Date:30 April 2008
Tough, durable and earthquake-proof, the light steel-frame house is becoming increasingly popular in South Africa. Bring on the tremors…
Remember the story about the Three Little Pigs, and the third and final house – constructed from reassuringly solid bricks – that stood firm against everything the Big Bad Wolf threw at it? Well, that more or less sums up the mindset of most South African home builders. If you want your house to last, they say, you can’t go wrong with bricks. Quite right, too – but recent developments suggest there’s another way.
Light steel-frame homes might be relatively new to South Africa, but their ability to withstand the worst Nature has to offer is already legendary. The fact that they’re highly effective in hurricane- and earthquake-prone regions may not be especially relevant to the local building industry, but it’s reassuring news for anyone who might have doubts about their toughness or durability.
In fact, there’s a lot going for today’s steel-framed house: its design is highly adaptable, it accepts any cladding, and it requires about one-third less time to construct than a conventional brick building. If you’re about to embark on a home-building exercise, now’s the time to do some homework, examine the options and ask a few pertinent – and impertinent – questions.
Everyone has a home-building horror story. Although details may vary, it usually features complaints about unreliable builders, sites that resemble war zones, schedules of laughable inaccuracy, and budgets better suited to oil sheiks. So you’ve changed your mind about the location of a window or the angle of a staircase? Well, you’d better be on very good terms with your bank manager.
According to industry insiders, light steel-frame (LSF) homes are fabricated with far more accuracy than can be achieved with bricks and mortar, so many of the hassles traditionally associated with home building are eliminated. Clever design software allows you to implement changes up to the last minute, automatically recalculating the measurements to accommodate your wishes.
This means you can reconfigure the building or introduce additional features – perhaps an extra pair of patio doors – without boosting your builder’s blood pressure, and perhaps more significant, without breaking the bank. Against that, once they hit the start button on the computer-driven steel roll former, you’re committed.
Only five workers are required to erect and clad the frame, which brings down labour costs – generally a big-ticket item on the budget – quite dramatically. The surrounding area remains largely unmolested, which should make your neighbours happy. And it all happens very quickly: you can expect construction time to be cut by about one-third. Oh, and it all fits.
The team at Durban-based Mystic Blue Construction clearly have confidence in their products and methods. Not content with building a single showcase home, they’ve opted for a distinctly upmarket development on Amanzimtoti’s scenic coastline, calling it Antigua Estate. Comprising 40 sea-facing units, the development cashes in on the area’s natural beauty with six different styles of home that range in size from 119 to 214 m².
Mark Geyser, MB Construction’s engineer and the “man who puts the Meccano set together”, is upbeat about their progress, and expects to have the first 10 units completed within six months: “Our show house is receiving rave reviews… we’re over the moon. If we could sell all 40 units and raise enough capital, we could finish the entire development in just nine months – an impossible goal if we were building with bricks and mortar. At present, we’re using five guys per house, and they’re taking about two months to do the job. If we put 15 guys on site, each unit would take just two weeks to complete.”
All the frames are manufactured from high-tensile galvanized steel sheeting. First, the building plans are captured by steel-framing computer software. Next, the structural design is automatically configured and the exact detail for each individual section is determined – right down to where holes need to be punched for electrical conduits and plumbing.
Data is then sent to a computer-controlled rollformer, which profiles, cuts to length and punches each piece. As the sections of profiled steel are spat out of the rollformer, they are assembled into wall panels, roof trusses and floor joists.
All bolts, rivets and self-tapping screws used are specifically engineered to ensure structural integrity. Finally, the entire frame is dispatched to the construction site in kit form. From start to finish, with a full construction team in place, the frame can go from design phase to completion in about five days.
Once erected, the frame is clad externally with Oriented Strand Board (OSB), a structural panel engineered for uniformity and strength (it’s manufactured from fast-growing trees that are processed into precise strands). The strands are mixed with wax and resins, formed into mats (oriented in cross-directional layers for increased strength), then compressed at high temperatures to form panels. Benefits include moisture and impact resistance as well as excellent thermal and acoustic isolation properties.
The entire structure is then wrapped in a polypropylene membrane, which allows air movement but keeps moisture out. Finally, fibre-cement board is placed over the membrane to make up the external cladding, which can be plastered in the conventional manner if required. If fibre-cement board doesn’t work for you, no problem: virtually any cladding can be used, from single brick wall to wood.
Internal walls are clad with 15 mm structural gypsum board, a material with impressively high impact-resistant properties as well as a one and a half hour fire rating. Insulation is then inserted into the wall cavities, reportedly achieving better thermal and acoustic performance than brick walls and making the structure extremely energy efficient.
When it comes to installing wiring and plumbing, nothing could be easier. Because the frame has already been prepared, the plumbers and electricians can get to work as soon as everything has been bolted together. Plus, the structural accuracy of the frame means that installers don’t have to waste time fiddling with cupboards to get them flush and level.
One caveat, though: for everything to work out right, the foundation measurements need to be perfect. Explains Steve Cullender of Scottsdale Construction Systems SA: “When laying bricks, there’s not much need for accuracy; to get everything level, all you need do is add some extra mortar. But because the steel frames are manufactured to tolerances of just half a millimetre, the measurements need to be exact.”
He should know: his New Zealand-based parent company, Scottsdale International, has been in the business for years. It designs the software, develops the rollforming machinery and provides the industry with all the tools necessary to ensure the success of projects in 21 different countries.
Not surprisingly, Cullender is a strong advocate of LSF structures. As he points out: “You cannot build in brick and mortar in areas where there is seismic activity, because if a quake happened, people would die. That’s why these places have opted for timber frames.”
In countries that are familiar with framed structures, the advantages of steel over wood are grasped immediately. But here at home, says Cullender, the going has been slow: “We’re talking first-world building technology in a place that only trusts bricks and mortar.”
However, that seems set to change, and growing numbers of home builders are embracing the concept of steel-frame designs.
The weight difference between LSF and brick homes is astonishing. Cullender elaborates: “One square metre of double brick wall weighs 500 kg, whereas a square metre of our walling tips the scale at just 50 kg.” This means the foundations can be lighter, and hence cost less.
Two people can easily handle entire wall-panels, and vertical extensions to existing homes with single foundations is a non-issue. Says Cullender: “If you have a small brick home and want to convert it to a double-storey, you simply take off your roof, add the walls, and replace the roof.” More modest extensions are a piece of cake.
The weight difference – about 25 tons for a 100 m² brick house versus steel’s 2,5 tons – also translates into significant savings in transportation costs.
If you're of the opinion that lightweight means flimsy, think again. Many of the homes left standing (with roofs intact) after Hurricane Katrina hit the southern United States were light steel-frame homes. Aggressive marine and industrial environmental tests have determined that the galvanised steel frame inside the building envelope should resist atmospheric corrosion for several hundred years.
It gets better. The structure can handle some foundation movement without cracking. Its frame won't warp, it's impervious to pests, and it cannot burn or rot. And to keep everything in environmentally friendly perspective, here's an interesting snippet: to provide the material needed to frame your new 200 m2 home, you'd need to come up with six scrapped cars. Sounds like a good deal to us.
Check out Mystic Blue Construction's Antigua Estate development at www. antiguaestate.co.za For more information, contact Scottsdale Construction Systems SA's Alison Snowdon on 021-790 6662 or visit www.scottsdale.co.nz