The classification of a Listed building, is any building or structure built before the 1700’s, or between 1700 and 1840, that is in good condition or close to original condition and that has been listed as interesting either historically or architecturally.
There are newer listed buildings, but for anything built after 1940 the building has to be very important or unique for it to be put forward as a listed building and has to be at least 30 years old to even be considered for listing. Listed buildings are graded as to historical importance, grade I, grade II*, and grade II. Read more »