Quick start:

What are you building?

Internal floor area: 30 m² (323 sq ft)

Storeys

Finish level

Where in the UK?

Ground type

Site access for diggers & deliveries

Kitchen & bathrooms

New kitchenBathrooms

Site checks

Trees within ~10 m of the build Old fuse box / no spare capacity

Contingency: 10%

Optimistic

£78,948

Everything goes right, no surprises

Realistic

£91,590

Includes 10% contingency

Worst case

£101,265

+15% for hidden problems & delays

Per m² (realistic)

£3,053

Materials

£28,650

Labour

£35,850

Start to keys

26 wks (~6.0 mo)

What's in the price

Build shell & structure£55,500
Kitchen (standard)£9,000
Professional fees (architect, engineer, Building Control, Party Wall)£7,740
VAT at 20%£12,900

Build order & timeline

1. Design & approvals

14w

2. Site prep & groundworks

3. Superstructure & shell

4. First fix

5. Plaster & second fix

6. Fit-out, finishes & handover

Week 0Week 26

Stage 1: Design & approvals

wk 0–14 · £7,740

Measured survey & architect drawings
Planning permission or permitted-development check (8 wks)
Party Wall notices if near a boundary
Structural engineer calcs
Building Control application
Tender to 3+ builders

Before moving on: Planning decision + Building Regs plans approved

Stage 2: Site prep & groundworks

wk 14–16 · £9,675

Site set-up, welfare, skips
Strip & excavate foundations
Drainage diversion / new runs
Pour foundations
Blockwork to DPC, oversite slab

Before moving on: Building Control: foundation & drainage inspection

Stage 3: Superstructure & shell

wk 16–20 · £22,575

Walls & cavity insulation
Steels / lintels
Floor joists (multi-storey)
Roof structure & covering
Windows & external doors — watertight

Before moving on: Watertight + Building Control structural check

Stage 4: First fix

wk 20–22 · £9,675

Electrics first fix (cables, back boxes)
Plumbing & heating pipework
Ventilation ducting
Stud walls & insulation

Before moving on: Pre-plaster inspection — photograph everything

Stage 5: Plaster & second fix

wk 21–23 · £9,675

Plasterboard & skim (dry 1–2 wks)
Screed floors
Sockets, switches, lights
Radiators / UFH manifold
Doors, skirting, architrave

Before moving on: Electrical cert (Part P) + gas safe cert

Stage 6: Fit-out, finishes & handover

wk 23–26 · £12,900

Kitchen & bathrooms
Flooring & tiling
Decoration
External works & landscaping
Snagging walk-round

Before moving on: Building Control completion certificate

Don't get caught out

Never pay more than 10–15% up front. Pay in stages, only after each checkpoint above is signed off.
Get 3 like-for-like quotes from the same drawings — a quote far below this range usually means "provisional sums" that grow later.
Retain 2.5–5% for 6 months after completion to cover snagging.
Ask for public liability insurance, a written contract (e.g. JCT Homeowner) and a schedule of works.

Indicative 2026 UK figures — always get written quotes.