Historic Tax Credit Improvement Act of 201 7 This bill amends the Internal Revenue Code, with respect to the tax credit for the rehabilitation of buildings and historic structures, to: (1) allow an increased 30% credit, up to $750,000, for projects with rehabilitation expenditures not exceeding $3.75 million, for which no credit was allowed in either of the two prior taxable years (smaller projects); (2) allow the transfer of tax credit amounts for smaller projects; (3) treat a building as substantially rehabilitated if rehabilitation expenditures exceed the greater of 50% of the adjusted basis of the building or $5,000 (currently, the greater of the adjusted basis of the building or $5,000); (4) reduce the required basis adjustment from 100% of the credit to 50% of the amount of the credit; and (5) limit the application of disqualified lease rules to tax-exempt use property.