Acceptable Solution E2/AS1 requires stop-ends to cavity window head flashings (their job is to prevent water that gets onto the head flashing from draining into the window cavity) and a minimum cross-fall of 15°. Flashing upstands need to be increased by 25 mm in the extra high wind zone, and a seal is required between the head flashing and the window flange in very high and extra high wind zones

Designers should ensure that these details are specified, and builders should ensure they are properly installed.

Updated: 9 September 2014