To modify the requirement in Sentence 2.4.10.6.(1), that would otherwise permit a higher load, where nominally horizontal offsets in soil-or-waste stacks are 1.5 m or more in length and resistance to flow is higher.
This is to limit the probability that hydraulic load drained to inappropriately sized soil-or-waste stacks will lead to a drainage system backup, which could lead to unsanitary conditions, which could lead to harm to persons.