Understanding BS 6375-1: What window & doorset sellers need to know

When you sell external doorsets or windows, customers may ask whether they meet BS 6375-1, but what does that actually involve? Here, BWF Technical Director Kevin Underwood explains what the standard covers and the tests required for compliance.

BS 6375-1, Performance of windows and doors – Classification for weathertightness and guidance on selection and specification, defines the exposure categories and associated test pressure levels for air permeability, watertightness and wind resistance of external windows and doorsets. The standard applies to all types of vertical windows and doorsets, including windows where the opening lights are not fully framed, such as adjustable glass louvres.

The standard references additional standards for the test methods and classifications for each of the three performance characteristics, which are given in the table below. 

Because these characteristics are also essential characteristics defined in Annex ZA of the designated standard BS EN 14351-1, the test results listed 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 requires a DoP.

BS 6375-1 allows specifiers and manufacturers to determine the appropriate performance level or classification for external windows and doorsets installed in walls up to 15m in height. This is achieved by identifying the exposure category appropriate to the building’s location and type.

A UK-wide chart provides the basic wind speed for any given location. This value is then used to calculate a wind load at sea level, which is adjusted to account for factors such as:

• The building’s height above sea level

• Proximity to the coast or exposure in open country

• Whether the building is located in a built-up area

• Sloping terrain, hillsides, cliffs or escarpments

• The potential for wind to be funnelled by nearby buildings

• Whether a window is in a feature such as a dormer

  
  

For example, a window in a dormer on an isolated building high on a cliff in Scotland will experience far higher wind pressure than a bungalow located in central Oxford. All three performance tests can be carried out on the same sample at a suitably equipped test laboratory.

Air permeability

The sample is subjected to increasing steps of positive air pressure, with the volume of air leaking through the product measured at each step. The test is then repeated with negative air pressure. Results are reported in m³/h per metre of opening joint and per m² of overall area at both positive and negative pressures, along with the average value. To achieve classification, these averages must not exceed the maximum permitted values for the relevant class.

Watertightness

Trickle vents may be taped over for the test. The sample is mounted externally facing a row of angled spray nozzles. Following a 15-minute spray at zero pressure, pressure is increased stepwise until continuous or repeated water penetration occurs on internal surfaces or those components not intended to become wet. The classification is the highest pressure maintained before leakage occurs.

Wind load resistance

This test has three stages:

1. Deflection test – The product is subjected to positive and negative pressures equal to the intended in-service wind load. Any deflection is measured and must be less than L/150, where L is the component length.

2. Repeated pressure cycling – 50 cycles at half the in-service pressure are applied, and any damage recorded.

3. Safety test – Positive and negative pressures twice the in-service load are applied. The product must remain closed, with no components becoming detached.

   
   

BS 6375-1 provides the required classes for all three characteristics based on the exposure category calculated for the installation location. As exposure increases, and therefore in-service wind load increases, products must continue to resist damage, avoid water leakage, limit uncontrolled air infiltration and maintain acceptable air permeability levels.

To find out more, see www.bwf.org.uk.