Standards of Proof - A Brief Resource for Construction Claims

The standard of proof should be distinguished from the question of who bears the burden of proof. In civil actions, including construction claims arising from delay or acceleration, the standard of proof is relaxed to "a preponderance of the evidence". The preponderance standard simply means that the proponent of a claim must present the greater weight of the competent, persuasive evidence, even if that is only 51% of the evidence.
One further distinction that has been drawn by the courts and boards touches on the quantum of proof required for causation of delay, and the quantum of proof relating to the amount of damages. Generally, a greater certainty is necessary for proof of the causation of delay than for proof of the amount of damages.
The U.S. Court of Claims has held, in Wunderlich Contracting Co. v. United States, 351 F.2d 956, 173 ct. cl. 180 (1965) :

A claimant need not prove his damages with absolute certainty or mathematical exactitude. It is sufficient if he furnishes the Court with a reasonable basis for computation, even though the result is only approximate. Yet this leniency as to the actual mechanics of computation does not relieve the contractor of the essential burden of establishing the fundamental facts of liability, causation, and resultant injury.

See also Dale Construction Co. v. United States, 161 ct. cl. 825 (1963).
Once entitlement is established, damages will not be refused solely because the contractor has not proved their amount to a mathematical certainty. Most courts and boards are willing to accept a reasonable estimate or a logical method of calculation.
See: Peter Kiewit Sons Co. v. Summit Construction Co., 422 F.2d 242 (8th Cir. 1969; and Lauria Bros. & Co. v. United States, 369 F.2d 701 (1966).