To limit the probability that the airtightness of the enclosure will lead to siphonic action or back pressure in drainage systems, which could lead to trap seal failure, which could lead to the entry of sewer gases into occupied space, which could lead to negative effects on indoor air quality, which could lead to harm to persons.
To limit the probability that an inability to access air admittance valves for inspection and maintenance purposes will lead to trap seal failure, which could lead to the entry of sewer gases into occupied space, which could lead to negative effects on indoor air quality, which could lead to harm to persons.