Glossary · Two-word term
Existing System
In short
the cladding and associated components currently installed on a building
The term "existing system" describes the entirety of a building's current external wall components, including cladding, insulation, and fire barriers. It forms the baseline for technical assessments, safety inspections, and potential remediation works under UK building regulations.
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Existing System
Definition and Scope of the Existing System
In the context of the UK built environment, the term "existing system" refers to the entire assembly of cladding and associated components currently installed on a building’s external facade. While the term is frequently used as a shorthand for the visible outer leaf, in technical and regulatory terms it encompasses the full vertical cross-section of the external wall build-up. This includes the rainscreen or outer cladding panels, the supporting sub-frame or rail system, insulation materials, cavity barriers, fire stops, membranes, and the structural substrate itself, such as concrete, masonry, or steel studwork.
Defining the existing system is the foundational step in any facade assessment. It serves as the baseline against which all subsequent testing, risk assessments, and potential remedial designs are measured. Because many buildings, particularly those constructed between the 1990s and mid-2010s, may lack comprehensive "as-built" documentation, the process of identifying the existing system often requires physical investigation to verify that the components on site match the historical specifications.
The Role of Existing Systems in Cladding Testing
The identification of an existing system is critical during the initial stages of a Fire Risk Appraisal of External Walls (FRAEW). Under the methodology set out in PAS 9980:2022, a competent professional must understand the composition and interaction of the materials within the wall to assess the risk of fire spread. Testing typically begins with a desk study of available drawings, followed by intrusive inspections (often via opening-up works) to confirm the presence and condition of internal components like cavity barriers.
Sampling is a standard procedure when the exact specification of an existing system is unknown. Small sections of the cladding and insulation may be removed and sent to a UKAS-accredited laboratory for material identification or combustibility testing. The data gathered from these tests does not provide a simple "pass/fail" for the building but instead provides the empirical data necessary for a holistic fire engineering assessment of the existing system’s performance in its specific context.
External Wall Systems and Building Fabric
The existing system is rarely a monolithic entity. On complex developments, a single building may feature several different existing systems—for example, a combination of Aluminium Composite Material (ACM) on upper storeys, High-Pressure Laminate (HPL) on recessed balconies, and traditional brickwork on the lower elevations. Each system must be documented separately, as their thermal performance, moisture management, and fire dynamics will differ.
The relationship between the existing system and the building fabric is one of interdependence. The system must manage wind loads, provide thermal insulation, and ensure the building remains watertight. When evaluating an existing system for repair or replacement, professionals must consider how the original installation interacts with the structural frame. Factors such as the condition of the fixings, the presence of galvanic corrosion between dissimilar metals, and the integrity of the vapour control layers are essential considerations that extend beyond the surface-level appearance.
Regulatory Context in England and Wales
Following the introduction of the Building Safety Act 2022 and subsequent amendments to the Building Regulations, the scrutiny of existing systems on "relevant buildings" (typically those over 11 metres or 18 metres in height, depending on specific criteria) has increased. The regulatory framework requires that the Accountable Person or Principal Accountable Person maintains a "Golden Thread" of information regarding the building’s safety.
For many existing systems, this information was historically incomplete. The current regulatory environment necessitates a retrospective gathering of data to satisfy the requirements of the Building Safety Regulator. When an existing system is found to require remediation, any replacement components must comply with contemporary Building Regulations, such as Regulation 7(2), which mandates the use of non-combustible materials (typically European Class A1 or A2-s1, d0) in the external walls of certain high-rise residential buildings. The transition from an existing system to a compliant replacement is a complex legal and technical process governed by these evolving standards.
Existing System
Considerations for Building Owners and Managers
For those responsible for building management—including Resident Management Company (RMC) and Right to Manage (RTM) directors—the existing system represents both a technical asset and a potential liability. Understanding the existing system is the first step in navigating the requirements of the Building Safety Fund or other government cladding schemes.
Managing agents must facilitate access for professionals to conduct intrusive surveys. The outcomes of these surveys define the scope of the "remedial works," a term used when the existing system is judged to require modification to meet modern safety standards. It is important for stakeholders to recognise that the "existing system" includes hidden elements; a building may have non-combustible outer panels but an existing system that is considered high-risk due to the absence of adequate cavity barriers or the presence of combustible insulation behind the panels.
| Component Category | Typical Elements of an Existing System |
|---|---|
| Outer Leaf | Panels, planks, render, brick-slip, or glazing. |
| Support Structure | Helping hand brackets, rails, T-sections, and fixings. |
| Thermal Layer | Mineral wool, PIR, PUR, or phenolic foam insulation. |
| Fire Mitigation | Cavity barriers, intumescent strips, and fire stopping. |
| Moisture Control | Breather membranes and vapour control layers (VCL). |
Common Misunderstandings
A frequent misunderstanding is the belief that the "existing system" refers only to the cladding panels themselves. This leads to the misconception that replacing the outer panels alone will resolve all performance or regulatory issues. In practice, the performance of the system is derived from how the components work in unison. For instance, the air gap (cavity) behind the cladding is a functional part of the system; if this is compromised, the entire system may fail to perform its role in moisture management or fire containment.
Another common confusion relates to the "original" vs "existing" system. While they are often the same, an existing system may have undergone previous repairs or partial replacements that were not documented. Professionals must therefore treat the system as it stands at the time of inspection, rather than relying solely on the original 1990s or 2000s architectural specifications, which may no longer reflect the reality on the ground.
Related Terminology
To accurately discuss existing systems, it is necessary to understand several closely related technical terms:
- Substrate: The structural wall (e.g., blockwork or SFS) to which the existing system is attached.
- Cavity: The ventilated space between the insulation and the cladding panels designed to allow moisture to evaporate.
- As-Built: Documentation intended to reflect the building as it was actually constructed, though often found to be inaccurate regarding existing systems.
- Remediation: The process of altering or replacing an existing system to bring it into alignment with current safety standards.
- Specified System: The proposed new assembly of materials that will replace the existing system during a recladding project.
- Intrusive Survey: The physical act of removing parts of the existing system to inspect the internal components.
Professional assessment remains the only method to determine the specific composition and condition of an existing system. Each building presents a unique configuration of materials and installation quality, requiring site-specific analysis rather than general assumptions based on age or appearance.
Existing System