A cladding buyers guide

An example of modern Australian architecture in this wood cladded structure shot on a beautiful, warm sunny day.
Wood can make for a very nice, natural finish, but can be higher maintenance than other cladding types. Image: Christopher Freeman via iStock
Building cladding is not just for aesthetics; it is an integral part of a building’s envelope and needs to be carefully selected to ensure the best performance. Lance Turner looks at cladding options and the pros and cons of each material type.

Cladding’s most important role is as a weatherproofing layer to prevent the outside elements—rain, wind and dust—from damaging the internal structure of the walls. It’s also an important part of the aesthetics of a building: it’s the outer skin that you see. One final role is as pest exclusion.

Not all construction systems need cladding. Blockwork systems such as bricks, strawbale, mudbrick, rammed earth and autoclaved aerated concrete (AAC, e.g. Hebel), don’t need cladding, although some do need rendering for weather sealing. But, if desired, even these systems can have cladding added, either at the time of the build or later.

Unless it’s used purely for aesthetics, cladding forms part of the building’s wall system and the whole wall system must be evaluated as one entity to ensure thermal, structural and aesthetic requirements are met.

This introduction to cladding highlights important features to consider, and looks at the different cladding types and materials to help you evaluate the pros and cons of each and where you might use them. It’s not intended to replace advice from a building architect or designer, but rather to help you better understand the factors to consider when making a choice.

Cladding features

Water resistance

It goes without saying that the finished envelope must have water resistance to prevent water ingress into the structure which would cause damage. Cladding materials may be naturally waterproof, such as metal or plastic composites, or may be porous and need to be sealed, such as wood. Materials that need to be sealed not only require higher maintenance, but may also be compromised should the sealant coating degrade or be penetrated, although the impermeable membrane behind them should prevent water penetrating past the cladding material itself.

Rot and pest resistance

Some materials, especially natural materials, are more prone to damage by pests such as rats, mice and insects and attack from mould, mildew and fungus. Materials that are subject to such attack, such as in damp locations or country areas with high pest levels, need to be rot and pest resistant.

Fire resistance

In bushfire-prone Australia, especially as the climate changes, fire resistance can be a critical feature of any cladding material. Any cladding will need to meet the BAL (bushfire attack level) for your site, so if you are in a bushfire zone then you are going to be limited in the products you can select. Non-flammable materials such as steel and fibre-cement sheet generally have high BAL ratings (when installed and sealed correctly). Some materials—for example, some composites—that might seem less flame-resistant can have quite high BAL ratings when installed as per specifications, so check the ratings.

One thing to consider is that BAL ratings are for current conditions. As the climate warms and fires become more intense, BAL ratings may increase in some areas. Immediate surrounds (e.g. combustible materials close to the home) have a large effect on BAL ratings of a particular site, but it may still be prudent to aim for cladding with a BAL rating higher than your site currently requires. Increased BAL may mean higher costs (e.g. using a more fire-resistant species of wood).

Wind load ratings

In high wind areas, you must consider wind load ratings. Some claddings have a maximum spacing between fixing points for high wind areas that may be less than the typical stud spacing, so check this. Not all claddings carry a cyclone rating; if your site is prone to cyclonic winds, you must use a suitably rated cladding material.

Weatherboards are easy for the DIYer to replace. The boards on the left were replaced in a couple of days by one person with basic tools, allowing insulation and vermin proofing to be added to the wall. The old boards were cut down to remove rotted sections for reuse in other projects. The boards on the right are on a west-facing wall and cop the brunt of the weather. Some will need to be replaced, others may be salvageable.
Ease of installation/repair

Some materials are simpler to install than others; for example, some will need special manufacturer-supplied finishing profiles at corners and edges to ensure that warranty, weather resistance and other specifications are met. Other materials may require special clips for installation, rather than simple screws or nails, especially those that use a ’hidden’ fixing system. This can add to the cost of installation.

Can the material be drilled, nailed or screwed with minimal risk of cracking? Some materials like fibre-cement sheets are more likely to split if you nail or screw too close to the edge or end. This can make them harder to fasten if, for example, you have to butt join two boards at a wall stud. In this case, you would cut one board short of the stud and fasten the two board ends together with the manufacturer’s recommended joiner, but this can mean slightly more wastage and effort during installation.

You might think that most cladding materials are similar in weight for a given area, but that certainly isn’t the case. While some materials, such as PVC weatherboards, are quite light, others, such as fibre-cement sheet and Corten and other ‘ageing’ steels, can be much heavier and more difficult to handle. If you are DIYing, this may be an important consideration, especially if you are fitting the cladding by yourself, as it will limit where you can safely and easily install the cladding. With heavy materials, a large wall may require several hundred kilograms of cladding—not an insignificant load and a considerable effort to move around and lift into place.

Some cladding systems can be difficult and more time-consuming to repair, especially if they use interlocking boards or panels. To repair a very damaged board halfway down a wall, you may need to remove all boards from the top down to the damaged board. This is particularly so for hidden fixing systems, where the screws for the damaged board are underneath the board above.

