(1)
Except as provided in Sentences (3) and (4), traps shall be protected by a vent pipe.
(2)
Drainage systems may require additional protection as provided in Subsections 7.5.4. and 7.5.5. by the installation of
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(i)
(j)
(k)
(l)
(m)
dual vents, or
(n)
(3)
A trap that serves a floor drain or hub drain need not be protected by a vent pipe separately where
(a)
the nominal pipe size of the trap is not less than NPS 3,
(b)
the length of the fixture drain is not less than 450 mm,
(c)
the fall on the fixture drain does not exceed its nominal pipe size.
(4)
A trap need not be protected by a vent pipe
(a)
where it serves
(i)
a subsoil drainage pipe, or
(ii)
a storm drainage system, or
(b)
where it forms part of an indirect drainage system. (See also Clause 7.4.2.3.(2)(b))