The eave is the lower, horizontal edge of a sloped roof — the part that hangs past the wall. The projecting section is the overhang, formed by the rafter or truss tails beyond the birdsmouth. It is finished with a fascia board on the face and a soffit underneath. Eaves throw rainwater away from the siding and foundation and shade windows in summer. Typical US overhangs run 12”–24” measured horizontally; in a rafter calculation, that level overhang is multiplied by the pitch’s slope factor to get the extra rafter length.
The eave is also where the attic breathes in. Vented soffits supply intake air that flows up under the roof deck and out the ridge or roof vents. The IRC (R806.2) requires net free vent area of at least 1/150 of the vented attic floor area, or 1/300 when the code’s conditions are met (such as balanced high and low vents).
At the roof edge, the IRC requires a drip edge along eaves and rakes under asphalt shingles (R905.2.8.5). In areas where ice dams are a known problem, an ice barrier membrane must run from the eave edge to a point at least 24” inside the exterior wall line (R905.1.2), so meltwater backing up behind ice can’t leak into the wall.