A dependable Building Cost Estimator UK turns your drawings into a measured cost plan: you input scope and area, it applies RICS NRM rules, benchmarks and live quotes, then adds prelims, overhead and profit, fees, inflation and contingency so you can budget with confidence.

If you’re budgeting for a UK extension, loft or new build, this page shows how to use a building cost estimator properly, with typical £/m² ranges and the steps professionals follow. For a deeper framework see Construction Cost Estimating – A Comprehensive Guide, our explainer on RICS New Rules of Measurement, and price context in How Much Does It Cost to Build a House? Looking for a Building Cost Estimator UK you can use online? Try our online route too.

Executive Answer

Headline homeowner budgets (inc VAT): single-storey extensions £1,900–£3,200 per m²; double-storey £1,650–£3,000 per m²; loft conversions £1,250–£2,200 per m²; new builds £1,800–£3,200 per m². Add prelims 7–12%, overhead & profit 10–15% on net trades, professional fees 10–15%, inflation for the start date, and contingency 10–15% at early design.

Region: England (GB)   VAT: homeowner figures shown including VAT unless noted   Units: m², m, l/m, m³   Currency: GBP

• Cost Summary
• Assumptions and Methodology
• How to Use a Building Cost Estimator UK
• Detailed Cost Breakdown
• Programme and Durations
• Regional Variation
• Inclusions and Exclusions
• Risks and Allowances
• FAQs
• Sources
• Key Facts & Assumptions (At a Glance)

Next step: Request a Custom Estimate for your drawings and scope. Or check Pricing for turnaround options.

Cost Summary

Base date Q4 2025. Typical homeowner budgets inc VAT for England, assuming standard access, mid-range specification and no abnormals.

Scenario	Unit	Low £	High £	Typical £	What moves the number
Single-storey extension	m²	1,900	3,200	2,400	Structure, access, kitchen/bath fit-out level
Double-storey extension	m²	1,650	3,000	2,300	Economies from shared prelims and roof
Loft conversion (dormer)	m²	1,250	2,200	1,700	Structure, stairs, dormer size, insulation
New build house	m²	1,800	3,200	2,400	Form of construction, glazing %, services
Professional fees	% of build	10%	15%	12%	Architect, structural engineer, approvals
Contingency (early design)	% of build	10%	15%	12.5%	Reduce to 5–10% when tendered
Preliminaries	% of net	7%	12%	10%	Site setup, welfare, scaffolds, supervision
Overhead & Profit	% of net	10%	15%	12%	Builder margin on trades

Assumptions and Methodology

Measurement: quantities and definitions aligned to RICS NRM. Design stages: methods matched to the RIBA Plan of Work (order-of-cost at Stage 1, elemental at Stages 2–3, analytical at Stage 4).

Build-up we apply

1. Measure direct works by element or work section
2. Price trades with benchmarks, then replace with live quotes
3. Add preliminaries tied to programme
4. Apply overhead and profit on net trades
5. Include professional and statutory fees
6. Set inflation to the start date using current indices
7. Carry contingency by design stage and known risks

How to Use a Building Cost Estimator UK

1) Fix scope and upload complete information

Provide drawings, structural notes, a short spec/finishes list, and site photos. Clear inputs mean better outputs.

2) Choose the right estimating method for your stage

At early stage, a calibrated £/m² is fine. As you approach tender, switch to measured quantities and supplier quotations.

3) Check the basis statements

Look for base date, VAT stance, region, prelims, margin, risk and inflation called out explicitly.

4) Stress test the result

Run best/worst cases on key materials, productivity and programme; move the start date to test inflation exposure.

5) Keep a change log

Track what moved between revisions and why. It speeds up approvals and avoids disputes.

Detailed Cost Breakdown

Typical allowances and unit rates for small residential projects in England, inc VAT unless noted. Always verify with live quotes.

