BCT 122 Roof Framing 1

Roof Framing ProcedureSequence

Wall Plate Check & Layout• Verify (measure) building span dimensions.• Check walls for straight and bracing.• Lay out plates for rafter and Joist O/C spacing.

Ceiling Joist• Ceiling joist parallel to rafters that make the entire

span may fall to either side of the rafter and are nailed securely to the wall plate (3 – 8d) and laterally into the rafter. (3 – 10d)

• If the ceiling joist does not span, it must be lapped a minimum 3” and nailed together.

• Ceiling joist starting on opposite sides of the rafter require a block under the rafter to tie the rafters on the interior partition.

• Joists may need to be clipped if they extend above the rafter. Remember Crown up!

Joist Blocks

Clip Joist Ends if Necessary

Calculating the Common Rafter• Using the Pythagorean theorem, calculate the

hypotenuse of 12” unit run & the given rise. This is the unit line length.

• Line length factor is the unit LL ÷ 12”.• The rise factor is the unit rise ÷ 12”.• The rafter length is unit LL x ½ the span.• The rafter tail length is overhang inches x LL factor.• The rafter shortened for a ridge board is ½ the ridge

thickness x the LL factor or ½ the ridge thickness perpendicular to the plumb cut.