Everything I read implies you would always want to insulate the floor when converting an internal garage to a room. My 50's bungalow has a garage where the floor is level with the house floor (the exterior garage walls are also cavity walls). It seems highly likely that it was made as a single slab, so its insulation is no better or worse than the rest of the house.
I do not want to put insulation on top of the garage floor and have a step up into the new room. That would make the ceiling low and would make fitting the door difficult. Never mind the trip hazard from a step. I also don't want to dig out the floor and put in a new insulated floor, when all that would do is give 15% of the house better floor insulation.
Do Building Regulations mandate that I have to insulate the floor, even though it would be pointless?
I thought that might be the case. Is it a big job to dig out a floor to put insulation underneath? Not a pleasant job, I'm sure, but is it just a case of angle grinding round the edge and breaking up the middle?