"The flag is customarily flown all year-round at most public buildings, and it is not unusual to find private houses flying full-size flags.
Some private use is year-round, but becomes widespread on civic holidays like Memorial Day, Veterans Day, Presidents' Day, Flag Day, and on Independence Day.
On Memorial Day it is common to place small flags by war memorials and next to the graves of U.S. war veterans. Also on Memorial Day it is common to fly the flag at half staff, until noon, in remembrance of those who lost their lives fighting in U.S. wars."source: Wikipedia