Illinois Home Inspector Practice Exam 2026 - Free Home Inspector Practice Questions and Study Guide

The recommended maximum indoor humidity level to effectively prevent mold or spore development is typically around 60%. Mold thrives in environments where humidity levels exceed this threshold, as excess moisture provides an ideal breeding ground for mold spores. Maintaining indoor humidity at or below 60% helps to inhibit mold growth and promotes a healthier living environment.

Humidity levels higher than this can lead to not only mold growth but also potential damage to building materials and furnishings, and can contribute to health issues such as respiratory problems. Therefore, keeping indoor humidity controlled at or below this level is essential for mold prevention, making the choice of 60% the appropriate answer in the context of indoor air quality and health considerations.