Fixings

Definition and Technical Scope#

In the context of the UK building envelope sector, the term 'fixings' refers to the specific mechanical devices and components used to secure cladding panels, rainscreen systems, and secondary support structures to the primary substrate of a building. While the term is broad, in professional practice it distinguishes the discrete elements—such as screws, rivets, bolts, and anchors—from the broader assembly. These components are responsible for transferring the loads acting on the external wall, including self-weight and wind pressure, back to the structural frame.

The selection of a fixing is dictated by the chemical and physical compatibility between the component being secured and the substrate, which may be concrete, steel, masonry, or timber. Fixings are typically categorised by their method of engagement: mechanical anchors rely on friction or mechanical interlock, while chemical anchors utilise a resin-based bond. In high-rise applications, the integrity of these components is a fundamental consideration for the long-term stability of the external wall system.

Role in External Wall Systems (EWS)#

Fixings are the critical interface within a multi-layered external wall system. A standard rainscreen assembly generally consists of the external cladding panel, a cavity, a layer of insulation, and a subframe (often aluminium or galvanised steel) which is attached to the building’s structural slab or inner leaf. Fixings are required at every junction of this assembly.

The performance of these components is not merely a matter of structural retention; they must also account for thermal movement. Cladding panels expand and contract due to temperature fluctuations. Consequently, fixing patterns often include a combination of 'fixed points' to provide lateral stability and 'sliding points' or 'floating points' to allow for linear expansion without inducing stress that could lead to panel warping or failure. Furthermore, the material composition of the fixing—often stainless steel or coated carbon steel—is selected to prevent galvanic corrosion, which occurs when dissimilar metals come into contact in the presence of moisture.

Fixings in Testing and Assessment#

In the UK, the assessment of fixings is a standard component of intrusive wall surveys and EWS1 (External Wall System) appraisals. Professionals conducting these reviews typically examine the type, frequency, and condition of the fixings currently in situ. This often involves the use of 'pull-out tests,' where a calibrated device is used to measure the force required to extract a fixing from the substrate. This ensures that the original installation meets the design load requirements specified by the manufacturer.

Testing also scrutinises the 'edge distance' and 'spacing'—the proximity of fixings to the edge of a panel or to one another. If fixings are placed too close to a panel edge, the material may shear; if they are too far apart, the panel may deflect under wind loads. During the replacement of non-compliant cladding systems, the existing fixings and support rails are often assessed to determine if they can be reused or if the entire secondary structure requires replacement to accommodate a new, potentially heavier or differently configured cladding material.

Regulatory and Process Context#

The regulatory framework in England and Wales, governed primarily by the Building Regulations 2010 and the subsequent Building Safety Act 2022, places significant emphasis on the performance of the entire external wall assembly. Approved Document B (Fire Safety) and Approved Document A (Structure) provide the foundational guidance for fixing specification. In buildings over 11 metres (or 18 metres depending on specific triggers), the structural integrity of the cladding system under fire conditions is a key consideration; fixings must maintain their hold even when subjected to thermal stress.

For 'Higher-Risk Buildings' (HRBs), the Building Safety Regulator (BSR) oversees a more stringent 'Gateway' process. During the design and construction phases, the specification of fixings must be documented in the 'Golden Thread' of information. This ensures that there is a clear record of what was installed, who manufactured it, and whether it was installed according to the engineered design. For existing buildings, the assessment of fixings often falls under the remit of a qualified fire engineer or structural engineer as part of a holistic Fire Risk Appraisal of External Walls (FRAEW) conducted to the PAS 9980 standard.

Professional Considerations for Building Stakeholders#

Building owners, Managing Agents, and Residents' Management Company (RMC) directors often encounter the term 'fixings' during the procurement of remedial works or during routine maintenance cycles. It is important to recognise that fixings are not 'universal' components; a fixing designed for a solid concrete slab may be entirely inappropriate for a lightweight steel frame or aerated concrete blockwork.

When reviewing specifications for repair or replacement, stakeholders should ensure that the proposed fixings have undergone relevant third-party testing, such as obtaining an ETA (European Technical Assessment) or UKCA marking. Discrepancies between the design specification and the 'as-built' reality are a common finding in forensic cladding reports, highlighting the need for rigorous quality control during the installation phase.

Common Misunderstandings#

A frequent misconception is that the strength of a cladding system is solely determined by the thickness of the panels. In practice, the system’s resilience is often limited by the capacity of the fixings. A high-performance panel may still fail if the fixings are spaced too widely or if the substrate into which they are driven is of poor quality.

Another misunderstanding involves 'secret fix' versus 'face fix' systems. While face-fixed systems use visible rivets or screws, secret-fix systems use mechanical components hidden behind the panel. It is often assumed that secret-fix systems are purely aesthetic; however, they require a different engineering approach to load distribution and may involve complex rail systems that increase the overall depth of the wall zone. Finally, it is often wrongly assumed that all stainless steel fixings are identical. The distinction between grades, such as A2 (304) and A4 (316), is critical, as A4 grade provides significantly higher resistance to corrosion in coastal or highly polluted environments.

Related Terminology#

Understanding the role of fixings requires familiarity with several related technical terms:

• Substrate: The base material (e.g., concrete, brick) to which the fixing is attached.
• Subframe / Helping Hand: The intermediate grid of rails and brackets that sits between the substrate and the cladding panel.
• Embedment Depth: The distance a fixing penetrates into the substrate, which directly affects its load-bearing capacity.
• Thermal Bridge: A pathway for heat to escape; metal fixings that penetrate insulation can create 'cold spots' unless thermally broken.
• Pull-over Force: The measure of a panel's resistance to being pulled over the head of a fixing during high winds.