Comprehensive Guide to Accurate Project Budgeting | ashton-paul.co.uk | 07736 733326
How to Use This Calculator
Fill in your project dimensions and preferences, then add up totals for your overall budget. Based on 2025 London rates. Always add 10-15% contingency.
Ensure every detail is specified before requesting builder quotes:
External Materials
Bricks (type, colour, manufacturer)
Roof tiles/felt (type, colour, pitch)
Windows (material, colour, style, glazing)
External doors (material, style, security)
Gutters & downpipes (material, colour)
Fascias & soffits (material, colour)
External wall insulation (type, U-value)
Internal Structure
Structural steels/RSJs (sizes, locations)
Foundation type (depth, width)
Floor construction (concrete/suspended)
Ceiling heights
Internal wall construction
Roof structure (flat/pitched, insulation)
Internal Finishes
Wall plastering (skim/plasterboard)
Floor finish (tiles/wood/carpet, style)
Ceiling finish (plaster/suspended)
Skirting boards (style, height, material)
Architraves (style, material)
Internal doors (style, material, furniture)
Paint colours (walls, ceilings, woodwork)
Kitchen
Unit style & finish (manufacturer, range)
Worktop material (type, colour, edge)
Sink & tap (style, finish, make)
All appliances (make, model, dimensions)
Handles & hinges (style, finish)
Splashback (tiles/glass, size, colour)
Electrical
Consumer unit upgrade required?
Socket types & positions (layout)
Light fittings & positions (schedule)
Switch styles (finish, type, dimmers)
USB charging points
TV/data points
External sockets/lighting
Smoke/CO detectors
Plumbing & Heating
Radiator types & sizes (each room)
Radiator valve style (TRVs, finish)
Boiler upgrade (make, model, location)
Underfloor heating? (type, zones)
Hot water cylinder upgrade?
Waste & drainage routes
Water supply positions
External Works
Patio/decking (material, size, design)
External drainage (foul & surface)
Landscaping (fencing, paving, planting)
External lighting
Bin store/utility area
6. Provisional Sums: Warning Guide
Provisional sums are placeholders when you haven't specified exact products. Major source of budget overruns.
Item
Typical Provisional
Realistic Cost
Shortfall Risk
Kitchen
£10-15k
£21-35k
£6k-£20k
Electrics
£3-5k (50pts)
£8-10k (80-100pts)
£3k-£5k
Flooring
£1.5-2k
£2.5-4k
£1k-£2k
Bathroom
£3-5k
£6-12k
£3k-£7k
Windows/Doors
£2-3k
£4-8k
£2k-£5k
TOTAL SHORTFALL RISK
£15k-£39k
⚠️ Actions: (1) Request detailed breakdown of all provisional sums (2) Ask what's included/excluded (3) Get actual costs BEFORE accepting quote (4) Add 20% buffer on unspecified provisionals (5) Specify everything possible to eliminate provisional sums
7. Contingency Planning Worksheet
Potential Additional Costs
Probability
Your Budget
HIGH PROBABILITY (60-90%)
Unforeseen ground conditions (tree roots, old foundations)
60-80%
£______
Additional structural work during demolition
50-70%
£______
Building control additional requirements
40-60%
£______
Design changes requested during build
70-90%
£______
MEDIUM PROBABILITY (20-50%)
Services relocation (gas, electric, water mains)
30-50%
£______
Drainage issues or connection upgrades
30-50%
£______
Party wall complications/delays
20-40%
£______
Weather delays (winter builds)
40-60%
£______
Material price increases during project
30-50%
£______
LOW PROBABILITY (1-20%) - HIGH COST IF OCCURS
Asbestos discovery & removal
10-20%
£______
Archaeological findings / Neighbour disputes / Major structural defects
Book consultation with architect/design & build firm
Discuss budget, requirements, feasibility
Commission measured survey (if required)
Receive & refine design concepts
Finalize planning drawings
Submit planning (if required) or confirm permitted dev
Phase 2: Detailed Design (Weeks 9-16)
Receive planning approval (8 weeks)
Commission structural calculations
Prepare & submit building control
Visit kitchen & bathroom showrooms
Select all finishes (use Section 5 checklist)
Create detailed specification
Finalize electrical and plumbing layouts
Phase 3: Procurement (Weeks 17-20)
Request quotes from 3+ builders (identical specs)
Review & compare quotes (check provisionals!)
Interview builders, check references
Select preferred contractor
Review & negotiate contract terms
Arrange party wall agreements (if required)
Sign building contract & finalize schedule
Phase 4: Construction (Weeks 21-32)
Pre-construction meeting
Groundworks & foundations (wks 1-2)
Structural frame & walls (wks 3-5)
Roof & weatherproofing (wks 5-6)
First fix: electrics, plumbing (wks 7-8)
Plastering & finishes (wks 9-10)
Second fix: kitchens, bathrooms, flooring (wks 10-11)
Decorating & snagging (wk 12)
Building control final inspection & handover
💡 Prefer All-in-One? Ashton Paul's design & build service handles everything. 37 years experience. Fixed-price contracts, no hidden costs, full specification included, single contact throughout, accurate costs from day one. 📞 07736 733326 | 🌐 ashton-paul.co.uk/book