lookout
A joist that extends in cantilever out from the exterior wall (or wall plate) of a building, supporting the roof sheathing and providing a nailing surface for the fascia boards.
lookout: a cantilever joist that holds up the roof overhang
A lookout is a framing member that projects horizontally beyond the exterior wall plate, carrying the weight of the roof edge and the materials attached to it. It functions as a cantilevered beam, anchored into the wall frame while its free end supports the outer courses of roof sheathing, the fascia board, and sometimes guttering. The member is typically a 2x6 or 2x8 dimensional lumber joist, though the span and load determine the required depth and spacing.
Lookouts work in pairs or groups spaced 16 or 24 inches on center, running perpendicular to the wall. They are nailed or bolted into the top plate and the rim joist of the upper floor frame, relying on this connection to resist the overturning moment created by the cantilevered load. The extension beyond the wall usually runs 12 to 24 inches, depending on the desired overhang depth and local wind and snow loads. At the free end, lookouts create the surface to which fascia boards and soffit framing are attached.
Common failure modes include inadequate connection strength at the wall, which can cause the overhang to sag or separate, particularly in areas with heavy snow or high winds. Undersized lookouts that deflect excessively will crack the fascia and compromise the seal of the roofing. Rot develops quickly if lookouts are exposed to moisture without proper flashing or end sealing, especially at the rim joist where water can wick into the endgrain.
The term lookout likely derives from the visual character of the detail: the joist projects and appears to look out beyond the wall line. In some regions and trades, the same component may be called a tail rafter, outlooker, or roof bracket, though these terms can carry slightly different meanings depending on the roof geometry and construction method.
Lookouts are standard in residential stick framing and light commercial construction. They are essential for creating the overhangs that protect walls and foundations from weather and provide useful roof lines. In modern energy-conscious framing, careful detail is needed to avoid creating thermal bridges through the insulation at the overhang, often solved by blocking or raising the insulation level at that line.