@Carl is correct; the depreciation period is 39 years, not 27.5.
Reference: https://www.bankrate.com/finance/money-guides/home-office-can-have-hidden-tax-costs-1.aspx
“The depreciation life of your home office is 39 years, since it’s business,” says the Illinois CPA. The IRS has determined the costs associated with business real property must be spread out, i.e., depreciated, over that time period. But often, home office taxpayers misread the rules".
“Many people use the 27.5-year residential property schedule since the office is in their home,” says Tollaksen. “But in the IRS’s eyes, it’s a business regardless of its physical location, so business tax rules apply.”
