54 BUILD February/March 2009 STEEL RESIDENTIAL STEEL FRAMING Although steel framing has a tiny market share in the local housing industry, the National Association of Steel-framed Housing (NASH) believe it’s popularity will grow as its benefits become better known. By Carl Davies, General Manager, National Association of Steel-framed Housing Inc. T he light gauge steel-framing industry is well established in New Zealand as a viable option for the structural framing of dwellings. Increasingly, it is also being used in other low-rise commercial and community buildings. Steel house frames were first used in New Zealand in the late 1960s, and the first steel framer, Stuart Thompson, started operation in Wellington in 1970. Steel framing has gained popularity in many European countries, America, Japan, South Africa and Australia. In Australia, steel framing captures around 12% of the market nationally and over 30% in some regional areas. Here, it is a more modest 2.5% of the housing market, but this is growing, and the industry’s aim is to achieve 10% by 2011. Durable Steel frames have proven to be durable since their introduction into New Zealand in the 1960s, as long as good building practices are follow- ed. Good practices include matching cladding fasteners to the external environment (unlike timber, the external environment that the head of the fastener is exposed to is critical), quality on- site workmanship, design of cladding and framing around openings to stop ingress of moisture, and thermal breaks to keep the studs above the dewpoint in winter and obtain the required thermal performance. New Zealand Steel provides a 50-year durability statement on steel for framing, provided good building practice is followed. Steel frames are manufactured and assembled to tight tolerances, and this permits the installation of the frame to similar tolerances. Steel has the advantages that it is does not warp or creep with time and does not absorb moisture. It does not rot, support the growth of mould or rust when good weathertightness principles are applied to the cladding design and installation. Safety and health pluses Steel frames provide occupants with extra pro- tection from lightning, as energy is conducted straight to ground and not released destructively within the frame. Steel frames resist fire and may deform but not burn under high temperatures. Steel framing does not release any gaseous products or support growth of mould. This has benefits for occupants with respiratory problems and has led to the Asthma and Respiratory Foundation of New Zealand recognising its benefits for asthma and allergy sufferers in their Sensitive Choice programme. Flexibility and speedy construction Steel framing’s strength and stiffness allows long span trusses that can be used to design large open rooms and to relocate non-load bearing walls as the household needs change. Light-weight non-load bearing steel-framed walls can be as easily, quickly and cleanly changed as timber walls, to suit a new house configuration. Due to its high strength-to-weight ratio, steel provides lighter structural members that speed up construction. For an average house, a crew of two to three can typically erect the steel framing in a couple of days. For some building designs, the strength and rigidity of steel allows the steel trusses to be assembled on the slab and the steel roof sheeting attached to the roof. The whole roof assembly can then be lifted on to the steel walls. Having many assembly operations performed at slab level makes this method faster and safer, but it does not suit all designs. Space is needed to place the roof while sufficient walls are erected to take the roof load. Veneer construction allows great flexibility in planning and does not rely on the speed of bricklayers for progress. This takes bricklaying off the critical path in the construction of the house. Service holes are provided in the stud walls, which allow for fast installation of plumbing and electrical services. However, incorporating thermal breaks needs to be allowed for. Dimensional stability Steel studs do not absorb moisture and are dimensionally stable. This aids accuracy of con- struction, quality of finish, avoidance of cracking and popping of nails. Construction can proceed Residential steel framing. (All photos courtesy of FrameCad.)