Damp into new wall

[5teves]

Hi

I built a cavity wall fpr a new extention at the back of my house.
This new wall is built perpendicular off the exisiting back of the house which is also a cavity wall.

I'm noticing lots of damp on the new wall internally when it rains outside and can only assume that the damp barrier failed because the exisiting old wall crosses the cavity of the new wall on both leafs...

Any suggestion to fix this problem?

 

[catlad]

Difficult after the event! You are supposed to cut a 50mm slot in the brickwork.

 

[Mr Chibs]

Difficult after the event! You are supposed to cut a 50mm slot in the brickwork.

Do you mean a kind of cavity? Top to bottom.

I ask, as I’ll soon be helping out on an extension

 

[catlad]

If you are going to turn an external wall into an internal wall then you run the risk of damp if you don't cut into the brickwork to create a cavity.