How to reduce floor level in garage conversion

[Momo2021]

Hello,

I’m am hoping on extending my living room into my integrated garage at the side of my house next year .
My house has already been extended in 2007 which included a bathroom and bedroom upstairs and a living room and garage downstairs .
My ceiling downstairs from living room to garage is running at the same hight but when measuring my floor level down from the first floor joist I have a 70mm discrepancy from living room to garage.
Now I’m pretty sure that garage subfloors tend to be lower than the house for petrol leaks etc. but my garage floor is 70mm higher!
I would obviously like to have the floor running level all the way through the living room without having a 70mm step.
Has anyone ever come across this or has anyone any idea why this would be the case and how I would lower the concrete floor in the garage?

Thanks Mo

 

[darkkent8]

Not sure why it would be higher - but it would be a case of digging it all out down to a height where you can insulate and pour concrete on top - or dig down enough to build a sub floor.
i think the regulations are 100mm insulation and 100mm concrete - so if you dig down 270 and you have a good sub base you can go from there - or you need to go lower and put some type 1 down as first