Thirsty I believe Leo is correct. I have a granny flat. Currently unused. I went to get planning to convert the space into a two story extension to create a separate unit and I did not apply for it as such, just as an extension to the family home. I did that precisely because I knew I wouldn't get permission as a separate unit. It's what many people do. Just so you know. If you're selling you just don't sell it as a separated house. (that's why you make sure you have an internal way to get into it (in my case I plastered up the door, neither the house nor the flat know it exists there behind the cooker !). I've often seen houses being sold with granny flats but the majority of them have no planning. As my flat is now there more than 20 years there is nothing the council can do to me about it. Others, like Leo, would not counsel people to go down this route. You'll find it next on impossible to get permission though. (Leo might confirm). Rent a room As long as the structure is part of the house, ie basement flat or converted attached garage it qualifies. A chalet in the garden does not.