Thermal properties

The thermal properties of cladding can vary widely, from virtually a zero R-value for materials like sheet steel, through to quite high R-values for insulated PVC weatherboards and insulated panels. If your home is performing poorly thermally due to lack of wall insulation and your house is in need of recladding, you may be able to solve both by using cladding with a good level of insulation.

Breathability

Not all cladding systems are suitable for all construction types. Cladding systems that are not breathable (non-permeable), such as steel sheet, require a ventilated cavity to prevent condensation build-up, whereas vapour-permeable materials don’t. A ventilated cavity can be as simple as adding battens to the studwork to space out the new cladding from the rest of the framing and insulation. All ventilated cavities should be sealed both top and bottom with vermin mesh to prevent unwanted pests from entering the cavity.

A permeable material can be rendered non-permeable if painted or rendered. A common sign of such an issue is bubbles forming under paintwork on permeable cladding such as wooden weatherboards.

Trapping unwanted moisture vapour inside a wall cavity can result in condensation forming, leading to mould damage. Consult a knowledgeable designer or builder and/or the product manufacturer for correct installation recommendations.

Bubbling in painted weatherboards is a sign of moisture buildup. Paint can make breathable (permeable) materials like wood into non-permeable ones, causing such problems.
Environmental footprint

Some cladding options make use of waste materials that would otherwise be sent to landfill. Recycled plastic composites are one example—these use waste plastic and usually waste wood fibre for stiffness. By reusing materials, these sorts of products have a much lower embodied energy and hence carbon footprint than virgin materials; however, they may also use resins or adhesives which have their own environmental costs.

Also consider recyclability. Composite materials are often not recyclable at end of life. Some manufacturers will take back leftover new materials such as plastic/wood fibre composites for recycling into new products, but some composites like fibreglass are generally not recyclable.

Materials that are fully recyclable at end of life (of either building or material) have a reduced carbon footprint each time they are recycled. For example, metals such as steel that have a high embodied energy initially are recyclable almost endlessly, reducing their carbon footprint each time they are recycled.

Regardless of their recyclability, materials that have degraded will often end up in landfill, as degradation can reduce the quality of the material to the point where it can no longer be recycled.

While some materials, like wood, are theoretically biodegradable at the end of their useful life, in reality this often isn’t the case if they’re coated in layers of paint or other sealants. If you choose a natural material like wood, then you should consider the coating you will use on it or try to source wood species that are weather resistant without treatment (provided they also meet other environmental criteria such as sustainability in harvesting).

Deconstruction is becoming more common nowadays, where the home is disassembled piece by piece, rather than just being demolished (where a bulldozer flattens the home in a big mess). Materials that can be removed easily and with minimal damage are more likely to end up at a secondhand building materials supplier to be reused. This may be a consideration far down on your list of criteria, but it is worth thinking about.

To get the best environmental result, look for environmental certifications of the materials used in the cladding—although these can be difficult to ascertain as manufacturers and suppliers often give limited information.

There are a number of different certifications, including Global GreenTag (globalgreentag.com), GECA (good environmental choice, geca.eco) and Green Tick (greentick.com). For a list of all eco labels that apply in Australia, see bit.ly/ELI-AU.

For wood products, opt for local timber that is recycled/reclaimed, or is from agroforestry (timber that has often had another use on a farm, providing a wider range of social, economic and environmental benefits than plantations or traditional forestry) or well-managed (preferably FSC) plantations. If these aren’t available, look for certifications, such as FSC and PEFC (FSC is preferred), from Australian or New Zealand forestry; avoid timber from overseas, particularly from countries where monitoring may be suspect. Fair Wood is a recent initiative that sources sustainable timber, or check Mullum Creek’s timber guide at bit.ly/MC-TPG.

For treated timbers, look for low-toxicity treatments that have been tested to be such—materials safety datasheets (MSDS) should be available if the product is chemically treated. Avoid CCA treated timber, for example.

One source of certification information is the Ecospecifier website (ecospecifier.com.au) where you can search on particular material types or certifications. A search for cladding materials returned a limited number of materials with any form of certification, so clearly the industry has more work to do in this area. However, the Ecospecifier information may not be complete, so check out a product’s manufacturer specifications for the latest certification information.

Paintability

Some materials have the colour as part of the material and need no external finishes, whereas others require painting on a regular basis. Not all materials can be painted, so if you think you may want a change of colour scheme down the track, then a material that is paintable is necessary. This doesn’t mean that you will need to use materials such as wood as many other materials can be painted successfully; even colour-coated materials like Colorbond can be painted at a later date. Be aware that some materials require specialised (usually expensive and toxic) paints. And some materials, such as those made of plastic composites that contain predominantly polypropylene or polyethylene are not paintable.

Wall cladding made of different sizes natural stone bricks. Colors are shades of red and gray. Background and texture.
Stone and brick tiles can enhance an ordinary blockwork wall. They are available in a range of sizes, colours and patterns. Image: Luca Piccini Basile via iStock

Selecting cladding

You are replacing the cladding on your home or looking at a new build, so which cladding to choose? Consider the features you need, along with aesthetics, maintenance requirements and cost.

