What’s Under That Dip in the Roof?

Posted by in Case Studies, Wood | January 18, 2021

The roof surface looked level everywhere except that one dip near the ridge (featured photograph).

What would case the dip in the roof surface?

From the attic, I was able to see that a small area of the roof deck had fractured (Figure 1).

Figure 1 Roof deck boards fractured under dip in roof surface.
Note large knot in farther board.

The puncture pattern of the fracture in the two deck boards indicates that the fracture was caused during an application of a concentrated load.  Further examination of the boards disclosed that one of the boards had been originally weakened by a large knot and that both boards became weakened further by lose of moisture from exposure to excessive heat and decay from exposure to excessive airborne moisture.  Both the exposures to excessive heat and to excessive airborne moisture in an attic are commonly due to inadequate attic ventilation.  And that was the cause in this case. 

The weakened boards became fractured under the weight of foot traffic.