What problem can occur if a vapor-resistant paper is used over sheathing?

Using vapor-resistant paper over sheathing can lead to the accumulation of moisture within the wall assembly. Vapor barriers are designed to prevent water vapor from passing through them, which means that if moisture occurs within the wall cavity due to air leaks, humidity, or other factors, it can become trapped. This trapped moisture can condense and lead to a range of issues, including mold growth and wood rot over time, as the moisture cannot escape. Proper ventilation and the appropriate use of vapor barriers are essential in construction to ensure that moisture is managed effectively within a building structure.

In contrast, using a vapor-permeable material in conjunction with appropriate ventilation strategies allows for moisture to escape, thus preventing the issues associated with accumulation. This highlights the importance of understanding the building envelope and how moisture moves within it in order to make informed decisions about materials for optimal building performance.