How Long Does It Take?

• Planning permission: 4–8 weeks (sometimes longer for objections).
• Building Regs: 2–6 weeks.
• Construction: 8–16 weeks depending on size and complexity.
• Total timeline: 5–10 months realistic.

DIY or Professional?

Specialist building contractors only. Extensions involve foundations, structural calculations, multiple trades, services connection, and Building Control compliance — far beyond DIY scope.

Choosing the Right Tradesperson

• Look for builders with similar-sized extensions in their portfolio.
• Confirm structural engineer involvement at design.
• Discuss project management — daily / weekly coordination.
• Get a JCT minor works contract or similar formal agreement.
• Confirm insurance and warranty cover (typically 10 years on structural works).

UK Regulations

• Extensions over 4 m beyond rear wall (detached) or 3 m (other) need planning permission.
• Two-storey rear extensions over 3 m need planning.
• Side extensions over half the original house width need planning.
• Building Regulations apply to all extensions — engineer-signed structural work required.
• Party Wall Act applies if working near boundaries.
• Listed and conservation properties have additional consent requirements.

Common Problems

• Foundation issues — poor soil, tree roots, existing foundations. Discovered during excavation; adds cost.
• Brick matching — matching existing brick is harder than expected. Reclaimed bricks often the answer.
• Timeline overruns — extension projects routinely overrun by 20–30%. Plan accordingly.
• Cost overruns — variation orders during construction. Budget 10–15% contingency.
• Damp/water ingress — junction between old and new construction is the vulnerable area.

Frequently Asked Questions