Short Answer
Fascia is the exterior trim along the roof edge. It often supports or interfaces with the gutter system.
Detailed Explanation
Fascia is the vertical board or trim that runs along the lower edge of the roof — it's the board that gutters are typically attached to. It serves as a finished edge for the roof, protects the roof framing from weather, and provides the attachment surface for gutters. Because gutters are fastened to the fascia, the fascia must be structurally sound to support the weight of gutters full of water, snow, or ice. Fascia can be made from wood (most common, but susceptible to rot), aluminum (durable, low-maintenance), vinyl, or composite materials. Wood fascia that has rotted may not hold gutter fasteners properly, leading to gutter sagging or detachment.
Why It Matters
Fascia is the structural support for gutters. Rotted or damaged fascia compromises gutter attachment and can lead to gutter failure.