If building new, then your architect/designer will have some suggestions that suit the look and feel of the house design. Make sure that their suggestions match your requirements regarding the level of maintenance required and sustainability credentials. Any good designer will ask for your input on cladding at design stage.

For retrofits, you will likely want to choose a cladding system that complements the existing building structure. For example, if you have a 1920s weatherboard home, you probably won’t want to clad it in a modern, vertical format cladding, but rather, something a bit closer to the original boards—though the choice is yours to make.

You may also want your home to match the look of surrounding buildings. A home that looks different can be a talking point, but the novelty may wear off and make it harder to sell at a later date. Different material types and colours can also suit different locations. Homes surrounded by nature often look much better when they blend into the landscape.

There’s nothing to say that you can’t have different cladding systems on different walls. An example might be vertical boards for most of the home, with a weathering steel feature wall. You might also use different cladding on different storeys of the home.

Maintenance must also be considered. High-maintenance materials such as wooden boards that need regular painting, not only cost money on an ongoing basis, they also cost you time and inconvenience (having a painter spend days sanding the old paint back on your home with a power sander can be a real irritation after a few hours!). And those hand-oiled bare boards might look gorgeous now, but when you have to re-oil them every year or so, they can become a burden. Also consider wall orientation. West-facing walls are subject to greater weathering than other orientations, so generally need more frequent maintenance, so low- or zero-maintenance materials are a better option for them.

High maintenance requirements increase the likelihood of maintenance being forgotten or deferred due to cost or lack of time, which can result in accelerated degradation of your cladding. This is particularly the case for homes with difficult access to some wall areas. If you can’t access the upper walls of a two-storey home without climbing gear or a cherry picker, then you really want cladding that needs little or no maintenance.

Cost is also a factor in cladding selection. It can be worth spending a bit more upfront to get materials that will last longer and need less maintenance. For example, wooden weatherboards are cheap and readily available, but they need regular painting and will rot if moisture invades them. Replacing them with a more robust material such as a plastic composite board or wax/wood composite like Weathertex may cost more, but will last a great deal longer—probably the lifespan of the home itself.

If your budget is constrained, then you might want to select a cladding option that lets you do the home one section at a time. Recladding in steel usually requires that the whole house be done at once to ensure a neat, even result, with consistent weathering. Weatherboards on the other hand (regardless of material type), can more easily be done in sections as time and budget permits.

Installation costs will vary, partly depending on the type of cladding and material chosen. For example, weatherboards generally take longer than sheets to install. Some materials need to be predrilled before nailing/screwing, so this adds to the installation time and hence cost. And some materials are far more expensive per square metre than others. To compare two similar materials which come in different sizes, you’ll need to use the square metre coverage of those materials for cost comparison.

Cladding types and materials

The range of cladding materials is vast, with a lot of crossover between types, such as panels that look like groups of weatherboards. To help manage the range available, we will group cladding types into four broad categories and then look at the materials in each category a little more. The four categories we look at are sheet materials, boards, shingles/tiles and insulated cladding.

1. SHEET MATERIALS

Sheet materials can be made from wood, steel, fibre-cement or even plastic.

Wood sheets

Wood sheet cladding includes treated and untreated plywood (treated timber is always softwood; hardwoods don’t need to be treated), and other engineered timber products.

Wood sheet products are cost-effective and quick to install and, being cross-laminated, where alternating layers have their grains running at right angles to each other, they are impact resistant, durable and may even be structurally rated. They are suitable for most situations if selected correctly, but will need regular painting, varnishing or oiling, so maintenance is likely medium to high.

Fire resistance is relatively low and they may not be BAL rated at all or may require additional coatings or treatments to achieve BAL ratings.

Toxicity of engineered timber products is generally low, but it does vary with treatment and glues used. For treated products, unless the material can be reused at end of life, it will generally be sent to landfill.

One example is Shadowclad, a plywood sheet product made from plantation pine that is available as flat or grooved sheets, in natural and primed finish. The pine is treated to H3 level, the minimum level of preservative required to protect the timber from attack by decay fungi and insects, including termites. It uses a LOSP wood treatment (light organic solvent preservative, a treatment with similar termite and weathering resistance to CCA, just without the heavy metals) and a formaldehyde resin for bonding: formaldehyde resins can cause respiratory irritation and other health effects if formaldehyde concentrations in air exceed 3ppm—although this is far less likely to occur from cladding than it is from interior materials such as MDF and chipboard.

Metal sheets

Metal sheet products come in a wide range of profiles and finishes. The most common finish is Colorbond, a baked-on painted finish over mild steel sheet. This is available in profiles including conventional corrugated, mini corrugated, square corrugated, ribbed and even a weatherboard-like profile.

