[MisterTea]

As someone who has owned two commercial flat roof buildings I cant stress enough that you MUST do inspections of your roof at least twice a year. Especially if you live in a big city. I've had backups caused by kids roofing balls and bottles, stolen purse, dead squirrel, dirty balled up diapers from the neighboring apartment building. City living for ya.

[numbsafari]

Yeah, I'm pretty sure in this case it was a combination of having a 4ft parapet around the entire roof, and having basically never done an inspection. Not enough drains and they were all full of leaf matter.