I'm a pastor and own a home. We took a loan to replace windows on our home. Contract signed in Dec 2018. Can I take the total cost off from housing allowance in 2018?

All the windows will be replaced in 2019. The contract to do the windows was signed in December 2018. I am a pastor who qualifies for housing allowance. Can I deduct the total of the window replacement from my housing allowance as a one-time deduction in 2018?