Steel sheets are also available in other finishes, such as galvanised (the steel is hot dipped in almost pure zinc) and Zincalume (similar to galvanised sheet, except an alloy of 55% aluminium, 43.5% zinc and 1.5% silicon is used, which gives much better protection than pure zinc). Like Colorbond, these materials are also available in a range of profiles. Galvanised and Zincalume sheets can be painted, but don’t need to be and are usually used as-is, with the metal coating acting as protection for the steel.

Another steel product becoming more popular is ’weathering’ steel. This is a special alloy of steel which is used uncoated. It forms a surface rust over time, which protects the rest of the steel underneath. The special alloy prevents the usual destructive rusting that damages other steel mixes such as mild steel. Weathering steel is often called Corten steel, after the most popular product of the same name. Weathering steel is available in flat sheets, often quite thick (3mm or so) and also in profiles such as corrugated.

Other metal sheet products include copper, brass, stainless steel and aluminium sheets. Copper, brass and stainless steel are uncommon due to high cost, but they are available in some interesting panels, such as those from Architectural Panel Systems Australia.

Aluminium is usually in the form of composite panels. Aluminium composite panels (ACPs) consist of aluminium on one or both sides of the panel with a core that is usually of plastic (often polyethylene). Aluminium panels were the cause of the Grenfell Tower disaster in the UK where many people died. The tower had an external foam layer, then an air gap, then the aluminium cladding panels. In the fire, the plastic core of the cladding melted, which, combined with the external foam insulation and a gap between the two that produced a chimney effect, rapidly fuelled the fire, causing it to engulf most of the building. We do not recommend the use of ACPs with plastic cores.

However, there are also fire-resistant (very difficult to ignite) and non-combustible aluminium honeycomb cored ACPs, such as the Fairview Vitracore G2 range. These are generally used for commercial buildings but may occasionally be found on domestic builds.

Fibre-cement products

Traditionally, fibre-cement products are simple flat sheets ranging in thickness from 4mm to 18mm or so in thickness. They consist of fibre-reinforced cement, making them fairly strong, impact resistant and weather resistant, and of course they are pest resistant and non-combustible. However, they are also heavy for their size, especially for the thicker sizes. Fibre-cement sheet is normally painted or coated to prevent moisture ingress.

In recent years, fibre-cement sheet has evolved and now includes narrow sheets that are used like weatherboards (these may be smooth or have an embedded pattern) as well as pre-finished sheets in a range of colours. Examples of modern fibre-cement products include CSR’s Cemintel and James Hardie’s Scyon Matrix panels.

Magnesium oxide boards

Magnesium oxide boards are similar to fibre-cement sheet, but have some advantages in that they are made from the very abundant mineral magnesium oxide, along with a fibre reinforcement such as wood fibre or fibreglass mesh. They have a lower embodied energy than cement-based sheets and are available in thicker sizes for greater strength. Magnesium oxide board is also lighter per unit volume than cement sheet and is non-combustible. One disadvantage is that magnesium oxide is hygroscopic (it absorbs and retains water from the air) which can contribute to moisture problems, so check the grade and specifications. Magnesium oxide board is also generally imported from China, so transport emissions will be higher than with locally produced materials.

Plastic sheets

Plastic sheets come in a range of materials and formats. At their most basic, they are simple solid plastic sheets, usually of materials like HDPE (polyethylene). These are often general-purpose panels which can also be used as cladding. A typical example of these is Plaspanel from Builda Panels, a 100% recycled panel available in a range of colours and thicknesses and designed for general-purpose building applications.

Another interesting plastic panel system is the polycarbonate Danpal VRS (ventilated rainscreen system) which uses hollow core Danpalon sheets and matching trims, brackets and accessories to provide a facade that can range from completely transparent through to opaque, depending on the sheets selected.

With all plastic sheets, one issue to be aware of is thermoplasticity—the softening of the plastic with heat. Dark colours can become very hot in the sun, with boards potentially losing strength and even deforming over time.

Fibre-cement sheet has evolved in recent years to include pre-finished sheets in a range of colours and textures. Cement sheet is strong, pest and rot proof, and extremely fire-resistant. Here is part of the range from Cemintel (CSR) Images: CSR
2. BOARD MATERIALS

Weatherboards, often just called boards, are traditionally wood-based, but there are many other materials available which give the look and feel of wooden boards, but with improved durability. Boards can be oriented in the traditional horizontal manner, but interlocking boards using tongue and groove or shiplap profiles are available that allow for vertical orientation for a more modern look. One interesting look is vertical boards spaced evenly on battens with fibre-cement sheet as a backing, visible through the gaps in the boards. Bear in mind that this look can be difficult to maintain as painting the boards is a slow process.

Wood weatherboards

Wood weatherboards are one of the most common forms of cladding on older homes as they are low cost and have a distinctive look. Wooden weatherboards come in a range of timber types, from softwoods such as pine through to native hardwoods and imported timbers. Unfortunately, a lot of softwood weatherboards do not originate in Australia, instead coming from the other side of the planet, from ecologically sensitive areas such as Russia’s boreal forests, so ask for sourcing information when looking at wooden boards (see bit.ly/2lttL0B). LOSP-treated radiata pine is available, but you may need to look around and ask questions. Salvaged boards are a good alternative to new timber.

