There is no legal requirement for a minister to substantiate (or report) housing expenses to the church-period! In fact, you don't even have to report your housing expenses to the IRS-as strange as that may seem.
A housing allowance designation must be made prospectively for a pastor-generally before the church year begins, although amendments to the designation can be prospectively made mid-year.
This designation is based on projected housing expenses. The church has no obligation to match actual and projected housing expenses. It is the minister's responsibility to determine actual housing expenses for purposes of applying the housing allowance exclusion limitations.
The housing allowance designation and exclusion are separate issues. The church handles the designation issues and the minister cares for the exclusion matters.
Dan Busby is a certified public accountant, president of the Evangelical Council for Financial Accountability (ECFA), and the author of the Zondervan Clergy Tax & Financial Guide.