The repeatability and reproduceability of test results on windows and wall span elements and the expected results.

Discusses variations in the test results which occur with the laboratory procedures for assessing the air and water penetration attributes of windows. Presents data for windows examined under British Standard BS 4315 : part 1 "Methods of test for resistance to air and water penetration - windows and gasket glazing systems". Considers the implications of thesetests for the development of performance levels for use in standards and procurement documents, and proposes a two-stage statistical procedure, based in the first instance on tests on five windows. The use of such a procedure will permit the acceptance with confidence of a window type under the assessment procedure. Emphasises the need to correlate laboratory assessment of windows with the actual performance of windows installed and in use in buildings.