Weatherboards generally need to be painted or varnished to be weather resistant. Boards will often rot if water gets under the finish—a common reason for weatherboard homes needing to be reclad. Some species of wood will weather naturally and are sometimes left uncoated or just oiled.

Board profiles vary and include traditional profiles such as round edge (bullnose), straight edge, shiplap and ‘VJ’ variations, which use a tongue and groove system. Finishes include dressed (smooth), pre-primed, raw sawn and rough sawn. Some boards are radially sawn, which means they are cut from the log in a different manner to conventional boards, maximising the wood cut from each log and thus requiring fewer trees.

The advantages of wood weatherboards include being a natural product (except for synthetic finishes) and arguably renewable. However, the source of the timber needs to be considered as there are still boards coming from native forests, both here in Australia and from overseas.

Another advantage with weatherboards is that they are easy to install for the DIYer. The average board is light enough for one person to lift into place with a bit of planning, so even a lone DIYer can reclad a wall or even an entire home, saving considerably on labour costs.

The primary disadvantage of wooden weatherboards is that they generally do need to be repainted regularly (every 10 to 15 years or so) and will degrade if neglected, so they are not the ideal choice if you are not into painting (or don’t want to keep paying for professional painters to do it).

Engineered timber boards

Engineered timber cladding can include materials such as plywood (covered earlier) and boards and battens. Engineered timber has been manufactured in some way, usually by bonding multiple pieces of timber together to form larger boards, sheets or profiles. It can be laminated in sheets, or finger-joined to form larger pieces, or use a combination of methods to produce the desired profile.

Engineered timber is generally worked and installed like regular timber and may come pre-finished or require finishing in some form. Advantages of engineered timber include consistency of the product (fewer knots, holes or cracks) and it often uses what would otherwise be scrap materials to make the finished product. Maintenance is similar to regular timber in that it will need to be regularly painted or varnished, unless it is pre-treated so that it can be left raw.

Composite boards

Composite boards have become quite popular in recent years. Most composite boards consist of a mix of cellulose fibre (usually from wood or other plant waste) and plastic, often from waste plastic. This means that the boards are almost entirely recycled content and prevent considerable volumes of waste materials going to landfill.

Fibre/plastic composites are usually extruded, so are available in a range of profiles. This manufacturing method allows for complex interlocking profiles, which makes for a robust, weatherproof installation. Many boards are available with surface textures to imitate the natural grain of wood. A good quality composite board looks just like quality, well-finished wood boards, even up close.

Composite boards come in a range of colours, with the colour being part of the board itself, so they never need painting or indeed any maintenance apart from the occasional clean. This makes them a prime choice for low-maintenance homes.

A variation on composite boards is the high-pressure laminated (HPL) board, where an outer finishing layer is pressure welded onto a composite baseboard, such as the Euro Selekta Clad boards. The end result is similar in appearance and usability to plastic-based composite boards.

Composite boards generally have similar flammability to wooden boards (a low BAL rating), but some composite materials have quite high BAL ratings; for example, the Euro Selekta Clad boards have a BAL 29 rating.

Modified wood boards

Modified wood boards are a form of composite board, but usually without the use of plastics. The most well-known example is Weathertex, which is 97% wood fibre and 3% wax. The wax gives the board weather and rot resistance and allows the boards to be used without further finishing, giving a low-maintenance result. However, the boards may still be painted or otherwise finished if desired. Weathertex boards are available in panels and shingles, and can be cut, drilled and screwed similar to plain wooden boards. The main downside with Weathertex is the comparatively higher cost compared to plain wood; however, hardwood boards can also be expensive, so the difference in price may be less than you expect.

Thermally modified wood is another product that has much greater rot and pest resistance than unmodified timber. It is created by a heat treatment process that ‘cooks’ some of the volatile compounds out of the wood and degrades the natural sugars in the timber so that fungus and rot can no longer live in the wood. The lifespan of thermally modified wood is vastly greater than untreated timber, and the treatment produces an equivalent rot/pest resistance to H3 treatment.

Acetylated timber (Accoya) is also a modified wood, but with a different treatment system called acetylation, which is much like using a vinegar to pickle the softwood (usually radiata pine). This modifies the wood so that pests like termites can no longer digest it, and mould is unable to gain a foothold due to the modified wood chemistry. Accoya is a very long-lived timber when exposed to the weather, even when unpainted, and has a rated lifespan of 50 years above ground. To meet BAL standards it has some specific installation requirements.

Fibre-cement planks

Fibre-cement sheet was covered earlier, but we should mention that this material is available in weatherboard-sized planks to provide a board-like finish. These boards usually require finishing, but some are designed to be left au naturel if desired. Generally, fibre-cement boards need a bit more effort to install than other boards as they are brittle if drilled too close to the end or edge. They are also heavy compared to other materials and require two people to install, so are less suitable to the DIYer unless you have a strong full-time helper.

