Cladding systems

Cladding systems consist of 2 interacting components: the wall system (for example, lightweight timber framing) and the cladding layers. Cladding is a non-loadbearing skin or layer attached to the exterior of the walls. Its main role is to protect a building from water and the effects of weather; secondary roles can include sound, and thermal insulation and fire resistance. Your choice of cladding has a significant effect on your home’s environmental performance, cost, aesthetic appeal and property value.

Cladding can be made from timber, masonry, fibre cement, metal, PVC (polyvinyl chloride), or an increasing range of composite materials that combine 2 or more materials, often with a plastic binder. Many of these options are prefinished, requiring no additional coatings or painting. The performance characteristics of cladding materials vary substantially, and your choice of cladding should be based on a careful assessment of your climate and design needs.

By choosing cladding materials specific to an elevation or exposure, you can often achieve the best in physical performance and aesthetics. For example, in situations where a building’s external envelope does not need to be fully ‘sealed’ (for example, under deep verandas), highly breathable cladding can be an advantage. In areas or elevations with high exposure to sun, wind or rain, a very different approach is required.

Source: Prebuilt. Photo: Dan Hocking

Buildability, availability and cost

The buildability, availability and cost of cladding depends on the system chosen. Common cladding systems such as timber weatherboard or brick are readily available and well known in Australia. Less common or newer materials such as external insulation and finish systems (EIFS) will be less readily available, and you may need to find a builder who can work with your chosen material.

Appearance

There are many types of cladding available, and thus a wide range of textures, colours, styles and finishes. The aesthetic outcome is limited only by the designer’s imagination, your budget, 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 Australian climates, it is preferable to use lighter colours or reflective finishes, especially for roofing. The use of darker cladding elements can be beneficial in colder climates.

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 match materials to specific conditions (for example, impact zones or areas requiring more frequent wash-down).

Structural capability

By definition, cladding is generally non-loadbearing (that is, 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 (for example, 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. The National Construction Code should be consulted for ‘acceptable construction practices’.

Durability and moisture resistance

The durability of a cladding system depends on the materials and finishes used. In some cases, the durability will depend on good maintenance (for example, timber weatherboards will need to be repainted or refinished to stay sound).

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. Install as per the manufacturers specifications.

Thermal mass and insulation

Regardless of its mass, cladding that is fixed to the outside of lightweight insulated frames makes no contribution to thermal performance in terms of thermal mass storage.

Cladding systems often contribute little to overall wall insulation values. However, several composite cladding products include insulation: those with higher R values eliminate the need for bulk insulation between the frame members in very mild climates. Condensation risk can be reduced with adequately designed, correctly specified and installed building membranes and draining cavities. Note that rigid foam insulation board is an impermeable vapour barrier, so it is essential to have drying and drainage cavities for these systems in condensation-prone climates.

Sound insulation

With the exception of masonry veneer (for example, brick, earth, concrete, stone) – which is typically 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 a weighted sound reduction index (Rw) rating or sound transmission class (STC). Individual suppliers will factor in these contributions to calculate typical whole-of-wall ratings.

Fire and pest resistance

Much of Australia is bushfire prone, and each site will need to be individually assessed to determine its bushfire attack level (BAL rating). Your local council can be contacted to provide guidance on zoning and whether your property falls within a bushfire-prone area, as well as what level of BAL is required. Material manufacturers and suppliers will have information on the specific BAL ratings that products comply with, following testing under specified conditions.

Pest resistance generally depends on construction design details rather than cladding properties. Composite cladding systems with soft expanded polystyrene (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.

Toxicity and breathability

Most claddings are nontoxic, but finishes, paints and render can have varying levels of toxicity. Ecolabel websites provide this information and can be used to help locate a preferable alternative. Always check and follow the manufacturer’s instructions for application.

