How to Use a King Post Truss

Making a king truss

• 1

  Lay the four pieces that will be used to construct the truss on the ground. The truss is made from two diagonal members that meet at the apex, or top point of the truss. One horizontal beam stretches between the bottom ends of the diagonal, load-bearing members. The king post connects between the apex to the center point of the lower horizontal beam.

• 2

  Fasten these four pieces together with truss plates for wood trusses for a home's roof. Weld the members together for trusses made from metal beams for bridges. Metal trusses should also have a truss plate, or flat piece of steel at each of the joints to distribute the forces on the welds.

• 3

  Construct enough trusses to complete the project. For a bridge, two trusses will support a roadway between them. For a home, where king trusses create the roof system, trusses should be 24 inches apart, across the length of the structure.

Installing a Bridge Truss

• 4

  For a bridge, set the trusses between the concrete piers which form the foundation on each side of the span. A concrete foundation should be poured into the earth to support the weight of the bridge. The trusses are only anchored to the piers on one end of the span. On the other end, the truss rests on a sliding metal surface to allow for expansion and contraction of the bridge from temperature changes.

• 5

  Measure and cut the purlins which will extend between the lowermost beam on the trusses. Purlins run from one truss to the other, and form the foundation on which a roadway can be built. For bridges, the purlins are typically made from the same material as the trusses.

• 6

  Weld the purlins between the trusses, permanently joining the trusses together.

Installing Roof Trusses

• 7

  Lift the trusses onto the walls. The trusses are typically placed 24 inches apart. Lay out the trusses, beginning at one end of the building, and place the trusses next to each other across the entire length of the home.

• 8

  Fasten the trusses together along their diagonal members so that they are perpendicular to the wall, and vertically plumb. Nail the truss beam to the wall plate so that the truss is physically connected to the wall.

• 9

  Apply the roof decking, beginning at one corner of the roof, and laying the sheets on top of the roof trusses. Use the perfectly square 4-by-8 sheets of OSB roof deck material to pull the trusses into shape, square and plumb with one another.