Beneath the streets of Seoul are hidden semi-basement flats known as banjiha. But these homes can be deadly

As you take your first step into Jung Won-young's home in Seoul, the floor sinks.

Sticky tape has been plastered over the laminate in an attempt to hold it together, weeks after record flooding left it bubbled and cracked. 

Further inside the 71-year-old's underground flat, the water damage is much worse.