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Specialist contractors
Site testing
Site testing may be used to check workmanship, occasionally it is used to check design performance. As a check on design performance it is no substitute for controlled testing of a specimen in a laboratory. Lessons learnt from site testing will not be fed in to the design but will only be used to assess options for rectification work.

Site testing to assess wokmanship should be timely. It should be undertaken early in a project if the desire is to improve workmanship, and at the end of construction if it is to prove compliance.

Air leakage testing

Whole building air leakage tests are required by Part L of the Building Regulations (England and Wales). Air leakage arises principally from poorly designed interfaces between cladding packages. A whole building air leakage test checks that interfaces and other sources of air leakage are correctly sealed. Guidance on whole building air leakage testing is given in CWCT Technical Note TN44

Water testing

Water penetration resistance may be tested to check workmanship or design. Workmanship is checked using the hose test whilst design is tested using an improvised cabinet test or in the case of patent glazing and rainscreens a spray bar test. All of these tests are described in the CWCT Technical Note TN41.


Thermal imaging can be a useful way to identify thermal bridges, the location of air leakage and other factors that affect surface temperature of the building envelope. Thermal images have to be interpreted with care to separate the different factors that may lead to variations in surface temperature. The CWCT has published Technical Note TN45 which describes thermography and its use as a diagnostic tool for building envelopes.

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