For the past year I've been conducting an informal survey about "hot roofs" — unvented cathedral ceilings in which the rafter cavities are packed full with insulation. Who is building them and why? When do problems occur and why? From Anchorage to Atlanta, the responses have been remarkably consistent. Hot roof fans claim there will never be problems as long as the entire rafter cavity is packed full with insulation and protected against moisture intrusion. Most use blown-in insulation rather than batts. One such system, Ark-Seal's Blow-In-Blanket (BIB), is particularly popular with hot roof advocates (see Figure 1). On the other side are the more conservative contractors who insist that without ventilation, a cathedral ceiling will suffer ice damming in cold climates, shingle