Composite benefits: When are SIPs the right choice?

As cost-effective, resource-efficient and sustainable builds increasingly become a priority, structural insulated panels (SIPs) provide a strong, efficient and lightweight prefabricated alternative for walls, roofs, and floors. The high performance composite building material is a load-bearing structural system consisting of an expanded polystyrene (EPS) insulating foam core sandwiched between two outer engineered skins, typically oriented strand board (OSB), but which may also be magnesium oxide, plywood, sheet metal or fibre cement.

Offering material and structural efficiencies, SIPs are touted for achieving savings in time and money, and creating an airtight and energy-efficient result. But do they live up to the hype?

Costs and construction

While SIPs may have a higher upfront cost than traditional framing, the prefabricated system effectively removes the need for multiple building materials and allows for reduced onsite construction times. Erecting a building in less time should reduce labour costs, but currently there are limited contractors experienced in using SIPs, which can consequently affect the pricing.

“From our experience it is a viable construction technique for any new project, but the lack of experience in the building trades is currently holding it back,” says architect Kieron Gait. He used SIPs for a residential extension and says quoted savings varied from $0 to $20,000 because of contractors’ lack of familiarity with the product. Using SIPs did, however, ultimately save up to four weeks in expected construction time.
Max Capocaccio of MC Architecture Studio has used SIPs in four completed houses to date and says cost savings are attainable, although not always achieved, and stresses that it is essential to have a team familiar with the product. “We have learnt that it is paramount the team works well together from design through to construction. If well coordinated, construction with SIPs can be very effective in time and cost management,” Max says. He adds that a main issue is to reduce weather exposure during construction as moisture can cause damage.

This warehouse-style home in Christchurch, by MC Architecture Studio, uses SIPs for the walls in combination with materials reclaimed from the factory building that existed on the site prior to the recent earthquake. Image: Mick Stephenson

This warehouse-style home in Christchurch, by MC Architecture Studio, uses SIPs for the walls in combination with materials reclaimed from the factory building that existed on the site prior to the recent earthquake. Image: Mick Stephenson

Architecture and design

SIPs are modular in nature and while they can be fabricated to fit a vast range of building designs, it is best to work with the standardised system to take advantage of its efficiencies.

Leaving the SIPs exposed can contribute to savings as it eliminates trades such as painting, however the aesthetic of the cladding may be an influencing factor. Architect David Barr created a warm, textural space using OSB SIPs for an extension in which the client wanted to explore its materiality. “If the material is to be left raw, then it is important to ensure the building team understands the intent of the final finish, so that it is finished neatly and treated with care,” he advises. In contrast, the SIPs panels are covered in Max’s Kingswood House, providing a white backdrop to the exposed timber floor, ceiling and roof trusses that imbue the space with warmth and texture.

This project by Gillian Manning Architecture (near Bacchus Marsh, Victoria, and shown here during construction) uses SIPs comprising two pieces of oriented strand board (OSB) with polystyrene insulation between. The SIPs were treated as a nominated subcontract and the house was tendered traditionally, though this process took a little longer than normal due to the apprehension for building trades for using the material. Mark Lane Quality Builders was receptive to the job, and found they increased the speed of construction from slab and subfloor to ‘lock up’. Image: Hilary Bradford

This project by Gillian Manning Architecture (near Bacchus Marsh, Victoria, and shown here during construction) uses SIPs comprising two pieces of oriented strand board (OSB) with polystyrene insulation between. The SIPs were treated as a nominated subcontract and the house was tendered traditionally, though this process took a little longer than normal due to the apprehension for building trades for using the material. Mark Lane Quality Builders was receptive to the job, and found they increased the speed of construction from slab and subfloor to ‘lock up’. Image: Hilary Bradford

Sustainability and energy efficiency

The sustainability and energy efficiency benefits of SIPs are often key factors for using them. Prefabrication means reduced waste, and the achievement of a high level of airtightness. “The reduction of thermal bridging and high R value are the main aspects taken into account,” Max says; both contribute to a decrease in heat transfer.

Max, David and Kieron express positive client reports about the thermal performance of SIPs. As their homes stay warmer in winter and cooler in summer, artificial heating is reduced, and there is no need for air conditioning. “Our clients’ feedback is that it makes them feel protected,” Kieron says. Questions remain around disposal at end of life, however.

MC Architecture Studio in New Zealand has used SIPs for four projects to date, including Black Door house where they are used for the walls and roof. Image: Mick Stephenson

MC Architecture Studio in New Zealand has used SIPs for four projects to date, including Black Door house where they are used for the walls and roof. Image: Mick Stephenson

Health and safety

SIPs pass fire endurance tests due to their construction as the skins protect the core for a period, but it is advisable to speak to manufacturers regarding product-specific BAL compliance. Fire-resistant plasterboard can be used to improve on the required fire rating.

