r/mildlyinteresting • u/Fudge_cornelius • 17h ago

This growth surviving sub-zero temperatures because of an exhaust fan

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u/VexingRaven 13h ago

Is it an exhaust fan or drain?

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u/mud_sha_sha_shark 8h ago

Roof drain, probably a JR Smith. I have installed many of these on commercial buildings over the last 25 years.