Single Storey Extension Cost UK

Single Storey Extension Cost by Size

Costs assume brick & block construction, builder-grade finishes, and basic kitchen/bathroom fit-out. Excludes architect fees, planning, and structural engineer.

What's Included in the Build Cost

A typical single storey extension build quote includes:

• Strip foundations and concrete fill
• External brick and block walls
• Roof structure and covering (flat or pitched)
• Doors and full-height sliding or bi-fold doors
• Windows (double or triple glazed)
• Insulation to current Building Regulations (SAP 10)
• First-fix electrics, plumbing and heating
• Plastering, drywall and decoration
• Damp proof course and waterproofing
• Waste pipe runs and connections

What Costs Extra

• Kitchen or bathroom fit-out (units, worktops, appliances, sanitaryware) — £5,000–£30,000+
• Underfloor heating — £1,500–£4,000
• Skimming or re-plastering of existing walls adjacent to extension — £500–£2,000
• New boiler or heating upgrades if extension significantly increases heating load — £2,000–£6,000
• Structural steel to open up between existing house and extension — £1,500–£5,000
• Landscaping to step outside — £2,000–£8,000

Does a Single Storey Extension Add Value?

Almost always yes — if done well and appropriate for the property and area. A £50,000 extension that adds £75,000+ to a property's value is a typical outcome in most of the UK.

The key is matching the quality and scale to the property. A mid-spec extension on a mid-value property works well. Over-improving with premium finishes in a modest property rarely makes financial sense.