SIPs that use EPS are a non-toxic building material in that the skins contain no formaldehyde. The airtightness that can be more easily achieved with SIPs can also reduce the need for artificial heating and cooling and contribute to improved indoor air quality – no more dust! Buildings that are airtight may need good mechanical ventilation and humidity control, however, especially if materials with impermeable skins are used.

So, are SIPs the right choice for your home?

It takes time for new materials to be embraced by design and building industries, and for builders to gain experience with products and construction methods. While SIPs are becoming more commonly used as a construction material, finding a builder who is comfortable using SIPs will help you maximise their material, structural and cost efficiencies.


 

Rebecca Gross is a freelance writer, researcher and design historian. She has a master’s degree from Parsons School of Design and is interested in understanding culture through the lens of architecture and design.

Feature image: Architect David Barr says the oriented strand board clad in SIPs created a warm, textural space for this addition to a Federation-era house in Perth. Image: Nic Montagu

Purr-fect design

Cats as pets: it’s a divisive subject. But whether you love them or loathe them, cats are here to stay. As an animal lover and cat owner, I adore cats, but as a wildlife veterinarian frequently dealing with the terrible injuries they inflict on our native animals, I’m conflicted.

Cats have contributed to the extinction of dozens of Australia’s native mammals and birds, and are listed as a key threat to many currently endangered animals. Due to these devastating effects, there have been calls for pet cats to be permanently confined to their owner’s property. Cat owners might be surprised to find that their smooch puss is a highly effective killer: according to research in Canberra that followed cats for 12 months, 70 per cent of cats were bringing home prey monthly, and 6 per cent of cats were bringing home prey weekly. And that’s only the prey they decided to share!

Sunset-to-sunrise cat curfews, enacted decades ago by some local governments, do not reduce hunting of prey species active during the day, such as birds and reptiles, so an increasing number of local councils around Australia are passing orders requiring owners to permanently confine their cats, particularly in new suburbs or those adjacent to bush habitats.

But it’s not just about the wildlife. As a veterinarian I see the whole spectrum of injuries and disease occurring as a result of cats roaming. Cats fight each other, causing serious injuries and spreading Feline Immunodeficiency Virus. They are very frequently injured severely or killed on the roads. Dogs will kill or severely injure cats entering their yards. Cats may stray and become lost. Cats can cause neighbourhood disputes. And of course there is toxoplasmosis, a disease caught from the faeces of cats that hunt or are fed raw meat; it’s dangerous to an unborn baby if contracted by pregnant women, and frequently lethal to our native mammals.

There are many good reasons to confine cats; happily there are a number of ways to do this that are effective and aesthetically pleasing.

Confinement indoors

Some owners will confine their cats inside the house, simply by closing the doors. Although this is a cheap and valid option, it does require constant vigilance, and training of visitors. An important aspect of house confinement is keeping the cat enriched to reduce boredom and lifestyle diseases such as obesity, diabetes and urinary tract disease. Options include active play, a variety of rotating toys including those that make a cat work for their food, cat trees and basking points, litter trays (one per cat plus one to reduce conflict), tall scratching posts, and views out of windows.

Some owners have taken these ideas further by modifying their house to accommodate their feline friends. Cats use vertical space, so clearing off shelves with easy access points, or even building cat walkways or tunnels along walls or across ceilings can significantly improve your cat’s day, are a lot of fun, and can be great to look at. Some cats can be taught to enjoy walking outside your property on harnesses, although they tend to walk you, rather than the other way around. Cats should never be left harnessed without supervision.

Wowowa’s Casa de Gatos ‘house of cats’ project is a renovation to a tiny worker’s cottage in North Fitzroy to make space for a travel-loving couple and their four fur babies: two dogs and two cats. For the cats, a climbable wall surface was installed with vertical spaces for the cats to roam without needing to go outside. Images above and feature image: Martina Gemmola

Wowowa’s Casa de Gatos ‘house of cats’ project is a renovation to a tiny worker’s cottage in North Fitzroy to make space for a travel-loving couple and their four fur babies: two dogs and two cats. For the cats, a climbable wall surface was installed with vertical spaces for the cats to roam without needing to go outside. Images above and feature image: Martina Gemmola

Cat runs

You will have a happier cat if they can use some outdoor space. One option is a roofed cat run or enclosure, which can be made from metal mesh or netting.

Galvanised steel mesh: Mesh cat runs can be stand-alone cages – attractive for cat owners who rent – or built in permanently to your property. They tend to be more expensive than other solutions, but some are available as DIY kits, which can reduce costs. If built in, they are best permanently connected to your house by a tunnel and cat door, allowing the cat to choose when to access the run; this is particularly important during extreme weather, or for anxious animals. Unless you invest in an energy-rated pet door, there is a minor consideration that a connecting cat door can be draughty and may be frequently opened by your cat, resulting in poor thermal performance of the room it is connected to. The ideal place to situate a cat door is away from the main heated area. Cat doors can be installed in most walls and in single-glazed windows made of safety glass.

