One way to convert a barn into a home is to use permitted development rights.
Class Q is the name given to the permitted development right to convert agricultural buildings into dwellings which have been with us since 2014.
Permitted development is the right of an owner to develop his or her land within limits prescribed by the General Permitted Development Order. The point of the order was originally to allow minor development to go ahead without having to go through the planning application process. For example small extensions to houses and simple changes of use i.e. changing a pub to a restaurant or a bank to a shop.
In the interest of simplifying the planning system and boosting the supply of houses, the government extended permitted development rights to include the right to change agricultural buildings to dwellings.