I am planning to build a new accessory dwelling unit (granny flat) in my backyard. I really like this design from https://node.eco/
However how do I manage the flat roof water run off? Is it just very low pitch or something?
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Slope the surface of the roof to one corner - the black surround hides it.
The slope does not need to be much (0.5cm per metre or 1/4" per 3 feet roughly - my guess) but the roof should not have dips in it ie you should not get puddles after rain.
Then organise the downpipe as required.