Thank you datarebal.
The whole roof/dormers/velux are new. Velux have said the warranty is void because in their view the window has not been installed as per their instructions.
What is CDR?
Picked up this thread as I think I have a similar issue. See photo attached.
The exposed flashing at the bottom of the Velux on the left chatters in the wind.
What do you chaps think is the cause?