Environmental impacts

The environmental impact of cladding varies considerably between cladding options. When choosing cladding products, consider:

• appropriateness for intended lifespan (for example, some high-impact cladding materials such as steel and aluminium have 100-year life spans; if the expected life of the building might be only 40 years, a lower impact, less durable product might be preferable, although steel and aluminium are easily reusable and recyclable.)
• durability and appropriateness of fixings, seals and joints – their lifespan should match that of the cladding material
• embodied energy
• quantities of each material used (for example, some high embodied energy materials such as steel or aluminium are used in small amounts, and embodied energy per square metre can be comparable to larger amounts of other materials)
• long-term performance – external walls may be the most important variable element in thermal performance in residential construction, with a significant impact on energy bills (Treloar et al. 2000); decisions should be based on more than just construction cost or aesthetics
• finishes such as paints and sealants
• maintenance requirements over lifespan
• emissions, depletions and waste rates during manufacture and on-site installation
• potential for recycling or reuse.

Environmental comparisons of cladding products and materials can be found on ecolabel websites such as Ecospecifier Global, Global GreenTag, Good Environmental Choice Australia, Australian National Life Cycle Inventory Database, Environmental Product Declaration Australasia, and Building Products Information Rating (refer to References and additional reading).

Source: Crawford (2019)

Cladding options

Timber weatherboards: vertical and horizontal

Timber weatherboard has been one of the most common cladding systems in Australia. Performance considerations include:

• availability – various products and profiles are widely available.
• durability – moderate to high depending on species and maintenance. Graded in durability classes ranging from 1 (best) to 4 (unsuitable for external use). Variations are common within these gradings due to sapwood (prone to rot) and heartwood (more durable) content and exposure during milling.
• waterproofness – generally good, but dependent on profile and stability (shrinkage, cupping, splitting, warping). Vertical tongue and groove or lapped systems are more common sources of leaks because joints can open or ‘pop’. Horizontal weatherboard systems are generally more waterproof in rain exposed locations. Natural timber defects (for example, knots) can also compromise waterproofness.
• insulation properties – varies with thickness, sealing and density.
• breathability – high, but can be decreased with paints and finishes. Joint detailing generally allows enough breathing to prevent condensation. An appropriately specified and installed vapour control layer is essential and drainage cavities are important in climates with high condensation risk.
• fire resistance – limited for softwoods, but up to BAL-29 (refer to product technical specifications) for selected hardwood species. Species classification and approved BAL-rated hardwood species information can be provided by the timber supplier or the Timber Development Association. Check with the supplier for a product’s BAL rating.
• finishes – generally painted, oiled or stained. Requires regular retreatment due to natural movement and deterioration. High durability timbers (Class 1) can be left to weather naturally; however, this is not advisable in locations highly exposed to the weather or to low sun angles (particularly west), as repeated cycles of drying and wetting break down even the most durable of species.
• maintenance – high unless left raw. Many timber species are subject to shrinkage, swelling, cracking and rot unless well sealed. Ongoing movement requires regular retreatment once painted.
• toxicity – nontoxic if untreated, but sawdust can be a carcinogen if inhaled – dust management must always be used. Some treatments (for example, copper chrome arsenate; CCA) have known toxicity issues. CCA replacement technologies that use copper derivatives have much lower toxicity. Paints and sealants can have toxicity issues.

Photos: Envirotecture, Ute Wegmann

Environmental considerations include:

• embodied energy – among the lowest of all cladding materials. Embodied energy ranges from low to very low depending on manufacturing process, preservatives and termite treatment. Provides carbon sequestration (with the exception of acetylated timber, a patented preservation technique, though the associated lifecycle durability benefits are likely to offset the initial impact).
• resource depletion – renewable when grown in sustainably managed forests. Plantation forests with their mono-species plantings often fail to establish an ecological balance and exhibit limited biodiversity. The harvesting of timber from old growth forests contributes to the loss of high value biodiversity and the depletion of non-renewable resources. Sustainable forestry needs to be verified by a third party, such as the Forest Stewardship Council (FSC), or the Program for Endorsement of Forest Certification (PEFC). Simply stating that timber comes from a ‘sustainable’ source is no guarantee of actual sustainability.
• reuse and recycling – typically difficult to reuse due to the fixings and splitting risk. Recycling options are generally limited to chipping for mulch although this is not possible for painted or treated products.

