Green or dark patches of algae and moss usually show up where water tends to sit longer than it should. Maybe the slope is wrong, maybe a drain is partially blocked, or maybe certain areas are always damp.
While a little bit isn’t instant disaster, persistent growth is a sign that those areas don’t dry properly. Over time, constant dampness weakens surfaces, eats into coatings, and can lead to leaks in the spaces below.
If you see a lot of mossy, slimy areas, you know there’s a drainage or slope issue that someone needs to take seriously—either now or soon.
