A glass façade might look flawless when installation is complete. However, appearance alone cannot tell you how it will perform during inclement weather. That is where CWCT testing comes in.
For architects, developers and contractors, water tightness is a vital part of commercial glazing performance. Testing helps check whether installed glazing and its joints resist water penetration as intended. It can also highlight issues while they are easier to address.
What is CWCT testing?
CWCT stands for the Centre for Window and Cladding Technology. The organisation publishes standards and technical guidance for building envelopes, including curtain walling, glazed screens and cladding.
In everyday project discussions, “CWCT testing” often refers to checks carried out against relevant CWCT test methods. These may include laboratory performance tests or on-site water penetration tests. The exact method depends on the system, specification and stage of the project.
For more detail on the industry framework, see the Centre for Window and Cladding Technology.
Why does water tightness matter in commercial glazing?
Commercial glazing faces changing weather throughout the year. Rain can be driven towards façades by wind, while joints and interfaces must cope with movement and regular use.
A well-designed system manages water through a combination of seals, drainage routes, framing and carefully detailed connections. If those elements are poorly installed or damaged, water may reach places it should not.
Water penetration can affect internal finishes and disrupt the use of a building. As a result, checking performance before handover is an important part of quality assurance.
How is commercial glazing tested for water tightness?
There is no single test for every façade. The testing team selects a suitable method based on the glazing system and project requirements. Two common approaches to on-site testing are hose testing and spray bar testing.
1. Hose testing
A hose test directs a controlled water jet along selected joints. The aim is to assess the resistance of permanently closed joints and check installation workmanship. Inspectors monitor the internal side for unwanted water penetration.
This method is commonly associated with CWCT Section 9. It is not automatically suitable for every opening joint or porous construction, so the correct test arrangement matters.
2. Spray bar testing
A spray bar uses a series of nozzles to create a continuous flow of water over a defined area. It can be appropriate for systems with opening joints or other details where a hose test is unsuitable.
The relevant procedure and acceptance criteria must be agreed for the project. The test should follow the specified standard rather than an improvised water spray.
The British Fenestration Rating Council’s CWCT testing guidance explains the different on-site methods and their applications.
What happens during an on-site CWCT water test?
Although arrangements vary, a typical process follows a clear sequence:
- Confirm the specified test method, location and acceptance criteria.
- Prepare access, water supply and the test area, with the relevant joints and internal surfaces available for inspection.
- Apply water in accordance with the chosen test method.
- Inspect for evidence of unwanted water penetration and record the findings.
- If an issue is found, investigate the cause, complete remedial work and arrange further testing where required.
Testing should be planned at a suitable stage. For example, finished internal linings may hide the very areas that need to be inspected.
What if glazing fails a water tightness test?
A failed test does not automatically mean the whole glazing system needs replacing. The first step is to identify where the water entered and why.
Possible causes include gaps in seals, incomplete joint detailing, blocked drainage paths or issues where the glazing meets another building element. Once the cause is understood, the responsible team can agree the repair and any necessary retest.
This is one reason early checks are valuable: they can help prevent small defects from becoming larger problems after occupation.
Does passing a CWCT test guarantee a leak-free building?
No test can guarantee performance in every future condition. A test assesses the selected area against a defined method and set of criteria at a particular time.
Good design, correct specification, careful installation and ongoing maintenance still matter. Testing is one part of a wider quality assurance process, not a replacement for it.
Planning commercial glazing? Start with the details
Water tightness is easier to manage when it is considered early, from system selection and interface design through to installation and inspection.
At Visual Concept, we work on a wide range of commercial glazing solutions, helping bring architectural designs to life. You can also explore our guide to curtain walling systems for more on modern glazed façades.
If you have a project in development, contact the Visual Concept team to discuss your glazing requirements.