Department of Housing and Urban Development investigators found no evidence that Secretary Ben Carson acted improperly when he tried to buy a $31,000 dining room set for his office in 2017, according to an inspector general’s report released on Thursday.

The inspector general determined that Mr. Carson and senior department staff members did not follow federal laws that prohibit expenditures of more than $5,000 on office furniture without congressional approval when he signed off on the purchase of a custom table, chairs and hutch to replace a worn-out set.

Investigators placed blame for the episode not on Mr. Carson, who told them he “seemed” to have knowledge of the requirement, but on department officials who “were aware of the law” and “either failed to consider or didn’t understand” that it applied to the purchase, according to the 14-page report.

The decision to proceed reflected a historic lack of “adequate internal controls” on purchasing at the department, Rae Oliver Davis, the inspector general, concluded after a yearlong investigation.