Tim S coughed up some electrons that declared:

Think I'll give them a ring and see why they've stated that. They might
have meant a public walkway rather than a garden path - it's not at all
clear on their diagram.


I did and they said, for what it's worth, that the diagram is referring to a
flue discharging onto public walkway at less than 2.1m in height.

Makes perfect sense.

Cheers

Tim