Tim Hance with All Islands Home Inspections recently discovered deterioration and fungal growth at OSB roof sheathing immediately behind gutters at a recent Oak Harbor, WA home inspection. It is important to keep gutters clear and free of debris to help prevent spillage that can lead to sheathing deterioration. Also, although not per se required, I always recommend installing a metal drip-edge flashing detail at all eaves (e.g., behind gutters) that is run underneath the roof coverings and over the fascia trim to further prevent water damage in the event that gutters overflow or water is introduced.