Before Installing Ridge Vent
This looks like someone has removed the roof
ridge vent and is going to replace it or do some repair work.
I have never been able to install a continuous ridge vent in the areas where I work, because you need the roof ridge for some of your structural nailing.
The roof ridge is part of the diaphragm nailing and helps hold the house together in case there is an earthquake.
I worked on a job one time where the building inspector told us that the roof would need a continuous ridge vent, and the structural engineer told us we were not allowed to damage the diaphragm nailing. At all...
The structural engineer of coarse takes precedence over any building inspector and in a case like mine he was the winner. No ridge vents were installed on that job, however the city did require more dormer vents that I have ever seen on one house before.
The city normally wins in the long run.