A.Frank Vigil, senior
building science specialist at Advanced Energy in
Raleigh, N.C., responds: Dusting, sooting, or
ghosting — as these marks have all been
referred to — is not uncommon. Markings on
walls, carpeting, furnishings, even inside of
appliances, are all too common in today’s
houses, possibly because we’ve done
exactly what we set out to do years ago: build the
houses tighter. In tight homes —
especially tight homes with insufficient
ventilation — particulate has more
opportunity to deposit, instead of being flushed
away by regular air changes.
The dusting or staining that your homeowner is
experiencing requires two things in order to occur:
There must be a source for the material, and there
must be a driving force to cause the material to
deposit. A laboratory test of the material can be
helpful, at least to narrow the possible sources.
Is the staining gray, black, brown, or yellow? Does
it appear on places other than the carpet-to-wall
junctions? You mention that while the homeowners
don’t burn candles (so they claim), they
do have a gas furnace. Has the furnace been tested
for draft under the worst-case scenario (with
exhaust fans, clothes dryer, and central vacuum
cleaner operating)? Is there a woodstove or
fireplace (gas or wood)? Investigations over the
years have found all of these things can be
culprits for staining.
The driving force for stains along the
carpet-to-wall junction are typically pressures
caused by mechanical fans and/or stack effect (heat
rising). Air will always seek the path of least
resistance. If the house is pressurized, escaping
air will often go up the wall cavity to the attic.
The carpet serves as a filter, scrubbing the air of
some of the contaminates. Over time, this is what
you see on the carpet. On the other hand, negative
pressures in the house could be causing attic air
to filter down the walls, with the carpet
again serving as a filter.
Pressure mapping of the house by a qualified
technician can easily pinpoint the pressure
dynamics the house experiences while fans are
operating. From there, you can begin to trace
likely sources for the stain.