Garage floor make up

[roscopeco2000]

Hello I am converting our garage next year into a habitable room. The issue I have is the garage floor is at the same level as the main house. Will building regs let me over insulate the walls and roof to composate for the lack of insulation in the floor? If I have to insulate I would hopefully use the thin kingspan insulation 20mm and overboard with 22mm structural ply and have a step. I really don't want to exgavate the floor, the annoying thing is the main house doesn't have any floor insulation as 80s Bungelow. Thanks advice welcome 

[Onoff]

At least if you did dig the floor up the spoil can go straight out the garage door rather than traipsing through the house. Doesn't take too long once you get going. 

 

@oranjeboom dug down his whole house in order to properly insulate and build back up with wet UFH.