Home Extension Costs Explained: Budget Guide for 2026

Planning Your Budget

One of the most common questions we get is "How much will my extension cost?" The answer, of course, is "it depends," but in this guide, we'll break down the averages to give you a solid starting point.

Average Cost Per Square Metre

As of 2026, basic construction costs in the UK typically range from:

• Single Storey Extension: £1,800 - £2,800 per m²
• Double Storey Extension: £1,500 - £2,300 per m² (often cheaper per m² due to shared foundations/roof)
• High-Spec Finishes: £3,200+ per m²

The "Hidden" Costs

The build cost is only part of the picture. Don't forget to budget for:

• Architect Fees: 3-7% of construction cost.
• Structural Engineer: £500 - £1,500.
• Planning Application: ~£206.
• Building Regulations Checks: £500 - £1,000.
• VAT: 20% on top of almost everything (unless you are in a specific reduced rate category).

Factors That Inflate Cost

Site Access: If materials have to be hand-balled through a terraced house, labour costs skyrocket.

Soil Conditions: Poor soil might require piled foundations, costing thousands more.

Glazing: Large bi-fold doors or roof lanterns are premium items.