Contingency & Unknowns
Understanding why projects have contingency budgets and what they're for. Building work reveals surprises—be prepared financially.
What Is Contingency?
Contingency is a percentage of the project budget set aside for unexpected costs. Professional projects typically include 10-15% contingency. It's not "padding" or profit—it's realistic budgeting for the unknowns inherent in construction work.
The Reality of Construction
You can't know what's hidden inside walls, under floorboards, or beneath the ground until you open it up. A simple bathroom renovation often reveals:
- Rotten joists under old flooring
- Dodgy electrics requiring replacement
- Damp that needs treatment
- Structural issues (cracked walls, settling)
- Outdated plumbing that needs full replacement
- Asbestos or other hazardous materials
These aren't failures—they're the reality of building work. Professional contractors expect and budget for them.
Why Contingency Matters
1. Protects your budget: When hidden issues emerge (and they will), you have funds to address them without stalling the project.
2. Prevents cheap fixes: Without contingency, you might be forced to use substandard solutions. Contingency allows proper repairs.
3. Keeps projects on track: No contingency often means projects stall while you fundraise for unexpected issues.
4. Maintains quality: Proper contingency means work continues at proper standard, not "make do" solutions.
5. Contractor protection: Good contractors expect contingency. No contingency means contractor assumes all risk—they charge accordingly.
Typical Contingency Percentages
10-12% Contingency
Straightforward, low-risk projects
Example: New kitchen in modern home (minimal hidden issues likely)
12-15% Contingency
Standard approach for most projects
Example: Bathroom renovation, cosmetic work, modern properties
15-20% Contingency
Higher-risk projects needing protection
Example: Listed buildings, period properties, structural work, older homes
20%+ Contingency
Very high-risk or exploratory work
Example: Subsidence repairs, major structural issues, properties requiring extensive investigation
Common Hidden Costs
Damp & Water Issues
Rising damp: £2,000-8,000 (physical damp proof course installation)
Penetrating damp: £1,000-5,000 (repointing, waterproofing)
Condensation: £500-2,000 (ventilation upgrade)
Very common in older properties. Often discovered during renovation.
Structural Issues
Rotten joists/timber: £2,000-10,000+ (replacement, structural repairs)
Cracks/subsidence: £5,000-50,000+ (investigation, repairs, underpinning)
Settlement issues: £3,000-20,000 (repairs, monitoring)
Often only discovered when opening walls. Professional investigation required.
Hidden Systems
Asbestos removal: £3,000-15,000+ (depends on extent)
Lead paint remediation: £1,000-5,000
Outdated wiring requiring replacement: £2,000-8,000
Hidden pipework requiring rerouting: £1,000-5,000
Pre-1980s homes often contain hazardous materials or outdated systems.
Ground & Foundation Issues
Contaminated ground: £5,000-50,000+ (investigation, remediation)
Soft ground/poor bearing: £3,000-20,000+ (ground stabilisation)
Tree root damage: £2,000-10,000 (underpinning, repairs)
Discovered during excavation for extensions or new foundations.
Access & Logistics Issues
Difficult site access: £1,000-5,000 (specialist equipment/methods needed)
Cannot park vehicle on site: £500-2,000 (additional transport costs)
Working in occupied property: £2,000-8,000 (slower work, protection, logistics)
Urban locations and period properties often have access challenges.
Real Project Example
Bathroom Renovation - Contingency In Action
Original Quote: £8,000
With 15% Contingency
What Actually Happened
- Day 2: Rotten joists found under old tile. Replacement needed: +£800
- Day 3: Old wiring unsafe, electrician recommends replacement: +£1,500
- Day 4: Discovered condensation issue, need specialist ventilation: +£600
- Total overrun without contingency: £2,900
With £1,200 contingency: The first two issues are covered. The third requires £600 from contingency, using £600 of the £1,200 buffer (leaves £600 remaining).
Without contingency: Project stops after £800 issue. You'd need to find extra £2,900 or accept substandard work.
How to Use Contingency Properly
1. Don't spend it upfront: Contingency is reserve—only spend if unexpected issues arise.
2. Get quotes for surprises: If something unexpected emerges, get a quote. Only approve if essential.
3. Keep records: Document what contingency was used for. Important for future reference and resale.
4. Unused contingency is yours: If the project comes in under budget, remaining contingency is your saving.
5. Don't let contractors raid it: Good contractors only use contingency for genuine surprises with your approval.
Common Misunderstandings
- "Contingency is contractor profit": No. It's a financial buffer for both parties. Properly managed, unused contingency goes to homeowner
- "Good planning eliminates contingency": No plan is perfect. Even well-planned projects have surprises
- "We can just use credit if issues arise": Risky. Contingency is planned budget—much better than emergency borrowing
- "If they're not using contingency, they're competent": Not necessarily. Most real projects have at least some contingency use
Red Flags
- Quote with no contingency mentioned: Unrealistic or unprofessional
- "Contingency not needed on this project": Every project has unknowns
- Contractor using contingency without asking: Should be approved by you first
- Vague about what contingency covers: It should cover "unforeseen costs"—be specific