Reconstituted wood products

Many reconstituted wood products are made from forestry waste with minimal energy or chemical input, high manufacturing waste recovery and water recycling. These products are among the most sustainable of all cladding options. Try to ensure that forestry waste rather than saw log grade timbers are used and that the product contains no old growth forest products. This can be done by insisting on timber that has a reputable third-party chain of custody scheme, such as FSC (Forest Stewardship Council) or PEFC (Programme for the Endorsement of Forest Certification). Manufacturers should state their product’s sources – if the information is not made available, consider another product. Locally produced materials have reduced greenhouse emission profiles due to reduced transport, and also local economic benefits.

Performance considerations include:

• availability – available in most locations.
• durability – highly durable. Suitable for sites subject to seismic or geotechnical movement.
• waterproofness – high.
• insulation properties – negligible.
• breathability – zero to good (depending on material and finish) with lower condensation risk. Can encourage mould growth (by providing nutrients) if exposed to regular moisture. An appropriately specified and installed vapour control layer is essential and drainage cavities are important in climates with high condensation risk.
• fire resistance – good, typically BAL-29 (refer to product technical specifications).
• finishes – may be painted or left raw – this is product specific. Available in a diverse range of patterns, shapes and finishes.
• maintenance – moderate if painted, but often does not require painting, depending upon the individual product selected. Good surface and dimensional stability reduce frequency of maintenance. May be primed, but if left raw will weather to a natural hardwood silver colour over time.
• toxicity – often nontoxic, but check each product, or look for a Global GreenTag. Natural timber resins are used to bond particles under high temperature and pressure. Paints and sealants applied after installation may have toxicity issues.

Environmental considerations include:

• Embodied energy – among the lowest embodied energy cladding materials currently available in Australia. Also sequesters carbon.
• Resource depletion – virtually nil when product is made from certified plantation forest waste.
• Reuse and recycling – generally not recycled if painted. Limited reuse is possible, but often not implemented due to low cost of new materials.

Plywood sheeting

Plywood sheeting is a very common wood product with a relatively low cost. Performance considerations include:

• availability – available throughout Australia.
• durability – moderate to very high depending on grade, species, glues and maintenance. Low grade plywood requires similar protection to timber. Exterior grade plywood made specifically for cladding is quite durable.
• waterproofness – high depending on finish and joint detailing.
• insulation properties – limited.
• breathability – generally low, but variable with thickness and grade. An appropriately specified and installed vapour control layer is essential and drainage cavities are important in climates with high condensation risk.
• fire resistance – poor to average; unlikely to be more than BAL-19 (refer to product technical specifications).
• finishes – generally painted, oiled or stained.
• maintenance – low to moderate depending on grade and applied finishes.
• toxicity – generally low, but adhesive type should be checked to ensure it is low or zero VOC.

Environmental considerations include:

• embodied energy – low to moderate. Manufacturing process and glues make embodied energy higher than natural timber. Plywoods are still net carbon sequesters.
• resource depletion – renewable when plantation grown.
• reuse and recycling – plywood cladding is highly reusable, but cannot be recycled. It should be screwed, not glued, to support reuse.

Fibre cement

There are several variations of fibre cement materials, some manufactured in Australia, others imported from Europe or China. The different characteristics of each require evaluation so that the most appropriate is selected.

Manufactured in a strict factory-controlled environment, most fibre cement products have high sustainability credentials. However, considerable variations can occur between brands and manufacturing plants depending on waste recovery rates, water sourcing and recycling, energy efficiency (particularly the recovery of energy from the autoclave during production), and transport impacts.

Fibre cement is typically produced as planks, weatherboards or sheets. Sheet products are generally thinner and therefore less material intensive, but often have higher site waste rates, particularly on complex designs and shapes.

