Why Foundations Are Provisional – And What That Means for Construction Costs

Deen Gabriel
3 days ago
2 min read

In building projects, foundations are often treated as provisional items in the Bill of Quantities (BOQ). This means their cost is not fixed at tender stage but subject to adjustment once actual site conditions are confirmed. Unlike finishes or fixtures, foundations depend heavily on ground realities, soil type, water table, rock layers, and unforeseen obstructions.

⚖️ Why Foundations Are Provisional

Uncertainty of Ground Conditions Even with geotechnical reports, soil conditions can vary across a site. Excavation may reveal soft spots, clay pockets, or unexpected rock that require deeper or reinforced foundations.
Risk Management By pricing foundations provisionally, contractors and estimators acknowledge that the scope may change. This protects both the client and builder from disputes when actual excavation differs from assumptions.
Flexibility in Design Engineers often adjust foundation design once excavation begins. Pile lengths, footing sizes, or reinforcement levels may increase, and provisional pricing allows for these changes without locking in unrealistic costs.

💰 Impact on Construction Costs

Treating foundations as provisional has direct implications for project budgets:

Initial Estimate vs. Final Cost The BOQ will carry a provisional sum, but the final cost is determined by measured quantities after excavation. This can lead to significant variation between tender price and actual expenditure.
Cash Flow Planning Clients and builders must allow contingency in budgets. A foundation that encounters rock excavation or groundwater management can add substantial costs early in the project.
Transparency in Pricing Provisional treatment ensures that variations are documented and priced fairly. It prevents underestimation at tender stage and provides a clear mechanism for cost adjustment.

🧭 Best Practices for Clients and Builders

Commission a Geotechnical Survey before tendering to reduce uncertainty.
Allow for Contingency in budgets, typically 10–15% of foundation costs.
Communicate Clearly with estimators and engineers about provisional sums and potential risks.
Monitor Excavation Progress closely to ensure variations are justified and documented.

✅ Conclusion

Foundations are the unseen backbone of any building, but their hidden nature makes them unpredictable. By treating them as provisional, estimators safeguard both client and contractor against unforeseen ground conditions. While this approach can lead to cost adjustments, it ensures fairness, transparency, and financial preparedness, key pillars of successful construction projects.