Final answer:
A vapor barrier is used beneath a concrete slab to prevent moisture from entering the heated space, serving a crucial role in both structural integrity and the efficiency of heat transfer.
Step-by-step explanation:
Vapor barrier or moisture barrier is placed over the gravel layer under a concrete slab to prevent moisture from entering the heated space. During construction, as explained by Beth, a wooden framework is used to shape the space for the slab, and then concrete is poured into this framework to form the slab. A vapor barrier is critical because it not only prevents moisture penetration, which can lead to structural damage but also, like thermal paste in electronics, it increases heat transfer by eliminating gaps, effectively enhancing the contact surface area between the concrete and the space above it. Ensuring that this barrier is in place is essential for maintaining the integrity and efficiency of the building structure and its heating systems.