Step 3: How To Build Perfect Barn Style Gambrel Roof Trusses

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Build the trusses now because the empty floor will be part of your temporary truss jig.

Plus the floor makes a nice clean work space to cut and organize the pieces on.

Calculate number of pieces to cut

See table 3 for the truss count. Take the number under the column of the center spacing (16 O.C. Or 24 O.C.) you want to use.

That truss count number less 1 times 6 ( count-1×6=total ) is the number of OSB web pieces you’ll need to cut.

Take the same truss count number times 4 for the number of 2×4 truss pieces you’ll need to cut.

Cut OSB web pieces

Rip some OSB into strips 12in wide and 8ft long. Cut these strips into pieces 6in long. You’ll need enough of these 6×12 pieces to build the number of OSB web pieces you calculated above. Leave them square at this time.

Cut truss pieces

barn style gambrel roof trusses

See table 2 to get dimensions “G” and “H”.

All the truss pieces are identical. Cut the necessary number of truss pieces with 22 1/2 degree angles on each end and a length of “H” along the long side.

Temporary truss jig

temporary truss jigBuild a temporary truss jig by screwing 2 long 2×4’s to adjacent edges of the floor at 90 degrees to each other.

Align them to the edges of the floor and attach with 3 to 4 screws along their length. This way the floor acts as a giant builders square.

Cut 3 stops

Cut 3 OSB pieces about 1 1/2in x 3in to use as stops.

Attach stops

temporary truss jig layout
From the inside corner of the jig measure up a distance of 1/2 “G” and place a mark on the inside face of the 2×4. Attach the first stop here with two 2in drywall screws.

Attach the second stop the same 1/2 “G” distance along the bottom of the jig.

Attach the third stop at distance “G” from the inside corner.

Mark and cut OSB web pieces

half g stopsPlace 2 truss pieces between the 1/2 “G” stops. Put the ends firmly into the stops and bring the top ends together.

Place a 6×12 piece of OSB under the joint where the ends meet. Make sure it’s symmetrical.

Mark along the top of both truss pieces with a pencil then remove the OSB piece.

Cut along these lines and use this piece as a template to mark and cut the rest of the OSB web pieces.

Assemble half trusses

Build all the half truss assemblies by placing truss pieces in the jig and attaching the OSB web with 6 to 8 (1 3/4in) nails or screws into each side. You can use glue or construction adhesive for extra strength.

Do this to the first side only this point.

Before you remove the first truss place a pencil mark on the floor at the outside edge of the joint. If all further trusses match up to this mark then you know the trusses will the same. If they don’t line up then you might have a problem and need to redo something.

Combine half trusses

build full trussesPlace 2 half trusses between the “G” stop and the inside corner and bring the ends together.

Attach an OSB web piece at the joint.

Mark the outside of this joint on the floor to use as a check for the rest of the trusses.

Attach OSB web pieces on other side

Gently lift this truss at the center joint and pull it across the floor slightly beyond the upper 1/2 “G” stop. Raise the truss up on its ends and flip it over to the other side. Place an OSB spacer under each end then attach an OSB web piece to each of the 3 joints.

Except the last 2 trusses

Do this for all except the last 2 trusses. Leave the OSB webbing off the back side of the last 2 because these will be the gambrel end trusses that you will nail the siding to.

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