We recently had our roof done.  There was much damage from rot due to insufficient ventilation in the rafters.  This is a cathedral ceiling, 2 x 8 rafters.  Many rafters were replaced during the job so we removed all the drywall and insulation.  A ridge vent and smart vents were installed in the roof to provide proper ventilation in the future.  Now that the roof is complete, we are considering using pine ship lap such as pine V-rustic on the ceiling instead of drywall.  My concern is that the pine will allow some airflow through the joints that don’t fit snugly, especially during the winter when they shrink a bit.  This could create airflow from inside to outside through the new roof vents.  Would drywall be a better choice?  We don’t have extreme temperature changes here in the San Francisco Bay Area.  Anyone have experience with this?