The housing allowance for Bi-vocational pastors is limited to their ministerial income received. Per, the IRS "if you get income for working as a minister who is an employee, count it as earned income. This income includes:
Wages
Salaries
Tips
Other taxable employee compensation"
The housing allowance would need to meet the following criteria:
the amount is officially designated as housing and allowance
the amount is actually used to provide or rent a home
or the fair market rental value of the home
See the following links for additional information: