Issues related to venting of attics and cathedral ceilings.

Current model building codes require attic ventilation in all U.S. climates. Originally, these requirements were strictly based on concerns for condensation in attics during winter in cold climates, and they were based on limited technical information. Nevertheless, attic ventilation has become the uncontested strategy to minimize condensation and ice dams during winter and extreme attic temperatures during summer. However, other strategies exist that address each of these problems as well as or better than attic ventilation. This paper examines issues such as summer attic temperatures, ice dams, and shingle durability and discusses the relative merits of attic ventilation compared to alternative design approaches in various climates. The authors support current recommendations for attic ventilation in cold and mixed climates but recommend that attic ventilation be treated as a design option in warm, humid climates. The authors review the new information on attic and roof ventilation in the 1997 ASHRAE Handbook Fundamentals and discuss the reasons for the changes.