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