Some fibre-cement products have been designed to address these issues. A good example is the Ubiq INEX weatherboards, which are made to be strong yet lightweight and are self-aligning (the board above has a notch that aligns it to the board below), with a three metre, 190mm wide (160mm coverage) board weighing just 12.5kg, allowing installation by one person.

Vinyl boards

Vinyl boards sound like something from the 1970s, but they are in fact alive and well in the 21st century. Vinyl weatherboards are PVC boards that work in conjunction with a moulded foam backing sheet which provides insulation and reduces curvature of the boards when installed. They are low cost and relatively low embodied energy and produce a finish which is essentially maintenance-free and long-lived: like composite boards, uPVC boards have the colour embedded in the board, so require no painting, with the only maintenance being occasional cleaning.

Their disadvantages include that they are, essentially, virgin PVC plastic and so contain no recycled content, and the PVC manufacturing process is one of the more toxic plastic-making processes. However, they are not plasticised, so at least don’t contain phthalates or other plasticisers, which are known endocrine disruptors and are listed as possible carcinogens.

Unplasticised PVC boards are made from the same material as uPVC window frames, so you may already have this material in your home. So far there is very little opportunity to recycle PVC plastic at end of life here in Australia and the same applies for the polystyrene foam backing sheet, which will most likely end up in landfill if the house is deconstructed a few decades down the track.

Another type of PVC weatherboard is similar in design to composite boards in that they use a much thicker self-supporting and rigid profile and no foam backing. These are not common, but one supplier in Australia is Clickonwall (clickonwall.com.au).

Aluminium boards

Similar to the thin foam-backed uPVC boards are aluminium boards. They use a similar system of foam backing and come in a range of colours, finishes and profiles. A typical example is Abbey Thermalboards, which come in both aluminium and uPVC. One advantage of aluminium boards over uPVC is that aluminium is truly recyclable, even here in Australia, whereas uPVC generally isn’t in most areas. However, aluminium boards are only recycled if they are easily separated from the foam backing; otherwise they will end up in landfill. One disadvantage is that aluminium boards will dent if they receive a heavy enough impact, making them look unsightly, unlike uPVC boards which will usually just spring back with minimal damage.

PVC boards combine thin PVC mouldings with foam backing to add rigidity and some insulation. They are very long lasting and can be fitted over existing old cladding, but recycling at end of life is yet to be resolved. Image: Progressive Foam
3. SHINGLES AND TILES
Shingles

Shingles are like tiles for your wall that overlap each other like weatherboards. Shingles are popular cladding in the USA, but not so much here in Australia.

Being small compared to boards and sheets, shingles are slow to install. They generally have to be affixed to sheet cladding, so actually require you to clad in sheet ply first, then add shingles over the top. This adds to the installation time and cost. However, some shingles, such as Weathertex shingles, come in sections of multiple shingles together, more like a short weatherboard that just happens to look like a bunch of shingles. Because they are made in lengths that are multiples of standard stud spacing widths, they don’t need sheet cladding underneath and can be affixed to framing just like weatherboards.

Shingles are usually made from wood or wood-composite materials, and so have the same requirements, advantages, disadvantages and maintenance requirements as boards and panels made from those same materials.

Another form of shingle is the shake. While shingles are machine-sawn both sides to provide a consistent profile, shakes are sawn on one side and hand or machine split on the other, for a more irregular finish than shingles.
While some shingles are made to consistent sizes, some are variable in size, which results in a more random pattern on the finished walls.

Tiles

Tiles, like shingles, are generally laid on top of sheet cladding or an existing flat surface such as brick or blockwork. Tile materials include ceramic and stone (such as slate, granite and quartz); one example is the stone tile cladding from Decor8 and stone panels from Décor Stone.

Stone cladding can come as panels, where a number of stone pieces are bonded to a backing, or as individual stone pieces which have a flat side and a ’natural’ side. Stone panels/tiles are generally glued into place and no further finishing is required. Corner profiles are usually available to complete the look, so stone can flow right up to the corners of each wall. Stone tiles come in a vast range of colours, patterns, styles and effects, including 3D, where some stones stand out from the rest, giving the finished wall a sense of solidity and depth.

A popular form of stone cladding is slate tiles. These can be regular shapes or random, and can be laid as tiles, or overlapped like shingles. An interesting example is on the cover of Sanctuary 47.

There are also a vast array of ceramic tiles available and most can be used as cladding, although larger tiles generally look better. Just remember that all tiles and stone cladding can be heavy (stone panels can be 100kg/m2 or more), so the substrate must be sound and robust.

Shingles can be individual wood shingles or easier-to-install and much more robust shingle ‘boards’, such as the Weathertex shingles shown here; made from wood dust and wax, these are weatherproof and pest resistant. Image: Weathertex
4. INSULATED CLADDING

While most cladding has minimal insulative effect, just the insulating ability of the material itself, some claddings are specifically designed to add a layer of insulation to a building. These usually take the form of insulative sheets, usually polystyrene foam or a similar foam board, with an outer layer of cladding to seal against weather and provide the final finish.

