What Can We Tell from These Photos? (Case Study 20)

Posted by in Attic Ventilation, Case Studies, Shrinkage, Water Sources, Wood | January 04, 2021

When evaluating moisture damage in an attic there may be conditions that appear to contradict each other, such as, those seen in the featured photograph and Figure 1.  However, a closer and more thoughtful examination indicates that the different appearances actually shed light on the history of the moisture damage. 

For example, the featured photograph shows that:

  1. The relatively clean condition of the fracture surfaces indicates that the nails were driven after the underside of the roof deck had become darkened.
  1. The corrosion on the nail shanks indicates that there has been excessive airborne moisture in the attic since the nails were driven through the roof deck. 
  1. The orange coloring of the corrosion indicates that corrosion has been progressing recently.
  1. The multiple lines of checking from shrinkage indicates that the underside of the roof deck has been repeatedly exposed to excessive heat that has dried out the wood.  This commonly occurs as a result of poor attic ventilation.   
Figure 1 Light green and dark biological growth and corroded nail shanks on underside of roof deck.

And , Figure 1 shows that:

  1. The biological growth on the fracture surfaces indicates that the biological growth on the underside of the roof deck has progressed since the nails were driven.
  1. The corrosion on the nail shanks indicates that there has been excessive airborne moisture in the attic since the nails were driven through the roof deck. 
  1. The orange coloring of the corrosion indicates that corrosion has been progressing recently.
  1. The light green coloring of the biological growth indicates that it has been progressing recently.
  1. The darker coloring of the biological growth indicates that it had initiated at a previous time.
  1. The multiple lines of checking from shrinkage indicates that the underside of the roof deck has been repeatedly exposed to excessive heat that has dried out the wood.

And so, from these photographs, which were both take in the same attic, we know that there has been an on-going issue with exposure to excessive moisture and excessive heat.  These exposures began before the roof was re-shingled, but has continued afterward and even more recently.  Furthermore, poor attic ventilation has caused and/or contributed to the excessive moisture causing the darkening and biological growth.

If you can deduce further information, please send me an email and I will update this post with appropriate crediting.

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