Weather Testing of Windows

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There are performance standards for the basic weather and mechanical performance of all types of window whatever the frame material used for the product. The standard in the UK is BS 6375 and this is divided into Part 1 for basic weather resistance and Part 2 for operation and strength characteristics.

Weather Performance (BS 6375: Part 1)

BS 6375: Part1: "Performance of windows: Classification for weathertightness" is the basis for assessing the weathertightness of windows up to a maximum frame size of 3 metres and provides a means of selecting a performance level against which the window may be assessed. This standard also includes guidance on the selection and specification of windows.

The test methods called up by BS 6375 to measure weather performance are the various parts of BS 5368. This standard can be applied to windows manufactured from any material.

BS 6375 calls up test methods for three basic parameters of window performance. These are:

These tests are then related to the location, both geographically in the UK and physically in the building to provide an assessment of the required performance of the window.

Air permeability - BS 5368: Part 1: 1976 (or European Standard EN 42)

This defines the ability of the window to resist air penetration when it is subjected to differential pressure and is a measure of the air which seeps through the test window at given test pressures.

The average amount of air which leaks through a metre of the opening weather seal (as seen from the inside of the window) is measured and the measurements are calibrated in cubic metres (m3), per hour, per metre of opening seal. i.e.m3/h/m of opening seal.

The test starts with three pre-pulses of air to a pressure higher than the maximum to be applied in the test. At the end of this, the window is opened and closed to check correct operation and fastened closed. The window is subjected to increasing positive pressure in stages for periods of at least 10s up to the maximum pressure required for the test. The pressure is then lowered in the same stages. The air permeability rate is measured at each stage and the highest rate for the relevant pressure stage (whether increasing or decreasing) is recorded. This graph of the results is compared with the graphs of Figure 1 of BS 6375 to give an air permeability rating in Pa.

Watertightness under static pressure - BS 5368: Part 2: 1980 (EN 86)

This defines the ability of the window to resist water leakage into parts of the building not designed to be wetted.

The test starts with three pre-pulses of air to a pressure higher than that to be achieved for the test. At the end of this, the window is opened and closed to check correct operation and fastened closed. Water is sprayed on to the window for set periods of time and the pressure in the test rig is increased in steps until failure occurs. Failure is defined as leakage of water to what would be the inside face of the window if installed. The pressure and location of first leakage are recorded. Watertightness is expressed as the maximum test pressure at which the test window remained watertight. For example: Class 300 (Pa) denotes that the window remained watertight at 300 Pa, only leaking above this pressure.

Wind resistance - BS 5368: Part 3: 1978 (EN 77)

This defines the ability of the window to resist positive and negative pressure and to check that the window has a permissible deformation, maintains its characteristics and does not endanger users.

The test starts with three pre-pulses of air to a pressure higher than that to be achieved for the test. At the end of this, the window is opened and closed to check correct operation and fastened closed. The window has internal pressure applied and the deflection of the window is measured at various points. The pressure is then reduced to zero and the residual deformation measured. For assessment of the response to repeated deformation the window is cycled through rapid pressure pulses at the declared design wind pressure and the operation of the window checked afterwards.

A final high pressure safety test is carried out and any damage, functional defects or deformation noted. Wind resistance is expressed as the exposure category or design wind pressure at which the test window met the deflection and permissible damage limitation set out by BS 6375: Part 1: 1989. Wind resistance pressure Class 1200 (Pa) denotes the test window met the deflection, and damage limitations at a test pressure of 1200 Pa in the form of wind pressure and of wind suction (wind rushing past, or eddying up the face of a building can cause the window to be drawn outwards).

 

Test pressure cycles for BS 5368 Parts 1 to 3

 

The introduction of the relevant EN standards means that the test cycles for the testing of all windows is now the same throughout Europe. The window is stabilised with the three pre-pulses and then tested with the subsequent pulses.

Mechanical Performance (BS 6375: Part 2)

The specification for the operation and strength characteristics is BS 6375: Part 2 and this covers areas such as opening cycles and other mechanical tests.

Last edited: 20/04/12 

Tangram Technology Ltd. 1998

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