dpc Hello from Surrey! Need help with External wall now an internal wall.

[Rusty_Nutz]

Hi Build Hub,

Carrying out a rear extension on our detached 1960's house in Surrey.
In need of a bit of advice or guidance regarding the possible need for damp proofing to an existing external wall that now becomes an internal wall after an extension. I plan to keep it as exposed brickwork as attached visual.

 

The problem (or maybe it's not a problem) I have is the new extension lower floor level (blue line) is a lot lower then the existing DPC (pink line).

 

Is there a chance moisture will run up that external wall and create damp issues? If so, what would be my best course of action? Do I treat it like a basement and tank the wall?
 

Hoping that all made sense.

Many thanks in advance.
 

Edited April 29, 2023 by Rusty_Nutz