tip of the Heavens hat to Medford, Pa., architect
Charles J. Collins Jr., ably assisted by Joe Ponessa,
for helping to solve a riddle from a few weeks back:
sooty marks on walls above electric baseboard radiators.
has inspected many homes and has renovated houses with
similar stains at or near the intersection of wall and
meaning myself, my consulting mechanical engineer and my
home inspector have all concluded that the stains are
the result of the temperature differential between the
well-insulated wall cavity and the poorly insulated wall
plates that allows a condensation accumulation …. and
then attracts dust," he said.
has found a wealth of Internet articles about stains
above baseboard radiation that "do not seem to
reference the burning of dust but rather the same type
of attraction of dust due to condensation."
called "ghosting," according to what Collins
has found. He sent this snippet from an article that
often occurs higher up on the ceiling, but the cause
could also be present just above the baseboard. The
combination of humidity in the house plus cold spots on
the walls/ceilings attracts the moisture. Then dust in
the air inside the house gets stuck to these moist
professor emeritus Ponessa said the phenomenon is called
"shadowing," usually attributed to the fact
that, in a standard wall assembly, the studs are
typically colder during the heating season than the
adjacent insulated wall cavity.
physical theoretical explanation has something to do
with the soot particles, bounding around in the air ….
are slowed down at the colder areas, and somehow settle
there," Ponessa said. "Another possibility is
that moisture condensation on cold spots on the wall
promotes mold growth."
way to prevent shadowing or ghosting is to cut the
temperature differential, say through insulation or air
a fuller explanation, Ponessa sent this link to Joe
Lstiburek’s fact sheet, "BSD-150: Black Stains on
Carpets and Ghosting of Framing," at