The variability of test results when assessing the resistance of windows to water and air penetration using BS4315.

Reports a programme of tests of the resistance of windows to air and water penetration. These were intended to assess the variation in the results due to different designs of window, differences between individual windows of the same type, different pressure test boxes, and different test operators. Gives tables of results and finds considerable variation but no single source of the variation. Suggests new test procedure and a statistical criterion for acceptance.