Wall Cladding: Design Criteria, Material, and Types

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Cladding is the process of layering one material over the other to protect a building from natural elements like wind and rain. It also provides insulation and noise control and boosts the aesthetic appeal of a building. Cladding can be carried out on exterior walls as well as on interior walls.

Criteria for Design of Cladding  

The design of cladding must take account of the following physical and statutory criteria:

1. Loads

The cladding does not carry the weight of the building, but individual bays of cladding must carry their own weight. They must also resist wind loads and impact, both external and internal. All these forces must be transmitted to the structural frame via suitable connections.  

2. Relationship between Cladding and Frame

The connections between the cladding and frame must accommodate any dimensional ‘lack of fit’ between frame and cladding. This is particularly important when a precisely manufactured cladding system is secured to a reinforced concrete frame, as the frame will be constructed to a lower standard of accuracy.  

The design must also allow for movements:  

• In the frame – usually deflections, but also creep and long-term shrinkage of concrete.
• In the cladding – usually induced by changes in temperature or moisture content.  

3. Weatherproofing 

The cladding is expected to restrict rainwater and snow. Waterproofing can be achieved in a variety of ways.  

Cladding systems can generally be divided into three groups:  

A. Face-sealed

The material is largely impermeable, and joints are intended to be waterproof.  

B. Overlapping

The material is largely impermeable, and the sheets or panels overlap so that water cannot penetrate.  

C. Internally drained

Some amount of water penetrates the cladding material or the joints but is controlled within the cladding and channeled back to the exterior.  

4. Thermal Insulation

The design of all heated buildings must include thermal insulation. In some systems, it is an integral part of the cladding construction. In others, it may be incorporated in a separate inner lining or sandwiched between inner and outer layers. In combination, weatherproofing, insulation, and lining must also prevent or control condensation. This may require vapor barriers and/or ventilation.

5. Acoustic Insulation

Specific levels of sound insulation may be required for buildings in noisy environments, such as near airports. Heavy cladding systems possess inherently good noise attenuation. Lightweight systems can have their sound performance improved by internal linings.  

6. Fire Resistance

Specific fire resistance periods are required for walls near boundaries and escape routes. Fire barriers must be incorporated within voids where cladding passes compartment walls and floors and certain other areas.  

In many cladding systems, the design criteria can only be met by the outer cladding acting in conjunction with internal linings or backup walls.  

7. Other Design Criteria

The design should also consider the availability of materials, manufacturing lead times, and speed of installation. If a building is to be constructed quickly, the program will be partly dictated by the cladding system chosen.

With some systems, the building becomes considerably weatherproof on completion of an inner lining or backup wall, permitting internal services to operate simultaneously as the outer cladding is being installed. 

Criteria for Selection of Cladding Material  

The cladding materials are selected at an early stage in the development of the design to suit the architectural concept. The normal criteria for the selection of cladding material are:

1. Appearance

To create a particular visual impression or aesthetic look of the building to complement the function of the building.

2. Cost

A limited budget will restrict the choice of materials or systems.

3. Weight

Heavy cladding systems (generally masonry and precast concrete) may affect the cost of the frame. Large panels may be impractical on congested sites or where there is no craneage.

4. Robustness

Some materials are vulnerable to impact or vandalism. Designs may use lightweight cladding at a high level and plinth walls of brickwork or concrete to cope with ill-treatment at ground level.

5. Durability

When a cheap cladding system is proposed, savings in initial construction costs must be balanced against anticipated lifespan and likely maintenance requirements.  

Types of Cladding Materials

1. Masonry

Masonry is one of the most common forms of cladding.  

It is a strong, durable cladding, and a more expensive option of cladding that is employed in ‘high class’ work. It is widely used for low or medium-rise buildings. Thin panels of natural stone have been used to clad both low and high-rise buildings.

2. Precast Concrete

The use of precast concrete panels to form the external envelopes of buildings became popular in the 1950s and ’60s. Panels were commonly used as load-bearing components within structural systems and were convenient for cheap, rapidly erected flats and offices.  

Current practice favors non-load-bearing panels in a more up-market role, taking advantage of their perceived solidity and ability to take both modern and traditional surface finishes.

3. Glass-Reinforced Plastic (GRP)

GRP is a light, resilient material that can be molded in various shapes. It is popular for streamlined, modernistic structures but can also be used to imitate traditional forms. 

The principal constituent materials are polyester resin and glass reinforcement. An outer ‘gel coat’ of resin may be used as a decorative coating.

4. Glass-Reinforced Cement (GRC)

GRC cladding is manufactured by spraying a mixture of sand/cement mortar and alkali-resistant glass fibers onto a mold. It may be an intermediate between precast concrete and GRP in form and function. However, some installations have experienced problems of deterioration and deflections.

5. Metal Panels

Metal panels are often used on hi-tech style industrial or commercial buildings. Many systems incorporate insulation between outer and inner skins, presenting a ‘finished’ appearance on each surface. 

6. Profiled Sheets

Profiled cladding sheets are formed from pre-galvanized steel, aluminum, or fiber cement compositions. These materials are generally cheap, light, and quick to erect. 

These sheets are normally used in conjunction with separate inner linings. However, some manufacturers assemble sandwich panels, generally with foamed insulation between two steel skins.

7. Glazed Screens and Curtain Walling

A glazed screen is a large vertical area of glass installed by coupling together a number of individual windows. Curtain walling is a mixture of glazing units, opening vents, and opaque panels secured to a grid of mullions or transoms.  

Most modern glazed screens and curtain walling have frames and grids of aluminum, although steel is also used sometimes.

8. Timber Boarding

Timber cladding is extensively used in the United Kingdom to clad architectural features such as fascias, dormers, and gables. New boards are stained rather than painted. In places where white or colored boarding is required, it has become common practice to use polyvinyl chloride (PVC) extrusions that imitate timber. 

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