Netting: Traditionally cat runs are made of galvanised mesh, however a number of companies offer netting as an alternative. The choice of netting is important. Nets originally made for fishing or sports are not suitable, as these are designed to sag, which can require re-tensioning over time, or could result in the cat becoming caught and entangled if it attempts to climb the sagging netting. Pre-stretched heat-set, UV-stabilised netting designed specifically for cats is preferable, and will last longer. Netting may be designed to be low visibility, reducing the visual impact of your enclosure. Most netting enclosures are custom designed to suit your property, making maximum use of the space you have available.

Furnishings: Remembering that cats enjoy vertical space, you can significantly increase the useable size of your enclosure by providing perches, walkways and cat climbing furniture within it.

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Panache (Burmese) and Mia (Abyssinian) love catching the sun, chasing butterflies and 'bird watching'. They used to be kept in at night only, but due to the risk of cars were grounded for life. “At first the cats looked for a way out of their netted enclosure but soon accepted the new normal,” says owner Michael. The enclosure surrounds the laundry door and clothesline so it's still easy to hang the washing, with the cats keeping company.

Panache (Burmese) and Mia (Abyssinian) love catching the sun, chasing butterflies and ‘bird watching’. They used to be kept in at night only, but due to the risk of cars were grounded for life. “At first the cats looked for a way out of their netted enclosure but soon accepted the new normal,” says owner Michael. The enclosure surrounds the laundry door and clothesline so it’s still easy to hang the washing, with the cats keeping company.

Cat fencing

Confining your cat to your backyard using fencing has a number of advantages. It may be cheaper to install cat-proof fencing than an enclosure, and, as you continue to share the space with your cat, allows maximum use of the backyard for both you and your pet. Although good fencing will prevent neighbours’ cats from entering your backyard, your cat can still hunt any prey species that come in.

Before starting you will need to seal off any gaps in or underneath the fence, and trim back trees and shrubs or provide tree collars to prevent climbing. You will also need to remove or discourage access to any launching places, such as garbage bins or planters. Fencing alone may be adequate, if it is tall enough, made of metal to reduce grip, and without horizontal rails (for example Good Neighbour fencing). Gates can be a weak point, and some options outlined below include special gate kits to reduce escape over gates. If fencing is not enough, or difficult to alter, you may need to consider fence ‘additions’ to reduce escapes.

There are a number of DIY guides for building cat fencing available online from councils and welfare organisations. It’s a good idea to follow these guides to minimise risk to your cat.

Floppy fencing: ‘Floppy fencing’ your backyard involves using angled brackets or angled PVC pipe attached at regular intervals inside your fence, with netting or wire mesh running between them to create a barrier. This can be a relatively low cost DIY project.

Electric fencing: Cat electric fencing – such as the Pingg-String from Suregard and SmartCats StayHome cat fence – are a low-visibility, relatively low-cost option for cat confinement. They are fixed to the top of fences, or angled just inside your own fence using brackets, and can be attached to outdoor power points or use solar panels. The electric fence must be specific for cats, so that the electric shock is appropriate for their body size; livestock fences are not appropriate.

However, the RSPCA discourages the use of electric fences. In order to learn to avoid them, the cat must receive at least one shock. In addition, cats generally do not respond well to punishment, often increasing anxiety or redirecting aggression to other animals or people when they are frightened. They may also simply ‘run through’ the fence if terrified.

My personal experience with a cat electric fence has been positive, particularly when renting. Ours had a low visual impact and few attachment points, making it easy to move between rental properties and acceptable to our landlords, and it was very cost effective. It did require some ongoing maintenance when wires shorted, but with proper tensioning this would be less of a problem.

Cat containment paddles: Cat containment paddles such as those from Oscillot provide a good alternative to other fencing modifications for high fences (minimum 1.8 metres). As a cat jumps it reaches to the top of the fence with its forepaws, contacting the paddle. The paddle spins and the cat loses its grip, dropping back into the yard. It can be installed yourself, and depending on the yard size, can be economic. This fencing is approved by the Animal Welfare League of Australia.

Images: Oscillot

Images: Oscillot

The way forward?

Without a doubt cats make delightful pets, but the carnage wrought by cats, feral and domestic, has reduced biodiversity in our urban, periurban, rural and wilderness habitats, and roaming is a dangerous lifestyle for cats. With so many options for cat confinement available – many cost effective, cosmetic and discreet – as a wildlife veterinarian and a cat lover, it is my fervent wish that more cat owners embrace responsible cat ownership by confining their cat to their property.


 

More info:
www.awlqld.com.au/wp-content/uploads/2011/07/cat-safe-booklet.pdf