Fibre-cement raw sheet with cellulose, sand and cement

This is the most common material, made without asbestos in Australia since the late 1980s (earlier products contain asbestos). Performance considerations include:

• availability – commonly available due to high level transportability.
• limitations – cannot be used in direct contact with ground.
• durability – highly durable and dimensionally stable. Suitable for sites subject to seismic or geotechnical movement.
• waterproofness – high. Varies according to thickness, applied finish and quality of joint finishing.
• insulation properties – poor insulator.
• breathability – good (depending on finish) with very low condensation risk. Can be subject to surface mould growth if exposed to regular moisture. An appropriately specified and installed vapour control layer is essential and drainage cavities are important in climates with high condensation risk.
• fire resistance – excellent, can be combined in systems up to BAL-FZ (refer to product technical specifications).
• finishes – available in a diverse range of patterns, shapes and finishes.
• maintenance – low maintenance due to stability, but requires painting/sealing to maintain waterproofness. Stamped or sawn patterns applied during manufacture can add aesthetic variation.
• toxicity – nontoxic. Coatings, paints and sealants can have toxicity issues.

Environmental considerations include:

• embodied energy – generally medium to low. Varies with volume, cement content, manufacturing efficiency and transport distances from factory to markets.
• resource depletion – plantation-grown cellulose reinforcing fibre is renewable. Cement is non-renewable, and is a finite resource with high embodied energy. Sand and fines are abundant, but non-renewable.
• reuse and recycling – generally not recycled due to finishes. Limited reuse is possible, but often not implemented due to low cost of new materials and deconstruction damage.

Photo: Quentin Chester

Prefinished fibre-cement sheet

These are generally imported products, with high quality finishes applied in the manufacturing process. Performance considerations include:

• availability – reasonably available due to high transportability
• limitations – cannot be used in direct contact with ground
• durability – highly durable and dimensionally stable. Suitable for sites subject to seismic or geotechnical movement
• waterproofness – high. Varies according to thickness and finish
• insulation properties – poor insulator
• breathability – good with very low condensation risk. An appropriately specified and installed vapour control layer is essential and drainage cavities are important in climates with high condensation risk.
• fire resistance – excellent, can be combined in systems up to BAL-FZ (refer to product technical specifications).
• finishes – available in a diverse range of patterns, shapes and finishes
• maintenance – virtually zero maintenance due to longevity of pre-finish. Various colours and patterns applied during manufacture provide aesthetic variation
• toxicity – nontoxic. Paints and sealants can have toxicity issues.

Environmental considerations include:

• embodied energy – generally low, but transport impacts increase this somewhat. Varies with volume, cement content and manufacturing efficiency
• resource depletion – plantation-grown cellulose reinforcing fibre is renewable. Cement is non-renewable, and a finite resource with high embodied energy. Sand and fines are abundant, but non-renewable
• reuse and recycling – generally not recycled due to finishes. Limited reuse is possible, but often not implemented due to low cost of new materials and deconstruction damage.

Magnesium oxide cement sheet

This is an increasingly common material, currently all imported. Performance considerations include:

• availability – reasonably available in major centres, less so in regional areas
• limitations – few, can be used in direct contact with ground which enables it to be used as part of slab-edge insulation and subfloor wall cladding
• durability – highly durable and dimensionally stable. Suitable for sites subject to seismic or geotechnical movement
• waterproofness – high. Varies according to thickness and finish
• insulation properties – poor insulator
• breathability – good (depending on finish) with very low condensation risk. Can be subject to surface mould growth if exposed to regular moisture. An appropriately specified and installed vapour control layer is essential and drainage cavities are important in climates with high condensation risk
• fire resistance – excellent, can be combined in systems up to BAL-FZ (refer to product technical specifications)
• finishes – mostly in smooth sheet finish only
• maintenance – low maintenance due to stability, but pending manufacturer’s instructions may require painting to maintain warranty. Usually smooth faced
• toxicity – nontoxic. Paints and sealants can have toxicity issues. Dust from cutting should be suctioned or supressed, and normal particulate breathing protection worn.

Environmental considerations include:

• embodied energy – generally low, usually sequesters carbon dioxide during the curing process. Uses low energy magnesium cements, but commonly has a small amount of fibreglass reinforcing mesh
• resource depletion – magnesium oxide ore is a common resource, but is mined and therefore non-renewable. Sand and fines are abundant, but non-renewable
• reuse and recycling – generally not recycled due to finishes. Limited reuse is possible, but often not implemented due to low cost of new materials and deconstruction damage. Requires careful handling during demolition as glass fibres (if released during rough handling) can be carcinogenic.

