Final answer:
Foam plastic inside a building should be separated from the interior by an approved thermal barrier of gypsum board.
Step-by-step explanation:
The question pertains to the requirement for an approved thermal barrier for foam plastic inside a building. According to building codes, foam plastic should be separated from the interior of a building by an approved thermal barrier of gypsum board.
The thickness of the gypsum board required would depend on the specific building code, but commonly it is in the range of 1/2 inch to 5/8 inch.