Insulating/ventilating outbuilding

[dragonflyy]

I have an old washroom attatched to the house that is 6ft 1 x 8ft The room has a window, radiator and electric.. single skin walls 3 of which are outside with one airbrick. i'm wanting to turn it into a bedroom... What would need to be done? and where would I start

 

[Deluks]

By the time time you've insulated the walls to the required spec, you won't get a bed in there.