How to Build Roof Eaves From Roof Trusses

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Eaves are formed by the overhang of roof rafters beyond the wall of a house. Most roofs today are framed with trusses, which are rafters with horizontal bottom boards called chords and internal vertical or diagonal braces. Trusses form eaves two ways, depending on the bearing point, or the spot at which the truss sits on the top of the wall. Trusses with bearing points on the bottom chord have rafters that overhang the wall to form the eave. Trusses with bearing points on the ends of the rafters form eaves by extending past the wall.

Things You'll Need

  • Truss design manual
  • Prefabricated roof trusses
  • 2-by-4-inch rafter boards
  • Soffit sheathing
  • Select a roof style and a type of truss, which will depend on the pitch or slope of the roof, its width and the amount of interior space needed in an attic under the roof. Determine the bearing point of that truss style and the amount of overhang needed to drain water away from the wall. Low or medium pitch roofs usually have at least 18 inches of overhang for an 18-inch eave; steeper pitches may have less overhang because they drain water faster.

  • Leave eaves open, or close them with soffits. Open eaves leave rafter ends or tails exposed. Closed eaves have a soffit, a covering on the bottom of the overhang.

  • Make soffits by installing "lookout" rafters, 2-by-4-inch boards between the wall and the ends of the truss rafter ends. Nail lookouts to the wall tops and the ends of the rafters. Cover the bottom of the eave with plywood or oriented strand board (OSB) sheathing, nailed to the lookouts. Add a facing board, or fascia, nailed on the ends of the truss rafters to enclose the eaves

  • Block open eaves with boards between truss ends from the bottom of the roof sheathing to the top plate of the wall. Nail a board between each pair of trusses to seal the attic area from wind and animals. Each board needs to be the depth of the truss end and the width between truss ends. Some building codes require eaves blocking on exposed truss ends, but the practice is less common now because many fire codes and architectural styles have demanded closed eaves.

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