I own a 2-flat building, rent out 1 apt. I am aware I could only write off 50% of the property. but can I claim as a small business?

[popa1125]

how to claim an as a small business on my property?

[ColeenD3]

To claim it as a business, you would also need to provide a service such as a motel (maid service) or a bed and breakfast (maid service and food). You don't need to however. You can claim your income and losses on Schedule E, and treat it as a business. You would be limited as to your losses but are potentially eligible to take the QBI deduction.

Rental Real Estate Safe Harbor As discussed in Notice 2019-07, a safe harbor is available to individuals and owners of pass through entities. Under the safe harbor, a rental real estate enterprise will be treated as a trade or business for purposes of the QBI deduction. Taxpayers may still treat rental real estate that doesn’t meet the requirements of the safe harbor as a trade or business for purposes of the QBI deduction if it is a section 162 trade or business.