Rarely is a home office depreciated over 27.5 years. Here's what in IRS Pubplication 946
Office in the home.If your home is a personal-use single family residence and you begin to use part of your .home as an office, depreciate that part of your home as nonresidential real property over 39 years (31.5 years if you began using it for business before May 13, 1993). However, if your home is an apartment in an apartment building that you own and the building is residential rental property, as defined earlier under Which Property Class Applies Under GDS, depreciate the part used as an office as residential rental property over 27.5 years. See Pub. 587 for a discussion of the tests you must meet to claim expenses, including depreciation, for the business use of your home
