Cut parallel lines
Connect the two cuts
Raise the vent up to the soffit
Attach the vent to the soffit
Remove any insulation from the new vent
Install the ventilation baffle
Finally, to ensure that the airway to the vent remains open, staple a ventilation baffle to the plywood sheathing in each rafter bay. The molded polystyrene baffles, available at home centers and lumberyards for about $1 each, form channels that hold insulation at bay and direct incoming air upward.