Provisional sums are a widely used mechanism in construction contracts, particularly within commercial projects where full design information is not available at the time of tender.

They act as financial allowances for elements of work that cannot yet be fully defined, measured, or specified.

While they are useful, they also introduce uncertainty that must be carefully managed.

Why Provisional Sums Are Used

Provisional sums are typically included when:

  • Design information is incomplete
  • Specialist input is still required
  • Client decisions are pending
  • Site conditions are uncertain
  • Further investigation is needed

They allow projects to proceed without delaying procurement, but they should always be treated as temporary allowances.

Defined vs Undefined Provisional Sums

Defined Provisional Sums

These are supported by sufficient detail to allow contractors to reasonably assess:

  • Scope of works
  • Construction methodology
  • Programme implications
  • Cost assumptions

They carry lower risk and greater cost certainty.

Undefined Provisional Sums

These are based on limited or unclear information, often resulting in:

  • Wide cost variation between contractors
  • Greater uncertainty in final cost
  • Higher risk of disputes
  • Difficulty in programme planning

Undefined sums should be minimised wherever possible.

Risks of Poorly Managed Provisional Sums

If not properly controlled, provisional sums can create significant project challenges, including:

  • Budget escalation beyond initial forecasts
  • Frequent contract variations
  • Delays due to scope clarification
  • Misalignment between client expectations and delivery
  • Increased contractual disputes

These risks often increase as projects progress into construction without full definition of scope.

How to Improve Cost Certainty

Reducing reliance on provisional sums is key to improving project certainty. This can be achieved through:

  • Earlier and more detailed design development
  • Improved coordination between consultants
  • Contractor involvement during preconstruction stages
  • Clear definition of scope before tender
  • Risk reduction workshops and planning sessions

The more clarity achieved before construction begins, the more reliable the cost plan will be.

Conclusion

Provisional sums are a necessary part of many construction contracts, but they must be carefully controlled.

Effective management leads to:

  • Greater cost certainty
  • Reduced project risk
  • Improved programme reliability
  • Fewer disputes during construction

Clarity at the early stages always leads to better outcomes later