To limit the probability of insufficient vertical clearance, which could lead to the blockage of exhaust openings by vegetation, earth or debris, which could lead to inadequate exhaust airflow, which could lead to excessive positive pressure in dwelling units, which could lead to:
This is to limit the probability of the generation of pollutants from biological growth or from materials that become unstable on wetting, which could lead to negative effects on the air quality of indoor spaces, which could lead to harm to persons.