Building Science-Ghosting

Indoor air quality can effect a lot of things, of course the biggest is people’s health.  How do you know if you have poor indoor air quality?  One possible indicator is a phenomenon known as ghosting.

Ghosting is dark lines or staining on walls and ceilings on the interior of a home.


Looking closely at the above photo, you can clearly see every stud and drywall fastener in the wall.  Drywalled ceilings can have a similar appearance.

What is the cause of the discoloration?  During the winter months, the framing members (studs or rafters) are a thermal bridge from the cold exterior to the warm interior of the home.  These colder areas tend to attract the fine particulates (indoor air pollution) from burning candles, cigarette smoking, or a home that is heated by wood heat where smoke occasionally ends up inside the home.

You can also see some larger areas of discoloration in the corner.  I did not perform a blower door test of this home, but my guess is that the outside corner of the home has an air leak to somewhere inside.  This air leak was probably made worse by burning wood in the fireplace that uses inside air for combustion, thus causing a negative pressure within the home when the heated air moves up the chimney to the outside.  These air leaks cooled the drywall in larger areas causing this staining.

A temporary solution is to scrub the effected areas or apply a fresh coat of paint.  A more permanent (and much more expensive) solution is to fix the thermal bridging issues.  The reason I was at this home in the first place was because of a winter time high heating cost.  Fixing the thermal bridging should also reduce these costs.

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