Isolation

Isolation refers to how "well-surrounded" a building is, usually referring to its walls and ceiling. A good isolation helps block out noise caused by doing some tasks or jobs. Adding doorways (which are necessary for citizens to enter the building) will not decrease isolation. If any walls are removed from a building, isolation will decrease.

In-game description

"Isolation prevents room degrade and sound pollution. Achieved by surrounding rooms with walls and a few doorways."