Brick

Brick, used in either brick veneer, reverse brick veneer or double brick constructions, is the most common cladding material in Australia. Performance considerations include:

• availability – most common cladding system
• durability – highly durable on well-designed footings. Less suited to seismic loads and reactive soils
• waterproofness – low. Requires wide cavity and specially designed ties, flashings and cavity drainage. Cavity ties and weep holes must be cleared of mortar droppings on completion
• insulation properties – poor insulator, but has thermal lag due to its high thermal mass
• breathability – high with very low condensation risk when an appropriately specified and installed vapour control layer is used, due to well ventilated, wide cavity
• fire resistance – excellent, but structural capacity during fires is under-used in non-loadbearing cladding applications (for example, brick veneer)
• finishes – diverse range of (unpainted) colours and finishes
• maintenance – lowest maintenance if unpainted and not rendered; otherwise moderate
• toxicity – nontoxic. Paints and sealants can have toxicity issues.

Environmental considerations include:

• embodied energy – very high in quantities used
• resource depletion – abundant, but finite resource
• reuse and recycling – increasingly recycled into new bricks (cradle to cradle) or crushed for fill. Use of high-strength mortars prevents reuse, but bricks laid with low-strength mortar (for example, 6:1:1 sand:cement:lime mortar) are often cleaned and reused.

Steel

Steel cladding comes in a wide variety of profiles with varying base metal gauge and structural capacity. Most steel cladding materials are made from high-tensile base metal coated in a zinc-aluminium alloy with modified polyester, with a long life and a good warranty, in a variety of colours. Steel products are also available that use weathering to produce a thin stable oxidised coating, which protects the steel from further corrosion, and looks like rusty steel. Coated steels are available in a variety of exposure condition ratings. Higher durability products have fluoropolymer modified coatings with increased thickness zinc-aluminium alloy coatings underneath.

Photo: © AndyRasheed/eyefood

Performance considerations include:

• availability – available in all regions of Australia
• durability – durability is very high; galvanised corrugated steel can last more than 100 years on a building and is a material highly sought after for decorative reuse. However, it must be installed carefully, with fixings and flashings that are compatible for corrosion and lifespan. Scratches, pencil marks and swarf from cutting can lead to early corrosion
• waterproofness – among the most waterproof of cladding materials
• insulation properties – zero insulation
• breathability – steel cladding is a vapour impermeable material and its excellent conductivity makes it highly susceptible to dew-point formation and water vapour condensation. It is essential that an appropriately specified vapour control layer and drainage cavity is installed in strict accordance with manufacturers’ instructions
• fire resistance – high in both roofing and walling applications, up to BAL-FZ (refer to product technical specifications).
• finishes – a range of standard colours and finishes including galvanised and zinc/aluminium corrosion treatments. A range of standard baked enamel pre-finish colours is available
• maintenance – very low. Steel finishes are very durable and, while coloured finishes often fade slightly, they rarely require repainting for maintenance. Because steel expands, adequate tolerances must be left at joins and junctions
• toxicity – nontoxic.

Environmental considerations include:

• embodied energy – high
• resource depletion – steel is a non-renewable resource
• reuse and recycling – steel sheeting is highly reusable and 100% recyclable. Current products include up to 40% recycled content.

Aluminium

Aluminium cladding has a similar range of profiles to steel, but also includes a folded weatherboard product. It is more corrosion resistant than steel. Aluminium cladding comes in a wide variety of cold formed profiles with varying base metal gauge and structural capacity.

