“The Florida Building Code sets the standards for minimum size requirements, which vary depending on the designated occupancy and type of structure being built. For instance, a detached, single-family home in Florida must have at least 150 square feet of floor space, excluding bathrooms and closets. However, minimum sizes increase with each additional occupant, with at least 100 sq. ft. of additional space for each extra individual.”
That is not just in Florida. Years ago minimum living space, light,and ventilation was based on the Council of American Building Official’s 1&2 Family Dwelling code which was adopted either locally or by the state. I think the current code for 1&2 Family Dwelling is from the International Code Commission and adopted into statute. There are also housing codes which cover existing buildings.