Why Was Cladding For Buildings Not Fire Tested

The history of high-rise construction in the United Kingdom is marked by a complex interplay between architectural innovation, regulatory oversight, and material science. To understand why was cladding for buildings not fire tested to the standards we expect today, one must look at the evolution of Building Regulations and the testing methodologies that were historically deemed sufficient.

For decades, the industry relied on small-scale component testing rather than full-scale system assessments. This approach often failed to account for how different materials—such as combustible insulation, polyethylene-cored panels, and timber framing—interact when exposed to a developing fire within a ventilated cavity.

At CladdingTesting.com, we frequently encounter building owners who are surprised to learn that their façades, though compliant with the regulations of the time, were never subjected to a rigorous "real-world" fire simulation. This gap in testing has left a significant legacy of risk that property managers must now systematically address.

Key Takeaways#

• Historical Reliance on Bench-Scale Tests: Older regulations often allowed materials to be certified based on small samples (Class 0) rather than full-scale assembly tests.
• The "System" vs. "Component" Gap: Individual components might be non-combustible, but when combined into a rainscreen system with cavities, they can facilitate rapid fire spread.
• Regulatory Ambiguity: Historical guidance in Approved Document B was often interpreted as allowing combustible materials if they met certain surface spread of flame criteria.
• The Role of BS 8414: Large-scale testing via BS 8414 was optional for many years, leading to a lack of data on how specific cladding configurations would behave.
• Mandatory Changes: Post-2017 reforms have shifted the UK toward a "clearer" ban on combustible materials for buildings over 11 or 18 meters, depending on the specific use case.

Defining the Testing Gap#

In the context of UK construction, the question of why was cladding for buildings not fire tested refers to the absence of full-scale system testing (such as BS 8414) for many installed façades. Instead, many systems were installed based on Class 0 ratings, which only measured the surface spread of flame on individual panels, failing to simulate how a fire moves through the internal cavities of a high-rise building envelope.

The core reasons for this lack of comprehensive testing include:

• Reliance on outdated "National Classes" for fire performance.
• Ambiguous wording in Approved Document B regarding "filler" materials.
• Commercial pressure to use lightweight, thermally efficient, but combustible materials.
• A regulatory environment that favored "functional requirements" over prescriptive, rigorous testing of every specific assembly.

The Evolution of Fire Testing Standards#

To appreciate the current landscape, it is necessary to distinguish between reaction to fire and fire resistance. Reaction to fire evaluates how a material contributes to a fire's growth, whereas fire resistance measures how long a system can withstand fire before structural failure or heat transfer occurs.

For many years, the UK building industry relied on the BS 476 series of tests. These were small-scale tests conducted in laboratory conditions. While they provided data on how a single panel might ignite, they could not replicate the "chimney effect" found in modern rainscreen cladding systems, where fire can travel vertically behind the panels through the ventilation gap.

The Class 0 Misconception#

The term "Class 0" is perhaps the most significant factor in why was cladding for buildings not fire tested as a whole system. Class 0 was a legal definition in the Building Regulations, not a single test. It was achieved if a material reached a specific standard in two small-scale tests: BS 476-6 (fire propagation) and BS 476-7 (surface spread of flame).

Many developers and manufacturers believed that if a cladding panel achieved Class 0, it was safe for use at height. However, a panel could have a non-combustible aluminum skin but a highly flammable polyethylene (PE) core. The Class 0 test only looked at the surface; it did not account for the core material melting and fueling a fire once the skin was breached.

Rainscreen Systems and the Chimney Effect#

Modern high-rise buildings typically utilize rainscreen cladding. This involves an outer decorative layer, a ventilated cavity, and an inner layer of insulation attached to the building structure. This design is excellent for moisture management and thermal performance but presents unique fire risks.

If the cladding for buildings was not fire tested as a complete system, the following risks often went undetected:

1. Cavity Spread: Fire can enter the gap between the insulation and the cladding panels.
2. Vertical Acceleration: The cavity acts like a chimney, drawing flames upward at high speeds.
3. Combustible Insulation: Many systems used PIR (polyisocyanurate) or phenolic foam insulation, which, while thermally efficient, can contribute to fire load if not properly protected.
4. Failed Cavity Barriers: If fire breaks are missing or incorrectly installed, there is nothing to stop the flame from bypassing floor compartments.

At CladdingTesting.com, our investigation teams frequently find that even when fire-rated materials were specified, the lack of system-wide testing meant that the interaction between fixings, rails, and panels was never truly understood.

The Introduction of BS 8414#

The UK did eventually develop a rigorous test: BS 8414. This is a large-scale test where a 9-meter-high masonry or steel-frame wall is built, clad in the full system, and subjected to a significant fire load. This test was designed to see if the system as a whole could prevent fire spread.

However, for a long period, BS 8414 was not the only route to compliance. Building Regulations allowed for "Linear Routes," where if individual components met certain criteria, the system was deemed compliant without needing the expensive and time-consuming BS 8414 test. This "desktop study" approach allowed many systems to be installed without ever facing a real flame.

Why Full-Scale Testing Was Avoided#

• Cost: A BS 8414 test can cost tens of thousands of pounds and requires significant lead times.
• Complexity: Testing every possible combination of panel, insulation, and fixing is logistically challenging.
• Regulatory Allowance: If the law allowed for a cheaper, component-based certification (Class 0), commercial entities naturally followed that path.

The Shift Following Major Incidents#

The tragic events at Grenfell Tower in 2017 served as a catalyst for questioning why was cladding for buildings not fire tested more rigorously. It became clear that the reliance on "Class 0" and "desktop studies" was insufficient for high-rise residential safety. The subsequent Hackitt Review highlighted a "race to the bottom" in terms of building safety standards.

Since then, the UK government has introduced the Building Safety Act 2022 and amended Approved Document B. These changes effectively banned the use of combustible materials on the external walls of new high-rise buildings over 18 meters (and introduced stricter requirements for those over 11 meters). The focus has shifted from "reaction to fire" of individual parts to the "non-combustibility" of the whole assembly.

How We Investigate Untested Cladding#

For building owners managing assets constructed before these regulatory shifts, the priority is identifying what exactly is on their walls. Because much of this cladding was not fire tested as a system, a retrospective technical assessment is required.

Our methodology at CladdingTesting.com follows a structured path:

1. Desktop Audit and Document Review#

We begin by reviewing O&M (Operation and Maintenance) manuals, as-built drawings, and fire strategy reports. We look for evidence of BS 8414 testing or BR 135 classification. In many cases, these documents are missing or incomplete, necessitating physical inspection.

2. Intrusive Inspection and Sampling#

We perform "opening up" works. This involves removing small sections of cladding to inspect the internal buildup. We look for:
• The type of insulation (mineral wool vs. combustible foam).
• The presence and condition of cavity barriers and fire stops.
• The material of the cladding panel core (PE, FR, or A2).
• The integrity of the support grid and fixings.

3. Material Laboratory Testing#

If the panel type is unknown, samples are sent to a laboratory for bomb calorimeter testing or thermogravimetric analysis. This determines the calorific value of the material and its likely reaction to fire, providing clarity that the original construction phase lacked.