@Joshua Davies
As per IRS, rental income will be taxed depends on whether or not the foreign person who owns the property is considered "engaged in a U.S. trade or business." Ownership of real property is not considered a U.S. trade or business if it consists of merely passive activity such as a net lease in which the lessee pays rent, as well as all taxes, operating expenses, repairs, and interest in principal on existing mortgages and insurance in connection with the property. Such passive rental income is subject to a flat 30 percent withholding tax (unless reduced by an applicable income tax treaty) applied to the gross income rather than the "net rent" received. Thus, the real estate taxes, operating expenses, ground rent, repairs, interest and principal on any existing mortgages, and insurance premiums paid by the lessee on behalf of the foreign owner-lessor, must be included in gross income subject to the 30 percent withholding tax. The gross income and withheld taxes must be reported on Form 1042-S, Foreign Persons U.S. Source Income Subject to Withholding to the IRS and the payee by March 15 of the following calendar year. The payor must also submit Form 1042, Annual Withholding Tax Return for U.S. Source Income of Foreign Persons, by March 15.
