I have a Slab on grade house, there was a 10 foot extension added on the
rear of the garage which I want to add anotehr four feet, Also add second
floor above for office. The extension and garage are lower than the main
florr of the house, however I would like to have the extension to the rear
of the garage and the addtional four feet that I am wanting to add be the
same level as the rest of the house as I will need to remove all the
originall roof and walls on the existing extension anyway.

What are the issues with having new slab foundation added and concrete
pourded over existing slab assuming the existing slab foundation is
suffiencient to support a second floor above ?

We are planning new laundry, bath and storage space in this new area on
first floor.

Thanks,
MC