A cladding buyers guide
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.