Final answer:
A vapor barrier should be installed on the warm side of the insulation to prevent warm, moist air from condensing on a cold surface, which can lead to mold and structural damage.
Step-by-step explanation:
In the context of building construction, when installing a vapor barrier, it should be placed on the warm side of the insulation. This placement prevents warm, moist air from inside a heated building (during the winter) or outside (during the summer) from reaching a colder surface where it could condense. Condensation can pose a variety of problems, including the potential for mold growth and structural damage. Therefore, the correct answer is B. To the warm side.
For example, in the winter, insulation is used to limit the conduction of heat from the inside to the outside. A vapor barrier on the warm side helps to prevent warm indoor air, which is often moist, from interacting with the cold outer layer and condensing, potentially compromising the effectiveness of the insulation.