Performance considerations include:

• availability – available in all regions of Australia
• durability – durability is very high due to corrosion resistance of the material itself (rather than protective coatings). Life span and corrosion compatibility of fixings and flashings is essential. Careful installation is required
• waterproofness – among the most waterproof of cladding materials
• insulation properties –zero insulation
• breathability – aluminium is a vapour impermeable material and its excellent conductivity makes it highly prone to dew-point formation and water vapour condensation. It is essential that an appropriately specified vapour control layer and drainage cavity is installed in strict accordance with the manufacturers’ instructions
• fire resistance – good up to moderate heat exposure, will not pass BAL-FZ (refer to product technical specifications). Should not be used in plastic composite cladding in any fire risk situation
• finishes – generally powdercoated in standard colours but for special orders any colour can be supplied
• maintenance – low. Powdercoated finishes generally have a life expectancy of 15 years and, although fading is common, they rarely require repainting for protection
• toxicity – nontoxic.

Environmental considerations include:

• embodied energy – highest of any cladding. Most appropriate in highly corrosive environments where products with lower embodied energy have a reduced life span. Aluminium sourced from smelters using renewable energy is low carbon (for example, New Zealand aluminium is produced with hydro energy). Likewise, recycled aluminium products typically have a reduced carbon profile by as much as 75%
• resource depletion – aluminium is an abundant but non-renewable resource
• reuse and recycling – aluminium cladding is highly reusable (if screw fixed) and 100% recyclable.

Poly-timber composite board materials

Poly-timber cladding is manufactured from a mix of materials, typically wood or bamboo waste, or sawdust combined with a plastic binder. Typically, these are manufactured to look like natural or stained timber.

Performance considerations include:

• availability – available in most regions of Australia
• durability – moderate to high due to stability of the core material
• waterproofness – very waterproof
• insulation properties – zero insulation
• breathability – none. It is essential that an appropriately specified vapour control layer and drainage cavity is installed in strict accordance with the manufacturers’ instructions
• fire resistance – poor, unlikely to have a BAL rating above 12.5 (refer to product technical specifications).
• finishes – generally emulates raw or stained timber
• maintenance – low. Generally have a life expectancy of more than 15 years, although some fading can be expected, they rarely require repainting
• toxicity – nontoxic. Consider products made using recycled plastic material.

Environmental considerations include:

• embodied energy – moderately high due to the plastic component, much lower if recycled plastic such as polythene (recycled milk bottles) or PVC recycled from windows or containers) is used.
• resource depletion – plastics made from fossil fuels are a non-renewable resource
• reuse and recycling – 100% recyclable.

External insulation and finish systems (EIFS)

External insulation and finish systems (EIFS) use rigid foam insulated boards as a substrate behind site-applied render. The most common form is expanded polystyrene (EPS) foam approximately 50mm thick with an acrylic render external skin usually 6 to 8mm thick. EPS has significant pollution problems (small particles break off and escape into the local environment). Safer and higher performance foams are the dense closed cell foams such as extruded polystyrene (XPS), polyisocyanurate (PIR) and polyurethane (PUR) foam boards. Generally, the thicker the foam, the higher the R value and the better the system will work.

EIFS are usually finished with a variety of rendered or site applied finishes that can include high embodied energy polymers.

Performance considerations include:

• availability – easily available in major and regional centres, remote sites may be more difficult
• durability – some systems based on EPS can be damaged by cockatoos, and if not installed correctly may leak; in cool climates can allow condensation to form on the inside if not installed over a cavity
• waterproofness – generally good; ensure correct installation details at corners and around openings
• insulation properties – varies with thickness of base foam board, but additional insulation is most often required in all except the mildest climate zones/li>
• breathability – none. It is essential that an appropriately specified vapour control layer and drainage cavity is installed in strict accordance with the manufacturers’ instructions
• fire resistance – the BAL rating of each system will be stated by the manufacturer, and it is common to be rated to BAL-19 or in a few cases, BAL-29 (refer to product technical specifications). However, the kind of foam will be a determining factor here, and if you want the lowest possible risk regardless of your BAL rating, specify a system that uses a PIR foam rather than EPS (which is highly flammable)
• finishes – various render finishes, smooth to moderately textured
• maintenance – minimal if installed correctly, generally more than 15 years from the top colour coating
• toxicity – imported foams may include ozone depleting substances that are banned in Australia.

