Why is my roof leaking?

99% of all leaking windows are down to poor installation. The six common installation faults are:

• C-Channels fitted the wrong way round
• The hood and top apron are not joined correctly (slate extension piece not fitted)
• The frame side flashing is not fitted correctly under the C-Channels
• The rubber end caps have been removed
• The flashings are not overlapped in the correct order
• The window has been fitted in a roof with a pitch less than 15°