Scope	Unit	Low £	High £	Typical £	Notes
Strip foundations (600 mm)	m	85	140	110	Excludes pump; typical soil
Trench fill concrete (GEN1–C20)	m³	130	180	155	Supply and place
External brickwork	m²	120	180	150	Facing brick, ties, mortar
Internal blockwork 100 mm	m²	55	95	75	Lightweight blocks
Roof tiling (concrete)	m²	75	130	105	Incl membrane, battens, ridge
Windows uPVC, supply & fit	m²	450	750	600	FENSA installer
Plasterboard & skim	m²	18	30	24	Two-coat skim
Electrical first & second fix	per point	75	120	95	Includes testing; Part P
Plumbing first & second fix	per point	100	180	140	Incl pipework and connections
Kitchen allowance (mid)	each	15,000	25,000	20,000	Units, worktops, appliances, fit
Bathroom allowance (mid)	each	4,000	10,000	7,000	Suite, tiling, shower screen

Programme and Durations

• Pre-construction: surveys 1–2 weeks; planning decision 8–12 weeks typical; building control plan check 2–4 weeks
• Lead times: windows 4–10 weeks; kitchens 6–10 weeks; steel 2–5 weeks; MEP kit 4–8 weeks
• On site: single-storey extension 10–16 weeks; double-storey 14–22 weeks; loft 6–10 weeks
• Tender period: 2–4 weeks for small residential; allow 1–2 weeks for clarifications

Regional Variation

Location affects labour, logistics and prelim time. A simple guide: London and inner M25 often 10–20% above GB average; South East 5–10% above; parts of the North and Midlands 5–15% below. Always calibrate with local quotes and current indices.

Inclusions and Exclusions

Included in the figures above

• Normal access and working hours
• Standard foundations for typical ground
• Mid-range finishes unless noted
• Prelims, overhead and profit shown separately

Common exclusions

• Abnormals: poor ground, party wall works, major utility upgrades
• Complex planning conditions or heritage requirements
• Client-supplied items outside allowances

New to comparing quotes? Read The Ultimate Guide to Obtaining a Building Estimate and our Residential Construction Estimates.

Risks and Allowances

• Contingency: 10–15% at early design; 5–10% at tender
• Inflation: apply a start-date allowance using current indices and tender price trends
• Regulatory: planning and building control fees, plus CDM dutyholder duties on multi-contractor projects
• VAT: most domestic alterations at 20%; some new dwellings can be zero-rated when conditions are met

Keep an eye on market updates and indices when setting fixed-price periods.

Worked Example: Small Kitchen Extension

Inputs

• 12 m² single-storey rear extension, mid-range kitchen, standard access
• Assume simple foundations, standard glazing, no abnormals

Estimator steps

1. Apply £/m² typical £2,400 inc VAT → build subtotal ≈ £28,800
2. Add kitchen allowance £20,000 (mid-range) → £48,800
3. Add prelims 10% of net trades → +£4,880
4. Add O&P 12% of net trades → +£5,856
5. Fees 12% of build (ex allowances) → guide +£3,500–£5,500
6. Contingency 10–15% at this stage → +£5,000–£7,500

Result: early budget range £68k–£73k inc VAT, subject to quotes, access and specification.

FAQs

Is a Building Cost Estimator UK accurate?

For early budgeting it’s a strong guide. Accuracy improves as allowances are replaced with supplier quotes and measured quantities.

What drawings do I need?

Plans and elevations, any structural notes, and a basic specification or finishes list. Site photos and access notes help.

How do preliminaries and margin work?

Prelims cover site setup, welfare, scaffolds and supervision. Overhead and profit is the builder’s margin, typically applied to net trade costs.

Do I include VAT?

Yes for homeowner budgets. New dwellings can be zero-rated when conditions are met under HMRC rules.

What about planning and building control fees?

Allow for the latest application fees and plan-check/inspection charges; they vary by authority and submission type.

Sources

• RICS New Rules of Measurement (NRM)
• RIBA Plan of Work
• ONS Construction Output Price Indices
• BCIS construction industry forecast
• Planning application fees in England (from 1 April 2025)
• HMRC VAT Notice 708: Buildings and construction

Key Facts & Assumptions (At a Glance)

• Primary keyword: Building Cost Estimator UK
• Audience: Homeowner budgets for small to medium residential
• Region: England (GB)
• VAT stance: figures shown inc VAT unless noted
• Units: m², m, l/m, m³, per point
• Measurement: RICS NRM; methods aligned to RIBA stages
• Contingency: 10–15% early; 5–10% later

Cost disclaimer: Figures are guidance only based on typical access, specification and market conditions at the base date. Always verify with measured quotes for your site, design and start date.

Next step: Request a Custom Estimate. Compare approaches with our online estimators guide and learn the fundamentals in our estimating pillar.