Environmental considerations include:

• embodied energy – many foam products contain high impact greenhouse gases, which can increase their embodied energy relative to other insulation materials
• resource depletion – foams are generally derived from fossil fuels
• reuse and recycling – not available at this time in Australia
• panel size - when panels are cut on site, waste beads of foam can escape into the environment. Ensure that the building design uses standard panel sizes.

PVC

PVC cladding is available in a range of profiles, colours, textures and low, or no, maintenance finishes.

Performance considerations include:

• availability – in most major centres
• durability – durable in the sun to various specification levels, untested beyond about 30 years
• waterproofness – excellent
• insulation properties – none, additional insulation required as with any other thin cladding material
• breathability – none. It is essential that an appropriately specified vapour control layer and drainage cavity is installed in strict accordance with the manufacturers’ instructions
• fire resistance – rigid PVC, which cladding is made from, is naturally fire retardant because of the chlorine content. It is slow to ignite and self-extinguishes when flame is removed. Vinyl cladding can be used in bushfire prone areas up to BAL29 (refer to product technical specifications) where used 400mm above ground or deck level
• finishes – prefinished in a variety of colours and textures, including faux wood grain
• maintenance – low, at least on a 30-year cycle
• toxicity – although PVC resin emissions are among the lowest of any fossil-fuel-based plastic, most plastics rely on international supply chains and many (for example, Epoxy, PUR, PIR, EPS, XPS, PVC, polycarbonate) include toxic precursor ingredients

The processes that create these polymers take place in heavily regulated and controlled environments and once the final form of the plastics is created it is typically inert and harmless. This is because once the precursor ingredients (monomers) are combined, they create highly durable and stable long-chain polymers that provide benefits such as rigidity and durability. Third-party environmental certification systems for PVC products – Best Environmental Practice PVC, Global GreenTag or GreenRate – ensure that the products are the best available technology and do not contain toxic stabilisers or plasticisers.

Environmental considerations include:

• embodied energy – PVC has a higher embodied energy than timber, but less than aluminium
• resource depletion – PVC is currently derived from fossil fuels
• reuse and recycling – fully recyclable. Although PVC recycling rates have been low in the past due to cost and complexity, major advances are being made as markets are being established and waste streams delineated.

Innovative sustainable cladding products

Innovative products using sustainable materials such as hemp stem fibre, agricultural waste (straw, husk) or post-consumer waste (paper) are constantly emerging. These products use various methods to ensure waterproofness and durability, and typically have a lower environmental impact than traditional products, particularly with regard to embodied energy. Some are even ‘carbon positive’.

Modular wall panels are available that are made from wheat and/or rice straw fibres with high acoustic and fire resistance ratings. The manufacturing process combines extreme heat and compression in a dry extrusion process to form the solid panel core. A natural polymer in the straw fibre is released during the procedure, and a water-based PVA (polyvinyl acetate) glue is used to encapsulate the finished core with a high strength recycled kraft (bitumen sealed) paper liner. The result produces no toxic waste and no water or gas is used during the manufacturing process.

Another product uses a blend of cement and wood waste (sawdust), rice husks, and other low value materials, all combined into a high value block or panel, which can be used as cladding with no additional applied finishes required.

Regulatory standards

The National Construction Code addresses specific aspects of cladding:

• timber weatherboard cladding
• fibre cement planks and weatherboard cladding
• sheet wall cladding
• eaves and soffit linings
• 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 additional testing and certification is common with new environmentally preferred systems as they arrive in the market. Consumers and specifiers should always check a material’s compliance credentials.

Reducing the risk of condensation

Generally, the purpose of cladding is to protect the building membrane, which is the final water resistant barrier and it should be assumed that the cladding (render in the case of EIFS) will leak at some stage of the building’s life. An appropriate vapour-permeable building wrap is called ‘Class 4 wrap’ in Australian Standard AS4200.1.

A ventilated cavity is required behind all cladding systems to ensure that when its gets wet, air movement allows it to gradually dry out. Bulk insulation can be added in between wall framing but consideration needs to be given to moisture movement. In some Australian climates an internal vapour control layer may be required.

