Title 4, United States Code, Chapter 1
As Adopted by the National Flag Conference, Washington, D.C., June 14-15, 1923, and Revised and Endorsed by the Second National Flag Conference, Washington, D.C., May 15, 1924
6. Time and occasions for display
(a) It is the universal custom to display the flag only from sunrise to sunset on buildings and on stationary flagstaffs in the open. However, when a patriotic effect is desired, the flag may be displayed 24 hours a day if properly illuminated during the hours of darkness.
(b) The flag should be hoisted briskly and lowered ceremoniously.
(c) The flag should not be displayed on days when the weather is inclement, except when an all weather flag is displayed.
7. Position and manner of display
(e) The flag of the United States of America should be at the center and at the highest point of the group when a number of flags of States or localities or pennants of societies are grouped and displayed from staffs.
(f) When flags of states, cities, or localities, or pennants of societies are flown on the same halyard with the flag of the United States, the latter should always be at the peak. When the flags are flown from adjacent staffs, the flag of the United States should be hoisted first and lowered last. No such flag or pennant may be placed above the flag of the United States or to the U.S. flag's right.
(h) When the flag of the United States is displayed from a staff projecting horizontally or at an angle from the window sill, balcony, or front of a building, the union of the flag should be placed at the peak of the staff unless the flag is at half-staff. When the flag is suspended over a sidewalk from a rope extending from a house to a pole at the edge of the sidewalk, the flag should be hoisted out, union first, from the building.
(i) When displayed either horizontally or vertically against a wall, the union should be uppermost and to the flag's own right, that is, to the observer's left. When displayed in a window, the flag should be displayed in the same way, with the union or blue field to the left of the observer in the street.
(j) When the flag is displayed over the middle of the street, it should be suspended vertically with the union to the north in an east and west street or to the east in a north and south street.
8. Respect for flag
No disrespect should be shown to the flag of the United States of America; the flag should not be dipped to any person or thing. Regimental colors, state flags, and organization or institutional flags are to be dipped as a mark of honor.
(a) The flag should never be displayed with the union down, except as a signal of dire distress in instances of extreme danger to life or property.
(b) The flag should never touch anything beneath it, such as the ground, the floor, water, or merchandise.
(c) The flag should never be carried flat or horizontally, but always aloft and free.