Rendered foam systems

Rendered foam systems consist of polystyrene foam sheet that is affixed over the existing cladding or directly to the wall framing (with a permeable sarking in between) over which a layer of render is applied. The render is usually reinforced for durability and the reinforcing can increase the fire rating, depending on the system selected.

If the foam is applied to existing cladding, some systems require battening to provide a ventilation space behind the foam, while others, such as Zego Z-Board, have convection channels in the rear face of foam sheets to eliminate the need for battens.

The foam sheets are usually fixed using long screws with special washers through the sheets into the frame and the render is applied over the foam sheets, including the screws. Render isn’t the only finish that can be used with these systems; it’s just as viable to simply cover the foam sheets with another cladding system such as Colorbond steel—in this case, the foam is insulation, nothing more.

The foam may be expanded or extruded polystyrene or other materials like phenolic foam, such as Kingspan’s Kooltherm K5 External Wall Board.

SIPs

Another form of insulated panel is the structural insulated panel, or SIP. While these are usually used to construct entire walls (they are structural components), they can also be used as cladding, being applied over framing or even old existing cladding. SIPs come in a range of types and thickness for different insulation levels. Many SIPs are foam sandwiched between two sheets of oriented strand board (OSB, a type of engineered wood similar to particle board, formed by adding adhesives and then compressing layers of wood strands (flakes) in specific orientations), which needs extra cladding. But some SIPs have a weatherproof outer skin such as aluminium and an inner skin of OSB, magnesium oxide board or other board made from mineral, metal or natural fibre.

Types of foam

While talking foam insulation, we should discuss the different types of foam and their environmental impact. The most common is EPS, or expanded polystyrene foam. Commonly called Styrofoam, this consists of thousands of small polystyrene beads expanded to form sheets or moulded shapes. It is cheap, but it is a significant environmental pollutant. Styrene takes hundreds of years to break down, and EPS foams tend to fragment and are very hard to contain on-site once sheets have been cut or otherwise modified.

A related foam is extruded polystyrene, or XPS. This is also polystyrene but is extruded as a single large piece of foam. It is stronger than EPS, doesn’t fragment to the same degree and has better insulation properties for a given thickness, but it is more expensive and suffers from the same environmental issues of being a long lifespan pollutant.

Phenolic resin (more accurately phenol formaldehyde resin) foams are rigid foams that perform better thermally than other foams such as polystyrene for the same thickness. They also produce lower fume levels in a fire and so should be considered if looking at foam panel cladding systems, although they are more expensive. The Kingspan Kooltherm range of panels are all made from closed-cell phenolic foam.

Phenolic foams do use formaldehyde in their manufacture, so are not without their environmental problems. However, one plus for them is that, unlike virtually all other plastic foams, phenol formaldehyde has been found to be degraded by the white rot fungus phanerochaete chrysosporium, making phenolic foams biodegradeable. While biodegradation is unlikely to happen easily in nature, particularly in landfill, this discovery (by University of Wisconsin back in 2006) means that phenolic resins could be degraded by this fungus in a controlled recycling system. However, we have not found any commercial systems using this process.

Polyisocyanurate (PIR) and polyurethane (PUR) are similar in manufacture and also better in thermal performance than polystyrene foams, although not as good as phenolic foams. However, they produce more toxic fumes in a fire than other foam types, including the dangerous gas hydrogen cyanide.

All these foams are generally non-recyclable here in Australia.

It is also important to understand the difference between open-cell and closed-cell foams. Closed-cell foams have tiny sealed bubbles inside of them which retain the original blowing agent (the gas used to expand the foam during manufacture). Because the cells are closed, air and moisture can’t travel through the foam, making them effective barriers against moisture. Open-cell foams have more irregular internal cells that overlap, creating internal channels through the foam. This allows air and moisture to travel through (and obviously into) the foam, reducing insulative ability over closed-cell foams. For add-on insulation in most structures you would specify a closed-cell foam with appropriate moisture elimination channels between the foam and inner sarking or structure.

Autoclaved aerated concrete (AAC)

Autoclaved aerated concrete (AAC) can also be used to add a level of insulation to an existing building. While often used as a structural wall material, it is also available in thinner panels suitable as external cladding. In this case it would normally be rendered for weathersealing.

cross-section of external thermal insulation
Rendered foam is usually laid over solid walls like block or concrete. Here you can see the various layers, including the foam, glue and the various render layers including reinforcing layer and final colour layer. Image: j_markow via iStock

Cladding finishes and maintenance

Some cladding options such as Colorbond steel have the finish built in, whereas others require additional finishing using coatings such as paints, varnishes or oils; these added finishes generally require more maintenance.

Finishes such as synthetic paints and varnishes can easily last 10 to 15 years before needing to be recoated, but this is dependent on the wall orientation—walls subject to greater weathering, such as west-facing walls, will need refinishing more often. If the finish is still in reasonably sound condition, a light sand to remove loose material may be all the preparation required, but more heavily degraded finishes may need complete sanding back, which will add greatly to the time and cost involved.

