What Can We Tell from This Photo? (Case Study 12)

Posted by in Apparent Mold/Biological Growth, Simple Forensic Methods | November 30, 2015

What does this photograph show?

This photograph was taken of active condensation of excessive airborne moisture on the underside of a roof deck.  This photograph provides a significant amount of information about the consequences of condensation and even about the history of the mold and the condensation on this roof deck.

We note the following:

  1. There is frost on the nail shank and the deck indicating that the temperature of these and the temperature in the attic are below freezing.
  2. The eye-shaped area clear of dark colored mold around the nail shank indicates that the zinc from the galvanizing on the nail has been absorbed into the plywood around the nail preventing biological growth in that area.
  3. The clear area on the deck around the nail shank also indicates that the mold growth had not been occurring prior to the driving of the nail.  If it had, there would be remnants of the mold growth in this area.
  4. The light strip along the top of the rafter is evidence of whitening of the wood from cleaning with a bleach mixture.  Previous cleaning with bleach indicates that mold growth, and thus condensation, had occurred previously.
  5. The nail shank is not corroded, but exhibits some oxidation indicating that the nail is somewhat new.  The age of the nail may be better assessed by comparison with other exposed nail shanks in the attic.