Last edited 06 Apr 2017

Cladding for buildings

Cladding.jpg

Contents

[edit] Introduction

The term 'cladding' generally 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 themselves, such as masonry walls, or applied surfaces such as render.

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.

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.

Cladding is often pre-fabricated in panels that are attached to the structural frame of the building, and some cladding systems can be purchased 'off the shelf'.

Cladding systems may include additional components, such as windows, doors, gutters, roof lights, vents and so on.

The nature of cladding selected for a particular building will depend on considerations such as:

  • How the building is going to be used.
  • Internal and external conditions.
  • Durability.
  • Local context.
  • Planning requirements.
  • Buildability.
  • Appearance.
  • Availability.
  • Budget.
  • Maintenance requirements.
  • Structural requirements.

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. Poor design detailing or installation may compromise cladding performance and can even lead to cladding collapsing or cladding panels pulling away from the structure.

When selecting or designing a suitable cladding, designers might pay particular attention to:

  • 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.
  • Ease of installation.
  • External attachments and fixings.
  • Cleaning.
  • Maintenance, remedial work and renewal.
  • Resilience, strength and durability.

[edit] Types of cladding

The NBS Building libraries categorises claddings and coverings as:

H10 Patent glazing
H11 Curtain walling
H13 Structural glass assemblies
H14 Precast concrete and glass lens / paver rooflights / floor lights / pavement lights / security panels
H20 Rigid sheet cladding
H21 Timber weatherboarding
H22 Plastics weatherboarding
H30 Fibre cement profiled sheet cladding / covering
H31 Metal profiled / flat sheet cladding / covering
H32 Plastics profiled sheet cladding / covering
H40 Glass fibre reinforced concrete panel cladding / components
H41 Glass fibre reinforced plastics cladding / features
H42 Precast concrete panel cladding / features
H43 Metal composite panel cladding / features
H51 Natural stone slab cladding / lining / features
H60 Plain roof tiling
H61 Fibre cement slating
H62 Natural slating
H64 Wood shingle and shake roofing
H65 Single lap roof tiling
H67 Metal single lap roof tiling
H71 Lead sheet coverings / flashings
H72 Aluminium strip / sheet coverings / flashings
H73 Copper strip / sheet coverings / flashings
H74 Zinc strip / sheet coverings / flashings
H75 Stainless steel strip / sheet coverings / flashings
H90 Tensile fabric coverings
H91 Thatch roofing
H92 Rainscreen cladding

Some of the more common types of cladding are described below.

[edit] Curtain walling

Curtain wall systems are a non-structural cladding systems 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.

See Curtain wall systems for more information.

[edit] Sandwich panels

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.

See Sandwich panel and Metal composite panels for more information.

[edit] Patent glazing

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.

See Patent glazing for more information.

[edit] Rainscreen

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.

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.

See Rainscreen for more information.

[edit] Timber cladding

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. Western red cedar is generally sourced from North America (predominantly Canada), but it is starting to be grown in the UK. Other softwoods that are often used include Douglas fir and Scottish and Scandinavian larch.

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. Hardwood cladding also requires pre-drilling which can add to installation time and costs.

Thermally modified timbers are also being used such as Kebony, Keywood, Platowood and ThermoWood. The softwoods are heated to high temperatures which removes moisture and resins, resulting in a stable and durable material.

Some of the most common laying styles are as follows:

[edit] Square edge

A uniform thickness, usually between 12-18 mm, whilst widths of boards vary from 125-225 mm.

[edit] Feather edge

Boards are tapered across their width, producing a rustic, rural aesthetic.

[edit] Shiplap

Has a shaped front face and profile so that the top of each board fits behind the bottom edge of the adjacent board, providing a neat finish.

[edit] Tongue & groove

Produce a uniform look that suits contemporary houses. They have a flat face and, in the absence of any overlapping, the way the groove covers the tongue of the board below keeps out rain.

[edit] Metal profile cladding

Sheets are manufactured in a range of corrugated and other profiles, such as trapezoidal, sinusoidal or half-round. The profiles are manufactured from sheets fed through banks of forming rollers.

For more information see Metal profile cladding.

[edit] Tensile fabric coverings

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.

See Fabric structures for more information.

[edit] Brick slips

Brick slips are thin layers of masonry and are of similar appearance to conventional bricks. They are available in a variety of styles and colours.

See Bricks for more information.

[edit] Tile hanging

The traditional method of cladding a property is through the use of tiles. The addition of which can add character to older style properties.

[edit] Shakes and shingle

Shakes and shingles are produced from split logs and look similar to timber tiles. Shakes are typically split from the log using a chisel and mallet whilst shingles are sawn off.

For more information, see Shingle roofing.

[edit] uPVC

One of the cheaper forms of cladding is uPVC with white being the cheapest option. It often has fewer detailing requirements than timber and requires less maintenance, although it can discolour with age.

For more information, see uPVC weatherboarding and Plastic cladding.

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