Cladding is typically made from wood, metal, plastic (vinyl), masonry or an increasing range of composite materials. It can be attached directly to the frame or to an intermediate layer of battens or spacers to prevent condensation and allow water vapour to escape.
Cladding systems include horizontal or vertical boards, sheet materials or smaller overlapping panels such as shingles and tiles. Each system uses different methods to prevent wind and rain entering through the joints, and each system’s effectiveness varies depending on wind direction and speed and the degree of exposure to rain.
The range of textures, colours, styles and finishes available means that the aesthetic outcome is limited only by the designer’s imagination, council regulations or extreme site conditions.
Apart from aesthetic considerations, the colour of external cladding influences its capacity to absorb or reflect heat. In most climates, it is preferable to use lighter colours or proprietary reflective finishes, especially for roofing.
Well designed applications of darker cladding elements can be beneficial in colder climates.
Texture or profile
Most cladding materials have a distinctive profile or texture that can create horizontal, vertical or angled patterns and shadow textures. Often a well designed blend of cladding materials can offer both a pleasing appearance and a better matching of materials to specific conditions (e.g. impact zones or areas requiring more frequent wash-down).
Cladding selection presents an opportunity to reduce the overall environmental impact of a home by choosing environmentally preferred materials and systems.
Research indicates that external walling is the most important variable element in residential construction (Treloar and Fay 2000). Research findings vary significantly because standardised methodologies and metrics are yet to be agreed or adopted, but sufficient studies have been conducted to clearly indicate the characteristics of preferred generic materials.
Life cycle assessment (LCA) considers the total environmental impact of a material over its life cycle including environmental emissions and depletions from the materials and the processes used to make it, maintain it, and dispose of or recycle it at the end of its life.
While rigorous LCA of various materials at a generic level is often available, it is seldom so for individual products. When choosing products, apply life cycle thinking to address the following considerations:
• appropriateness for intended life span (e.g. some high impact cladding materials have 100 year life spans when the expected life of the building might be only 40 years; a lower impact, less durable product would be preferable)
• durability and appropriateness of fixings, seals and joints: their life span should match that of the cladding material
• quantities of each material used (e.g. some high embodied energy materials such as steel or aluminium have very thin sections, and embodied energy per square metre can be comparable to other materials with thicker sections)
• finishes such as paints and sealants, which can have a greater impact than the product itself and should be given equal consideration
• maintenance requirements over life span, which can equal or exceed the production impact of the cladding material; LCA of the whole wall system is the best approach when available
• emissions, depletions and waste rates during both manufacture and on-site installation, which vary significantly between products; ‘cradle to gate’ assessments (i.e. from resource extraction to factory gate) provided by manufacturers often examine manufacturing impacts only, whereas ‘cradle to grave’ LCA examines whole of life emissions and depletions
• designing, choosing and specifying to maximise potential for recycling or reuse (e.g. screw fixing rather than gluing can facilitate easy removal and reuse at end of life providing screw heads are not filled)
• whole system performance (i.e. effectiveness of cladding in protecting other elements from weathering and condensation)
• contribution to thermal performance (e.g. insulation, reflectance, emissivity)
• transport considerations (distance, weight, volume), which can add substantially to embodied energy.
Note that actual data can vary significantly between studies and products.
Source: Adapted from Lawson 1996
Indicative embodied energy content for some typical cladding systems.
By definition, cladding is generally non-loadbearing (i.e. it doesn’t carry roof or floor loads). However, some sheet cladding systems can have a structural bracing role in lightweight framing applications when appropriately fixed to the frame (e.g. structural plywood, reconstituted timber, fibre reinforced cement sheeting). The fixing requirements for bracing cladding can have significant implications for visual appearance, waterproofing, condensation, ventilation and drainage.
Cladding systems often contribute little to overall wall insulation values.
Several composite cladding products include insulation: those with higher R-values (the measure of a material’s resistance to heat flow) can eliminate the need for bulk insulation between the frame members in many climates. With adequately designed and correctly installed vapour cavities, condensation risk can be reduced or eliminated. Note that EPS (expanded polystyrene) is a vapour barrier so it is essential to have drying and drainage cavities for these systems in condensation-prone climates.
Regardless of its mass, cladding that is fixed to lightweight insulated frames makes no contribution to thermal performance in terms of thermal mass storage because it is on the outside of the building and uninsulated.
The use of high mass cladding in lightweight framing systems (e.g. brick veneer) can actually decrease thermal performance because thermal lag can maintain higher temperature differentials across insulation layers well beyond normal diurnal cycles (e.g. west-facing brick veneer walls).
Where the internal loadbearing element is high mass (e.g. reverse brick veneer or water filled containers between frame elements), transparent cladding materials such as glass with high solar heat gain coefficients (SHGC) can contribute to passive solar heating. In these cases, the whole wall must be passively shaded. In these applications, both the insulation values and transparency of the cladding material are critical considerations, particularly in cooler climates where night-time heat loss can offset daytime heat gain. Trombe walls rely on the combined action of thermal lag of the mass and insulation from the air gap. Unwanted convection is controlled with openable vents at the top and bottom of the wall.
Additional insulation can also be gained in cooler climates through the use of double glazing (higher SHGC, lower R-value) or multi-celled polycarbonate (lower SHGC, higher R-value). In temperate climates, louvred glass allows cooling breezes and night sky radiation to passively cool thermal mass.
With the exception of brick veneer — which is a high mass, high thickness system — cladding generally provides limited sound insulation. The contribution of denser products and foam insulation backed products is usually indicated as an Rw (weighted sound reduction index) rating or STC (sound transmission class). Individual suppliers factor in these contributions to calculate typical whole-of-wall ratings.
Vermin resistance is generally dependent on construction design details rather than cladding properties. Composite cladding systems with EPS foam backing can harbour rats and birds if access for burrowing is not eliminated.
Non-timber systems and most reconstituted timber systems are not subject to termite attack but inadequate detailing can allow termites to access a timber structure undetected. All timber cladding materials are subject to termite attack unless treated.
Building Code of Australia Class 1 and 10 Buildings, section 3.5.3, Wall cladding, addresses specific aspects of cladding under Application, Timber weatherboard cladding, Fibre cement planks and weatherboard cladding, Sheet wall cladding, Eaves and soffit linings, and Flashings to wall openings.
Providing cladding meets the minimum standards within each relevant category and meets the appropriate Australian Standards, it is deemed to comply. Innovative cladding systems may require additional testing and certification. This is common with new environmentally preferred systems.