Inadequate Roof Flashing
We are often contacted to evaluate the source of moisture or water that is causing apparent mold growth, decay, moisture staining, or another type of water damage. Sometimes the cause of the moisture or water source is a little easier to find than others.
In this week’s case study one of the sources was obviously from roof leakage rather than condensation, or a plumbing leak. When we examined the roof above the interior moisture and/or water damages, the cause of the roof leakage was obvious.
The first issue was the lack of a drip edge for a short length rake (Figure RL-1). The lack of a drip edge allowed roof runoff to decant under the shingles and the metal valley and behind the fascia trim piece. A well-thought out detail with a drip edge and a flexible membrane flashing under the metals may have provided a better the solution. The joint between the brick and the metal and shingles and re-routing of the downspout discharge also needed to be considered in the flashing detail (Figure RL-2).
We also observed a separation in the trim and flashing that would allow infiltration of roof runoff. The separation was under a downspout discharge where the accumulation of tree debris would direct runoff behind the siding (Figure RL-3).
At another location we found that the step flashing for the wall terminated into the back of the brick (Figure RL-4). This detail directs roof runoff into the wall. The roofing cement at this location indicates that there had been a previous attempt to stop previously observed leakage (Figure RL-4).
As the old maxim says, “The devil is in the details.” And certainly, the details on this roof diminished the water shedding ability of the roof covering.