When do doors and windows become walls?

The NHBC wanted to address arrangements where facades, or parts of facades, have been formed by a combination of windows, both horizontally and vertically, in many cases being more than one storey in height.  The intention was to try and distinguish between what could be described as a small combination of windows and a more extensive array of windows creating a significant part of the building façade with a higher technical risk.

There are two Chapters in the NHBC Standards – 6.7 ‘Doors, windows and glazing’ and 6.9 ‘Curtain walling and cladding’ and it was thought to be important that both scenarios provided a property covered by NHBC with a durable system which would be stable, weatherproof and have appropriate in-service performance.  This has now been agreed by the NHBC Standards Committee and will become effective from January 2013.

The new definition by NHBC:

The Task Group agreed that:
1. Coupled door and window assemblies (including spandrel panels) that span one storey or more,
or are not contained between a structural floor and ceiling, are very similar in their function to curtain walling and, therefore, the guidance set out in Chapter 6.9 ‘Curtain walling and cladding’ should be used as a benchmark for acceptance.

2. Coupled door and window assemblies (including spandrel panels) that are contained between a
structural floor and ceiling within a single storey can be considered in accordance with Chapter 6.7
‘Doors, windows and glazing’.

This information is included within NHBC Technical Extra Issue 0.6

NHBC have also stated that hose testing will be adopted in future.  It may not be a perfect solution but it does provide some assurance that what has been assessed does perform on site. It also sends a clear message to installers that they need to get it right as it will be tested.

Currently, there is a standard ‘BS EN 13051:2001 Curtain walling. Watertightness. Site test’ which covers curtain walling only. Windows are covered by ‘BS 6375-1:2009 Performance of windows and doors. Classification for weathertightness and guidance on selection and specification’ and ‘BS EN 1027:2000 Windows and doors. Watertightness. Test method’. This method for windows is a laboratory test only.

This could mean that any stacked window or door system that spans more than one floor may have to come with a Centre for Windows and Cladding Technology (CWCT) certificate from testing to TN41. Site testing for Watertightness.

I am keen to canvass opinion from BWF members on this issue. If you have a view on this article please contact the BWF Technical Team.