Is an office building that is used to house the administration staff considered a PPE item?

Is an office building that is used to house the administration staff considered a PPE item? I am not sure if ''housing'' implies rented to staff for residential purposes, or rented to staff for administrative purposes, or simply used by admin staff in the production of income? I know that a building used in the production of income is PPE, but I am not too sure what it means to house admin staff? Any input will be extremely appreciated. If an office building used for rental to other, is that not considered investment property?