A ventilated cavity will decrease the effectiveness of any insulation, and this needs to be taken into account when calculating the total R value of the wall.

The following design strategies could overcome condensation-related problems related to the fixing of cladding. Seek expert advice and follow the cladding manufacturer’s installation advice when considering these systems.

Source: Adapted from Weathertex

Specification of a vapour-permeable membrane

Fix a suitable vapour-permeable membrane to the outside of the frame to allow water vapour to escape. This membrane should have low vapour resistance (less than 0.5MNs/g) and high waterproofness in accordance with Australian Standard AS/NZS 4200.1:2017 Pliable building membranes and underlays. It should be stretched taut to prevent bulk insulation, installed later inside of the frame, from breaching the condensation cavity.

Condensation within the wall structure creates ideal conditions for rot and mould growth, which can lead to substantial structural damage and health issues. Reflective foil membranes may not achieve sufficient permeability to resolve this problem.

Where reflective layers are required under cladding for fire purposes, they should be specified and installed according to the manufacturer’s requirements for your climate.

Allow for a cavity

Create a cavity a minimum of 9mm deep between the outside of the vapour-permeable membrane and the inward face of the cladding material. This cavity should allow:

• downward migration of the condensation that might form when the cladding reaches dew-point
• in-cavity air movement and ventilation to remove water vapour-laden air as it emerges from the membrane.

Cavities should be formed with vertical spacers or battens fixed to studs through the permeable membrane in accordance with Australian Standard AS/NZS 4200.1:2017 Pliable building membranes and underlays. Leave gaps in spacers to allow lateral air movement in case of cavity blocking.

Install a vented cavity closer at the top and bottom of the cavity (including above openings) that prevents insects, pests or burning embers from entering, but allows condensate or water (bottom) and vapour (top and bottom) to permeate. If in a bushfire-prone area, the vented cavity closers must satisfy BAL requirements.

Several proprietary systems are available, but you can also use a stainless steel mesh of similar grade and opening size to that used for termite protection.

Installation of cladding

Fix the cladding through the battens with fixings that are long enough to allow adequate penetration into the stud to meet the cladding manufacturer’s specifications.

• Eco-comparison websites
  –    Australian National Life Cycle Inventory Database
  –    Building Products Information Rating
  –    Ecospecifier Global
  –    Environmental Product Declaration Australasia
  –    Global GreenTag
  –    Good Environmental Choice Australia
• Australian Building Codes Board (2019). National Construction Code 2019, Volume 2.
• Australian Building Codes Board (2019). Condensation in buildings handbook.
• Bluescope Steel, Install cladding.
• Carre A (2011). A comparative life cycle assessment of alternative constructions of a typical Australian house design. Report for Forest and Wood Products Australia prepared by RMIT Centre for Design, Melbourne. 
• Consumer Building and Occupation Services (2019). Condensation in buildings – Tasmanian Designers’ Guide,[PDF] Tasmanian Government.
• Crawford RH (2019). Embodied energy of common construction assemblies
  (Version 1.0). The University of Melbourne, Melbourne.
• CSR Bradford, Consequences of condensation.
• CSR Bradford, Wall wrap for lightweight clad construction.
• Cumming A (2019). Thin skin: getting cladding right. ReNew, Sanctuary Magazine.
• National Timber Development Council (2001). Environmentally friendly housing using timber: principles, 1st edn, Forest and Wood Products Research and Development Corporation, Brisbane. 
• National Timber Development Program (2003). Environmental benefits of building with timber, Technical report, issue 2. Forest and Wood Products Research and Development Corporation, Melbourne. 
• Treloar G, Fay R, Love P and Iyer-Raniga U (2000). Analysing the life-cycle energy of an Australian residential building and its householders. Building Research and Information 28(3):84–195. 

Learn more

• Read Condensation for advice on installing cladding correctly to avoid problems associated with condensation 
• Read Brickwork and blockwork to understand the options for brick or concrete cladding
• Look at Insulation for more ideas on how to keep your home warm in winter and cool in summer

Authors

Original author: Chris Reardon 2013

Updated: Dick Clarke 2020