Massachusetts Construction Supervisor License (CSL) Practice Test

In a single family dwelling, how much should a 6 mil vapor barrier be lapped when placed between the base course and the concrete floor slab?

1. 4 inches

2. 6 inches

3. 8 inches

4. 10 inches

The correct answer is: 6 inches

The recommended amount for lapping a 6 mil vapor barrier in a single-family dwelling when placed between the base course and the concrete floor slab is 6 inches. This measurement is significant because it ensures sufficient overlap to effectively limit moisture transmission between the ground and the slab. Proper lapping helps in creating a continuous barrier, reducing the chances of mold growth and damage to the structural integrity of the home. It is crucial for maintaining indoor air quality and ensuring durability within the building. A barrier that is properly lapped not only conforms to best practices for moisture control but also aligns with building code requirements, which emphasize effective moisture management in foundation designs. Other lap measurements, such as 4 inches or more than 6 inches, are either insufficient for effective moisture control or unnecessary, as they do not improve the barrier's effectiveness.