Answer extracted from the Glazing Insider podcast — listen to the full episode below.
Why do 70% of windows and doors fail certification testing?
The chances of products passing certification testing without any issues are remarkably slim. Around 70% of windows and doors fail per testing visit when manufacturers submit samples for weather, security, and performance evaluations. These failures stem from fabrication errors, component defects, or other manufacturing issues that only surface under controlled testing conditions.
When windows and doors arrive at certification labs, they face rigorous testing protocols that expose problems invisible during standard factory quality checks. As John Warburton explains in the Glazing Insider episode, the failure rate reflects the complexity of fenestration products—each component must function flawlessly, and a single weak point triggers a failure.
Why fabrication and components matter in testing
The high failure rate isn't random. Most failures trace back to specific issues: seals not positioned correctly, components from suppliers that don't meet spec, or assembly problems that manufacturing teams miss during production. The certification process acts as an unforgiving checkpoint that catches what internal quality control may have overlooked.
A window that seems perfectly assembled on the factory floor can fail air-tightness testing, water resistance, or security assessment once it reaches the lab. This is precisely why repeated visits are common—manufacturers address failures, resubmit samples, and work through iterations until everything passes. The 70% failure rate per visit underscores that getting fenestration right demands precision at every stage.
"I think we provide a very, very good service. Customers seem to appreciate what we do. I think we're firm but fair."
John Warburton — Managing Director, ER Certification Ltd. John began his fenestration career in the mid-1980s at a small PVC window fabricator in Lancashire, learning manufacturing from start to finish. Over decades, he progressed through roles in field technical support, exports, product development, and sales at companies including Profile 22, Commolin, Vika, and Epwin. He later joined the Building Research Establishment (BRE) in Watford to help establish certification schemes for windows and doors, and now leads ER Certification Ltd, which he purchased from founder Bill Keaton.
What makes certification testing particularly valuable is that the full episode dives deeper into how certification labs handle edge cases—the unusual configurations or rare manufacturing scenarios that can derail a batch. John Warburton's decades of experience across fabrication and testing means he approaches failures not as simple pass/fail moments, but as feedback loops that help manufacturers strengthen their processes.
See also
What is the biggest change in the fenestration industry over the past 40 years?
The biggest change has been driven by standards and regulations pushing product quality much higher. Products from the 1980s were basic and insecure, but modern fenestration has evolved significantly due to stricter compliance requirements.
How did early experience in PVC window manufacturing during the 1980s shape understanding of fenestration production?
John started at a small fabricator in Lancashire in the mid-1980s making PVC windows during the early days of PVC. He spent his first 18 months learning manufacturing from start to finish, progressing through various roles that provided comprehensive insight into the entire production process.
What is the scope of machinery representation at Fit Show 2025?
Fit Show 2025 features the biggest representative display of machinery ever shown, which is massively important for the industry to see the latest innovations and equipment available.