When you sell external doorsets or windows, customers might ask for them to meet the BS 6375-1 standard. But what does that actually involve? In this blog BWF Technical Director Kevin Underwood explains what the standard means and the tests that products must pass to comply.
BS 6375-1 is titled, “Performance of windows and doors – Classification for weathertightness and guidance on selection and specification.” The scope of the standard states that it specifies the exposure categories related to test pressure levels for air permeability, watertightness and wind resistance for external windows and doorsets. It is applicable to all types of vertical windows and doorsets and includes windows in which the opening lights are not fully framed, e.g. adjustable glass louvres.
The standard refers to other standards for test methods and classifications for the three characteristics. These are given in the table below.
| Performance Characteristic | Test Standard | Classification Standard |
| Air permeability | BS EN 1026 | BS EN 12207 |
| Watertightness | BS EN 1027 | BS EN 12208 |
| Resistance to wind load | BS EN 12211 | BS EN 12211 |
The characteristics covered by BS 6375-1 are also essential characteristics defined in Annex ZA of the designated standard BS EN 14351-1 and so the results of the tests given in the table must also be declared on a declaration of performance (DoP). Under the Construction Products Regulations (CPR) almost every external window and doorset will require a DoP.
BS 6375-1 enables the level of performance or classification required for each characteristic to be determined for external windows and doorsets installed into walls up to 15m in height. This is done by working out the exposure category appropriate for the location and type of building into which the windows or doorset is to be installed.
A chart covering the UK gives a basic wind speed for a location. The basic wind speed is used to determine a wind load at sea level which is then factored by the building’s height above sea level, its proximity to the coast or its location in a built-up area, whether the building is on severely sloping ground, near the top of a hill, or near a cliff or escarpment and whether wind can be funnelled by other buildings nearby or whether a window is in a dormer on a roof. For example, a window in a dormer on an isolated building high on a cliff in Scotland will experience high wind pressure while a bungalow located in the centre of Oxford will experience a much lower wind pressure.
All three tests can be undertaken on the same sample at a test laboratory with an appropriate test rig.
Air permeability: The sample is first subjected to increasing steps of positive air pressure with the volume of air leaking through the sample measured at each step. The sample is then subjected to increasing steps of negative air pressure and the air leaking through the sample is measured again at each step. The results are reported in terms of m3/h per metre length of the opening joints and per m2 of the window or door area at both the positive and negative pressures and the average value at each pressure. For classification the average figures must not exceed the maximum permitted values for a class.
Water Tightness: Any trickle vents in the window or doorset can be taped over. The test specimen is mounted in the test rig with the external side facing a row of nozzles located near the head and angled down at 24°. The window or doorset is first subjected to a 15 minute spray at zero pressure and then the pressure is increased in steps until there is continuous or repeated wetting of the inside face or parts of the specimen that are not intended to get wet. The result is given as the maximum pressure that was maintained before water penetration occurred.
Wind load: This test is undertaken in three stages. The specimen is first subjected to both positive and negative pressure equal to the desired in-service wind load and any deflection of the components is measured. The deflection should be less than l/150 where “l” is the length of the component. A repeated positive and negative pressure equal to half the in-service pressure is then applied to the specimen in 50 cycles. Any damage to the sample is noted. Finally, a safety test is done by applying both a positive and negative pressure which is twice the in-service pressure after which the window or doorset should remain closed and no parts should have become detached.
BS 6375-1 gives the required classes for each of the three characteristics against the exposure category found for the location of the external window or doorset. As the exposure category increases, this will be as the in-service wind load increases, the air permeability must not increase, the product must not be damaged, it should not leak water and it should limit the uncontrolled air infiltration or drafts.
