6.7.4 Coupled door and window frame assemblies

System design#

Coupled door and window frame assemblies should be supplied as a standard system comprising only of components designed and detailed by the system manufacturer.

Weathertightness #

Jointing details should be designed on the principle of two lines of defence with flexible inner and outer seals. The cavity between the seals should be drained to remove any water that bypasses the outer seals.

Weathertightness of coupling joints may be adversely affected by deflections under windload. Weathertightness of coupling joints should be demonstrated by appropriate laboratory testing of an assembly.

Testing should be undertaken by a UKAS accredited test laboratory. During testing, there should be no leakage onto the internal face of the system at any time.

On completion of the test there should be no standing water in locations intended to remain dry. Any remedial modifications to the system that are made to pass the test should be reported and incorporated into the installed system.

To avoid difficulty in interpreting the results it is good practice to agree which materials and zones within the system may be allowed to get wet.

Alternative jointing details should not be used unless they have been proven by testing. The interface between the assembly and the surrounding building envelope should be a robust detail that is easy to understand at the construction stage. It should be evident how the coupling and interface details are to be constructed and should be easy to inspect and/or test.

Structural integrity#

Coupled door and window frame assemblies should be designed as an engineered system to support their self-weight, resist and safely transfer imposed loads back to the supporting structure.

Windows tested and classified to BS EN 14351-1 are subjected to wind load tests, however, as the perimeter of the window is supported by the test box, the response of the perimeter frame to wind load will not have been fully assessed.

The perimeter frame of the window used in an assembly needs to be able to resist the wind load in bending or the joining component needs to provide support and contribute to the overall stiffness of the system in resisting deflection arising from wind pressure and other loadings including accidental impact.

For window assemblies, it is recommended that the main structural members of the assembly satisfy class B for which the allowable deflection is span/200 under the design wind load in both positive and negative directions. This is the limit which applies for curtain wall mullions in BS EN 13830.

Movement accommodation#

As window assemblies are larger than individual windows, the amount of movement to be accommodated is also likely to greater. Coupling joints and interfaces with the surrounding construction should be designed to accommodate thermal expansion/contraction of the frames and movement of the structure, whilst remaining weathertight.

Thermal bridging#

Coupling joints, brackets, and fixings may create additional heat flow paths resulting in low surface temperatures, increasing the risk of surface condensation.

Coupling joints and interfaces with the supporting structure should be designed to minimise the effects of thermal bridging and risk of condensation including the appropriate use of thermal breaks.

The thermal assessments of linear coupling joints and interfaces with the supporting structure should be checked to assess the risk of surface condensation.

The assessments should confirm that, under normal operating conditions, condensation does not form on the visible interior surfaces of any framing members or glazing.

Site testing for watertightness#

To check the workmanship of the installation has not compromised the performance of the system in any way, on site watertightness testing of coupling joints should be carried out by a UKAS accredited test laboratory using the CWCT hose test method for water penetration.

A minimum of five percent by length of all critical coupling joints should be tested. Where coupled assemblies of the same type are to be installed across a development, a minimum of two installations should be tested.

For phased developments, the minimum testing applies to each phase.

Testing should be carried out on the first installation on any development or phase before progressing with further installations.

On-site testing may be increased in areas of the UK that are expected to be subjected to severe weather exposure.

If on site watertightness testing reveals problems with workmanship, then these problems should be addressed, and additional testing carried out to confirm satisfactory watertightness performance is achieved before progressing further with the installation.

Last updated: 2nd January 2024

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