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Last edited 16 Aug 2023
Cladding for buildings
What is cladding?
The term 'cladding' refers to components that are attached to the primary structure of a building to form non-structural, external surfaces. This is as opposed to buildings in which the external surfaces are formed by structural elements, such as masonry walls, or applied surfaces such as render.
Building Safety Fund for the remediation of non-ACM Cladding Systems (England only) Registration prospectus, published by MHCLG in May 2020 suggests that: 'A cladding system includes the components that are attached to the primary structure of a building to form a non-structural external surface. The cladding system includes the weather-exposed outer layer or ‘screen, fillers. Insulation, membranes, brackets, cavity barriers, flashing, fixings, gaskets and sealants.'
Whilst cladding is generally attached to the structure of the building, it typically does not contribute to its stability. However, cladding does play a structural role, transferring wind loads, impact loads, snow loads and its own self-weight back to the structural framework. In particular, wind causes positive and negative pressure on the surface of buildings and cladding must have sufficient strength and stiffness to resist this load, both in terms of the type of cladding selected and its connections back to the structure.
What does cladding do?
Cladding is needed to:
- Create a controlled internal environment.
- Protect the building from external conditions.
- Provide privacy and security.
- Prevent the transmission of sound.
- Provide thermal insulation.
- Create an external facade.
- Prevent the spread of fire.
- Generate an 'airtight' building envelope.
- Providing openings for access, daylight and ventilation.
High-quality, well-designed, properly-installed cladding can help maximise thermal performance, minimise air leakage, and optimise natural daylighting. This can help reduce the need for mechanical and electrical building services, and so improve energy efficiency and lower capital and running costs.
- How the building is going to be used.
- Internal and external conditions.
- Local context.
- Planning requirements.
- Building regulations requirements.
- Accessibility and buildability.
- Maintenance requirements.
- Structural requirements.
- Design detailing.
- Control of air leakage.
- Control of condensation.
- Integrity and continuity of Insulation.
- Prevention of water penetration, or provision of drainage.
- Control of thermal movement.
- Spread of fire.
- Ease of installation.
- External attachments and fixings.
- Maintenance, remedial work and renewal.
- Resilience, strength and durability.
Types of cladding
Curtain wall systems are a non-structural cladding system for the external walls of buildings. They are generally associated with large, multi-storey buildings. Typically curtain wall systems comprise a lightweight aluminium frame onto which glazed or opaque infill panels can be fixed. These infill panels are often described as 'glazing' whether or not they are made of glass.
Sandwich panels (sometimes referred to as composite panels or structural insulating panels (SIP)) consist of two layers of a rigid material bonded to either side of a lightweight core, so that the three components act as a composite.
The term ‘patent glazing’ refers to a non-load bearing, two-edge support cladding system. Patent glazing bars provide continuous support along two edges of glazing infill panels (rather than four-edge curtain walling), and are fixed back to the main structure of the building. This system supports its own weight, and provides resistance to wind and snow loading, but does not contribute to the stability of the primary structure of the building.
A rainscreen (sometimes referred to as a ‘drained and ventilated’ or ‘pressure-equalised’ façade) is part of a double-wall construction. The rainscreen itself simply prevents significant amounts of water from penetrating into the wall construction. Thermal insulation, airtightness and structural stability are provided by the second, inner part of the wall construction.
One of the most popular methods of cladding is through the use of timber softwoods, such as western red cedar. This type of wood is relatively knot-free and has a natural resistance to decay and moisture. It can be readily stained or painted and altered to create a range of profiles.
Hardwoods can also be used including oak and sweet chestnut. Both of which contain high tannin levels which can result in leaching and streaking after exposure to the elements. Thermally modified timbers are also being used such as Kebony, Keywood, Platowood and ThermoWood. These softwoods are heated to high temperatures which removes moisture and resins, resulting in a stable and durable material.
A fabric membrane is 'stretched' to form a three-dimensional surface that may be used to create a roof, shading, or decorative component. Sometimes described as 'modern tents', fabric structures use very little material compared to other forms of construction, and are typically translucent, but they provide little thermal mass or insulation and can have a shorter lifespan than some materials.
Shakes and shingle
One of the cheaper forms of cladding is uPVC with white being the cheapest option. It can have fewer detailing requirements than timber and requires less maintenance, although it can discolour with age.
The impact of the Grenfell Tower fire on cladding selection
On 14 June 2017, a fire broke out in Grenfell Tower, a block of social housing flats in North Kensington, London occupied by between 400 and 600 people. The source of the fire is thought to have been a fridge freezer, and the unexpected speed of the fire’s spread is believed to have been contributed to by the recently-installed exterior cladding. Since then, combustible materials have been banned in the external walls of high-rise residential buildings. In particular, this has affected Aluminium Composite Material (ACM) panels, commonly used for cladding buildings, typically as a form of rainscreen, and High Pressure Laminate (HPL) panels.
PAS 9980:2022, Fire risk appraisal of external wall construction and cladding of existing blocks of flats – Code of practice, published by BSI Standards Limited in 2022, defines cladding as a: ‘system of one or more components that are attached to, and might form part of the weatherproof covering of, the exterior of a building.’
It states: ‘Such systems are normally attached to the primary structure of a building to form nonstructural, non-loadbearing external surfaces and can comprise a range of facing materials/cladding panels, including metal composite panels or non-loadbearing masonry, along with insulating materials, rendered insulation systems (ETICS) and insulated core sandwich panels, which are attached to a substrate. Combinations of, for example, cladding panels and insulation form cladding systems and such systems might include cavities, which can be ventilated or nonventilated. The cladding system also encompasses the supporting rails and bracketry, as applicable, to attach the cladding to the building, and cavity barriers where applicable. Systems that constitute the entire thickness of the external wall, by definition, cease to be cladding systems and are the external wall, e.g. curtain walling.’
- ACM cladding.
- BS 8414 Fire performance of external cladding systems.
- Building fabric.
- Curtain wall systems.
- External wall insulation.
- Fire performance of external thermal insulation for walls of multistorey buildings, third edition (BR 135).
- Infill panel walls.
- Metal composite panels.
- Metal profile cladding.
- Natural stone cladding.
- Non-ACM cladding.
- Patent glazing.
- Plastic cladding.
- Sandwich panel.
- Structural Insulated Panels.
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