Stopping

Definition and Technical Application#

In the context of the UK cladding and facade industry, 'stopping' refers to the process of halting or ceasing an action or progression. While the term is occasionally used in its general sense to describe the cessation of works on-site, it holds specific technical significance regarding the management of moisture, air, and fire within the building envelope. In a structural and remedial context, stopping relates to the physical interruption of a pathway or the termination of a specific component’s installation.

Within the external wall system (EWS), stopping is rarely a standalone procedure but rather a critical phase in the sequence of assembly. For instance, when installing cavity barriers or fire stopping—two distinct but related concepts—the objective is to stop the passage of flame and smoke through concealed spaces. In moisture management, 'stopping' may refer to the use of flashings or closures to prevent the ingress of water into the insulation layer or the structural sub-frame. Precision in these stopping points is vital to ensuring that the performance of the system aligns with the original design specifications.

Stopping in Testing and Remediation#

During the testing and investigative phase of a cladding project, particularly during an EWS1 assessment or a PAS 9980 appraisal, the concept of stopping is frequently encountered in the context of 'fire stopping'. This refers to the materials and methods used to seal penetrations in fire-rated walls and floors, as well as the junctions between the facade and the internal structure. If a surveyor identifies that stopping is absent or incorrectly installed, it is typically noted as a deviation from the expected design standard.

In repair and replacement works, stopping points are established to ensure that new materials are integrated correctly with existing elements. When a cladding system is replaced in phases, 'temporary stopping' is often required. This involves securing the edges of the newly installed system against weather and wind loading at the end of each working day or at the conclusion of a specific phase. This temporary measure prevents the exposure of the inner building fabric to the elements while the project is in a transitional state.

Building Fabric and External Wall Systems#

The building fabric relies on a continuous line of defence against external stressors. Stopping represents the intentional termination of these lines. For example, in a ventilated rainscreen system, the cavity is designed to allow air to circulate and moisture to drain. However, this cavity must be 'stopped' at specific intervals—such as compartment floors and party walls—using cavity barriers that allow for ventilation during normal conditions but expand to seal the gap in the event of a fire.

The efficacy of these stopping measures is dependent on the compatibility of the materials used. If a stopping material reacts chemically with the cladding panel or the vapour membrane, the integrity of the building fabric may be compromised over time. Therefore, the selection of stopping components is a matter of detailed architectural specification and engineering.

Regulatory Context in England and Wales#

In England and Wales, the regulatory framework governing the use of stopping materials is primarily dictated by the Building Regulations, specifically Approved Document B (Fire Safety) and Approved Document L (Conservation of fuel and power). Following the introduction of the Building Safety Act 2022, there is an increased emphasis on the 'Golden Thread' of information, which requires a detailed record of how stopping measures have been designed and installed.

For buildings over 11 metres (and particularly those over 18 metres), the requirements for fire stopping and cavity barriers are rigorous. The regulations do not merely require that stopping is present, but that it has been tested as a complete system. Building Control bodies and Accountable Persons must ensure that any stopping measures implemented during remediation are supported by appropriate certification, such as UKAS-accredited laboratory test data. The transition from design to installation is monitored through mandatory inspections, ensuring that the 'as-built' stopping matches the 'as-designed' fire strategy.

Considerations for Building Owners and Managers#

Building owners, Managing Agents, and Residents' Management Company (RMC) directors must understand that 'stopping' is a critical element of building maintenance and safety. It is not a decorative feature, but a functional one that is often hidden behind the external panels. During a cladding replacement project, the cost and complexity of the works are frequently driven by the requirement to install or rectify stopping measures that were either missing or incorrectly installed during the original construction.

It is common for professionals to refer to 'fire stopping' and 'cavity barriers' interchangeably in casual conversation, but for those responsible for building safety, the distinction is important. Fire stopping generally refers to static seals in service penetrations, while cavity barriers are specific to the voids within the cladding system. Understanding these nuances helps directors when reviewing tenders or progress reports from contractors, as it allows for a more informed assessment of the scope of work being undertaken on their building.

Common Misunderstandings#

A frequent misunderstanding is the belief that stopping needs to be an airtight seal in all locations. In ventilated cladding systems, 'stopping' the cavity at every junction would prevent the necessary airflow that keeps the building dry and prevents interstitial condensation. The technical challenge lies in using 'open-state' stopping, which allows for airflow under normal conditions but ceases that airflow instantly in the event of heat exposure.

Another misconception is that stopping materials are universal. In reality, a material that is effective at stopping moisture (such as a standard mastic) may have no fire-resistant properties, and a fire-stopping material may not be weather-rated. Using the wrong type of stopping for a specific application is a common cause of building envelope failure. Professional assessment is always required to ensure that the material chosen is fit for the specific environment and regulatory requirement of the building in question.

Related Terminology#

• Cavity Barrier: A component designed to close a concealed space to prevent the passage of fire and smoke for a specified period.
• Fire Stop: A seal provided to close an imperfection of fit or design tolerance between elements or components, to restrict the passage of fire and smoke.
• Intumescent: A substance that expands as a result of heat exposure, commonly used in stopping measures to fill gaps when triggered by fire.
• Compartmentation: The division of a building into fire-resistant cells to limit the spread of fire; stopping is the primary method of maintaining this division where services or cavities cross boundaries.
• Flashing: A thin layer of waterproof material that stops water from entering a junction between different building components.