How to Add a Roof Truss

You can install prefabricated trusses that come with instructions for installation. A less expensive option, but one requiring carpentry skills, is to build the trusses yourself. How many trusses you need and in what size and configuration depends on the size of the roof and whether it is gabled, hipped or flat. Pitched, gabled roofs have triangular-shaped trusses. Trusses of hipped roofs are variants of the basic triangular shape that gives strength from loads pressing downward.

Chalk line
Tape measure
Power saw
2-by-4s or 2-by-8s
3 galvanized steel reinforcing gussets for each truss
Power screwdriver
1 ½-inch screws
3-inch screws
Hammer
10d nails
Crane
Carpenter’s level
4-by-8 foot plywood or oriented strand board (OSB) roofing panels
18- or 20-gauge H-clips
6d galvanized nails

Instructions

- 1
  
  Working with 2-by-4s.
  
  Order enough 2-by-4s to build trusses spaced 24 inches apart. Buy enough plywood or OSB panels to cover the trusses plus 2-by-4s for temporary support. The panels forming the roof deck make the trusses rigid and are necessary to complete the installation.
- 2
  
  Basic triangular roof trusses on a house.
  
  Buy gussets, screws and nails. The sloping sides of the triangle that support a basic gabled roof deck are called the upper cords. The horizontal bottom is the lower cord. Buy gussets to install where upper cords meet at the top of the triangle and gussets for the bottom corners. Buy screws to secure the gussets and nails to secure the trusses to the top of the wall.
- 3
  
  Installing roof trusses.
  
  Measure and cut 2-by-4s for the lower and upper cords. Cut two diagonal support braces from 2-by-4s. These will run one-third of the way from opposite ends of the lower cord to the middle of the upper cords. Cut two braces from 2-by-4s to run from the same points on the lower cord to the top of the truss.
- 4
  
  Working on triangular roof trusses.
  
  Measure and cut 2-by-4s for temporary lateral braces on top of the installed trusses and temporary braces that run from the ground to the end trusses. You will remove these braces when you add the deck panels.
- 5
  
  Roof trusses showing interior braces.
  
  Secure the gussets with 1 ½-inch screws. You will now have a basic triangle. Nail the interior supporting braces into place with 10d nails. If you want a stronger roof, use gussets and screws to secure the interior braces.
- 6
  
  Interior braces of roof trusses.
  
  Beginning at one end of the wall, mark installation points every 24 inches. You will secure the ends of the trusses OC, meaning on the center of these marks.
- 7
  
  House exterior showing triangular roof trusses.
  
  Lift the trusses into place. Secure the ends onto the installation points on the wall with 10d nails. Make sure the trusses are plumb.
- 8
  
  Trusses of hipped roofs are more complicated.
  
  Nail 2-by-4s laterally across the trusses. This will keep the trusses rigid and plumb until you add the deck. Add additional 2-by-4 supports from the ground to the end trusses.
- 9
  
  Triangular trusses with interior supports.
  
  Removing the temporary support 2-by-4s as you work, nail the plywood or OSB panels to the cords with 6d nails. For a stronger, more rigid roof, add metal H-clips between the trusses where the ends of the panels meet.

Does BOMA Adjust for Sloped Walls?

How to Truss a Flat Roof

Home Building