Book excerpt: The inspection of insulation and ventilation systems is particularly challenging because so little of the systems can be seen. This text discusses how insulation, air/vapor barriers and ventilations systems work to keep houses comfortable and structurally sound. Basics of heat transfer and vapor movement are covered first to lay the groundwork for discussion of insulation and ventilation materials, systems, and applications. Thorough treatment of venting living spaces is provided, including balanced ventilation systmes and heat recovery ventilators (HRV's).