Grandfather clause

A grandfather clause is an exception, originating from the United States, that allows a pre-existing rule to remain as it is despite a change in the rules applied to newer situations. It is often used as the verb "to grandfather in".

Examples from the US

• The 22nd Amendment to the United States Constitution specified term limits for future presidents, but did not apply to the president (Truman) in office when Congress passed it.
• Fire sprinklers are required in all new buildings – but due to the great expense of having older ones retrofitted, they are generally exempt unless and until they are renovated. Such an exception proved deadly to 100 people in 2003 at the Station nightclub fire in Rhode Island, and gutted a large part of an older high-rise office building in the Peachtree 25th fire in Atlanta in 1989.
• Zoning laws often grandfather in existing buildings or other uses, such as when an area is rezoned from residential to commercial, and the existing home on the lot need not be torn down or converted.
• Existing toll roads were allowed to become part of the Interstate highway system in the U.S., even though no new Interstates could (at the time) have tolls.
• Early Internet RFCs which were de facto standards were grandfathered into the official IETF Internet standard process.
• The FCC has required all radio stations licensed in the United States since the 1930s to have four-letter callsigns starting with a W (for stations east of the Mississippi River) or a K (for stations west of the Mississippi River). However, stations with three-letter callsigns and stations west of the Mississippi River starting with a W (plus KDKA, KQV and KYW in Pennsylvania) licensed before the 1930s have been permitted to keep their callsigns.
• In the 1970's, WTBS in Atlanta, Georgia, which broadcast Atlanta Braves baseball games, became a Superstation, allowing people outside the Atlanta market to view Braves games. With certain rules in effect by Major League Baseball, teams are no longer allowed to be broadcast out of market unless available in a package.
• Major League Baseball retired the number 42 worn by Jackie Robinson in 1997 in remembrance of the 50th anniversary of his first MLB appearance, which broke the sport's 20th-century color line. Players who wore #42 at that time were allowed to continue wearing the number for the remainder of their careers; the most notable player affected by this clause is Mariano Rivera, who is now the only player still wearing the number.
• The National Football League mandates that ownership groups of its franchises have no more than 10 members, and that one owner have at least 30% ownership. When the NFL established this policy, it grandfathered in the unique community-based ownership scheme of the Green Bay Packers, in which thousands of individuals owned shares. The Packers made a second stock offering in 1997 and 1998, which expanded the number of owners to over 100,000. Currently, no individual owner may hold more than 200,000 of the roughly 4.8 million Packers shares outstanding.
• The NCAA has banned artificial surfaces for football whose color is anything other than green. However, Boise State University is allowed to retain the unique blue artificial surface at Bronco Stadium, which it had installed several years before the NCAA ruling.