Valuation of federal property — Real estate included; return to Congress.

There shall be a valuation taken of all real estate belonging to the United States in the District, except the public buildings, and the grounds which have been dedicated to the public use as parks and squares, at least once in 5 years, and return thereof shall be made by the Commissioner of the District of Columbia to the President of the Senate and Speaker of the House of Representatives on the first day of the session of Congress held after such valuation shall be taken.