This is an action brought by one Sesto, a sewer contractor, to recover from the city of Omaha for lumber used to brace the ditch during the period of construction, which was left in 'the excavation permanently according to the contractor’s allegation, under the direction of the city engineer. The city of Omaha appeals from a judgment in favor of the claimant.

One question presented by the case relates solely to a question of fact as to whether or not the city engineer by his authorized representative, the city sewer engineer, ordered the contractor to leave the lumber in the ditch. Upon this question the evidence is in conflict. The finding of the trial court, a jury having been waived, based upon abundantly sufficient evidence to support it, will not be disturbed on appeal.

In the other question presented by the city, it seeks a construction of several paragraphs of the contract. It is seriously and energetically urged that the contract provides that extra work in connection with the construction shall be done, when the engineer especially directs such *731work in writing. We are of the opinion that the use of some lumber is anticipated and specific provision made for it in another paragraph. However, this case is determined upon the principle that, where a contract is so ambiguous as to require construction, and the parties, with a knowledge of its terms, themselves have given it a practical construction by their conduct thereunder, such construction is entitled to great weight as a certain indication of their true intent and, although not controlling, courts will generally enforce such construction. Cady v. Travelers Ins. Co., 93 Neb. 634; Hale v. Sheehan, 52 Neb. 184; Jobst v. Hayden Bros., 84 Neb. 735; State v. Board of County Commissioners of Cass County, 60 Neb. 566. In this case the city recognized that the contractor was entitled to pay for some lumber, although not ordered in writing. In recognition thereof, it paid him for 2,976 feet which Sesto mistakenly thought at the time of payment was for all the lumber, instead of the 29,786.67 feet, stipulated by the parties as having been left in the ditch. In this action he is met for the first time with a refusal to pay because the order was not in writing. The parties had thus placed a practical construction upon the contract, which should be followed by the court.

The finding and judgment of the trial court is

Affirmed.