Renders are generally longer lasting than paints and varnishes, because they are not only much thicker, they have a high mineral content and are usually fibre reinforced, making them much more durable and less prone to penetration damage. Renders can last several decades if applied correctly, but repairing them can be more involved than simple repainting if repairs are required. The more a wall substrate moves, the more likely the render will crack and need repairs, so render durability can depend on the stability of the wall structure, both framing and footings.

Natural finishes such as oils need much more regular maintenance and some may need recoating every year or two. Re-oiling generally doesn’t require sanding first, which reduces the time it takes to do this task.

One interesting finishing system is ‘shou sugi ban’, the process of charring the surface of the wood. The charcoal acts as a barrier to weathering, greatly extending the lifespan of the timber, while adding an interesting effect. Be aware that the charcoal can be rubbed off over time, for example, if you have vegetation close to the house that brushes against it, leaving paler patches of uncharred timber.

Materials designed to provide a weathering finish generally need little or no maintenance. These include weathering steels such as Corten and certain species of timber. White cypress (Callitris glaucophylla) contains natural pest inhibitors and is quite long-lasting when exposed to the elements, as are various hardwoods such as ironbark, spotted gum, blackbutt and western red cedar. Unfortunately, white cypress is generally not responsibly sourced in Australia, but neither are many Australian hardwoods unless they are reclaimed or reused. As an alternative, Accoya wood (acetylated timber) is almost completely rot-proof.

Several types of materials have the finish built in and generally require no maintenance for the life of the product, potentially 30 to 50 years or longer. These include modified wood (such as Weathertex), composite and laminated products, pure plastics such as uPVC and various metals such as stainless steel.

Reclad or repair?

Homes with wooden weatherboards are usually prime candidates for recladding. The boards may have rotted due to water ingress, usually caused by failure of the paint or sealant to keep water out or damage from insects and other pests. Regardless of the cause of the damage, you need to assess whether to repair or reclad.

Small holes and minor rotting can be fixed. Holes can be filled and rotten sections can be cut or ground out, with new wood or filler used to fill the hole. Once all holes are filled, the cladding then needs to be sanded to remove the old paint or, if the paint is mostly sound, scrubbed down to remove any loose paint and then repainted.

Note that you need to be careful with old painted weatherboards that may have lead paint on them. If the paint is sound you should be able to paint over the top, but if the paint is loose or flaking it will need to be removed. This requires using a wet removal method such as paint stripper, wet scraping, wet sanding and low temperature heating (electric heat gun). Dry sanding can only be done using a HEPA filter sander. Regardless of the method used, a P2 particulate dust mask must be worn and drop sheets laid down so that all old paint can be collected and removed. For more information, see bit.ly/2Zeq9Tb.

Repairing and repainting old cladding can result in a quite satisfactory result, saving the cost of recladding, so it is well worth considering before ripping the old cladding off. It is also better from an environmental perspective, eliminating most of the materials used in a reclad.

If other tasks need to be performed while recladding, such as installing insulation or vermin mesh, then the cladding will need to come off. If the cladding is sound and you want to reuse it, then you will need to be careful when removing it. Weatherboards can be removed using a thin pry bar such as a Stanley 12” Wonder Bar or the smaller Crescent 7” flat pry bar. You can slip these under weatherboards and cut through the nails with a few taps of a hammer on the end of the bar, causing minimal damage to the existing boards. They are ideal for removing all sorts of boards, trims and what have you on home interiors and exteriors—every self-respecting DIYer should have one in their toolbox.

You can also avoid complete cladding replacement by just replacing the damaged boards or cladding. There are a number of online guides and videos on how to do this, such as youtu.be/HfdTRgpQTvg and the YouTube channel Living Big In A Tiny House.

Sometimes, cladding is not repairable due to extensive degradation or damage from external causes such as bushfire. Complete cladding replacement is a great opportunity to do any insulation upgrades while the cladding is off, as well as changing the look of your home. In simple terms, the old cladding is removed, insulation and sarking etc is repaired or upgraded, and new cladding and associated trims are installed, sealed and painted or rendered if required. The whole process can take from a couple of days for an experienced cladding company to several weeks for a lone DIYer; don’t underestimate the amount of time and effort required. For DIYers, it is best to do a single wall section at a time. This lets you learn as you go and see the results of the upgrade almost immediately.

Not all recladding requires that the old cladding be removed. It is often possible to simply reclad over the top of existing cladding, so long as the appropriate cavity spacing is provided if required. This usually involves vertical battens being affixed to the existing cladding, with the new cladding installed onto the battens. However, this sort of work is not for the inexperienced DIYer and help should be sought if you have any doubts or questions about the recladding process. After all, cladding, like roofing, keeps the weather out of the rest of the building envelope and so it is of high importance that it be installed correctly to avoid problems down the line.

 

Acknowledgements:

Thank you to Raphie Kruse, an environmental design consultant at Paul Haar Architecture, for her review of this article.

Resources:

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