1 Project location
Regional construction indices based on UK tender returns.
2 Project type
Select the closest matching work category.
🏡
Rear extension
single storey
From £900/m²
🏠
Rear extension
double storey
From £1,350/m²
🏘️
Wrap-around extension
From £1,600/m²
🏚️
Loft conversion
From £1,700/m²
🚗
Garage conversion
From £1,100/m²
🏡✨
New build
From £2,100/m²
4
Pre-construction surveys & investigations
These items identify constraints, risks and compliance issues early.
Measured & structural investigations
Measured building survey
Accurate existing drawings for design & planning.
+2%
Topographical land survey
Levels, boundaries, drainage, trees and site data.
+3%
Trial pits / soil investigations
Foundation conditions, soil type & bearing capacity.
+4%
Utilities, drainage & constraints
CCTV drainage survey
Identifies defects and required diversions.
+2%
Underground utilities search
Locates gas, electric, water & telecoms routes.
+1.5%
Asbestos survey
Required before demolition in pre-2000 buildings.
+2%
Environmental & regulatory reports
Ecology assessment
Checks for bats, nesting birds + protected species.
+2%
Arboricultural report
Tree constraints, RPAs, protection guidelines.
+3%
SAP / energy modelling
Required for energy compliance and glazing strategy.
+1.5%
Specialist consultants
Heritage consultant
Listed buildings, conservation guidance.
+4%
Fire strategy
Compartmentation, travel distances, suppression.
+2%
Acoustic engineer
Noise assessments for glazing + party walls.
+1.5%
5 External envelope specification
Select wall, roof and glazing performance.
Wall construction
Standard cavity wall
Block + insulation + brick
Enhanced insulation
Better U-values, reduced bridging
SIPs / timber frame
MMC systems or factory-made panels
Passivhaus-ready
Ultra-low U-value, airtight
Roof construction
Standard pitched
Typical insulation layers
Warm roof upgrade
Continuous insulation above rafters
High-spec flat roof
Warm deck + tapered insulation
Premium low-energy
Ultra-low U-value, airtight design
Window performance
Double glazing
Standard performance
High-spec double
Thermally broken frames
Triple glazing
Low thermal + acoustic transfer
Glazing amount
6 Structural complexity
Load alterations, beams, foundations, geometry.
Standard
Minimal structural alterations
Moderate
Several beams, deeper foundations
Complex
Multiple beams, heavy alterations
Very complex
Underpinning, irregular geometry
7 Finish quality
Internal material + fixture standard.
Standard
Good, economical specification
High
Upgraded sanitaryware + finishes
Premium
Designer fixtures, bespoke joinery
Luxury
Boutique, architectural finishes
8
Mechanical, electrical & plumbing
Optional upgrades to building services.
MVHR system
Mechanical ventilation with heat recovery
£3,500–6,000
Underfloor heating
Water-based UFH system
£35/m²
Full electrical rewire
Complete new circuits throughout
£4,000–7,000
Full plumbing upgrade
Pipes, manifolds, system overhaul
£3,500–6,000
Air source heat pump
Low-carbon heating system
£8,500–15,000
Solar PV array
Photovoltaic panels with inverter
£12,000–18,000
Battery storage
Energy storage for solar or off-peak
£6,000–10,000
10
Internal finishes
Flooring package
Engineered timber, LVT or tile allowances
£45/m²
Decorating package
Prep, prime and paint to all rooms
£25/m²
Bespoke joinery
Wardrobes, alcove units or built-ins
£4,000–10,000
11
External works
Landscaping
Patios, turf, planting
£6,000–12,000
Driveway / hardstanding
Block paving or resin
£3,500–8,000
Boundary fencing
Replacement closeboard or slatted
£2,000–4,000
12
Professional fees
Applied as percentages of construction cost.
Architect (8%)
RIBA stages 0–4 basic services
Architect + interiors (12%)
Full interiors & joinery design
Architect + full service (15%)
RIBA 0–6 with contract admin
13
Provisional sums & exclusions
Items often missed from early-stage budgets.
Contingency allowance (10%)
Industry standard risk allowance
+10%
Inflation allowance (6%)
Year-ahead tender adjustment
+6%
Strip-out works
Removes internal finishes, MEP systems & decoration
£2,000–4,000
Total project cost
£0
*excludes VAT
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