Is your friend's house in same climate and soils?

A slab can be better for radiant heat in slab. Some places concrete finishers are hard to find. Some places require deeper footings, Some people prefer the comfort of a wood framed floor. Cost can enter the mix.

Thanks for your reply!

We both live in western chicago suburbs, in towns 20 miles apart. Both neighborhoods have trilevels, and ranch style homes primarily. My house was built in 1976 and his late 1960's. All homes in his subdivision have crawl spaces, mine slabs. The crawl space is creepy to me, there are animals in there. The slab seems so much ... nicer. Thanks, Joan

Slab on grade was relatively uncommon in the north until only a few years ago when frost protected shallow slab foundations were developed as a building method.

By putting some things in the crawl space, such as the water heater, you save floor space in the house.