A Penthouse is typically an apartment on the highest floor of an apartment building. It usually takes up less than half of the entire (flat) roof of the building.[1] Originally the word penthouse meant a small building with a sloped roof.[2] The modern use of the word started in the 1920s in America. In the age of skyscrapers the "house" on the roof was called a penthouse.[2] A penthouse can also be commercial space.
Under some Building codes a penthouse cannot be more than one-third the size of the floor below it.[6] There is no limit to the number of penthouses a building can have. The only limit is the amount of space they can take up (one-third rule).[6] Also, some building codes do not allow mechanical or electrical equipment to count as a penthouse unless they are enclosed by a roof.[6]