Residential steel framing

This Issue This is a part of the Steel feature

By - , Build 110

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.

Residential steel framing. (All photos courtesy of FrameCad.)
Residential steel framing. (All photos courtesy of FrameCad.)

The 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 followed. 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 protection 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 construction, quality of finish, avoidance of cracking and popping of nails. Construction can proceed in damp and cold conditions, and any surface moisture will evaporate once the building is weathertight. This removes the need to wait for moisture contents to fall to acceptable levels for placement of cavity insulation and wall linings.

Environmental advantages

Environmental issues are receiving increasing attention by designers, but comparing benefits of different systems can be difficult. NASH advocates the lifecycle analysis of the building as the best current method to compare systems. This includes the energy required to manufacture the materials, to construct, to operate and, finally, to demolish the building. The operational energy in housing has been found to dominate the lifecycle analysis and the embodied energy within the materials has a negligible influence on the total outcome.

Some more environmental advantages for steel framing include:

  • the building can be easily reconfigured to suit changing needs
  • steel framing can be reused when the building is demolished
  • steel is 100% recyclable
  • wastage levels in a steel fabrication plant with its own roll formers are typically less than 1%.

Cost

When comparing the costs of construction, all relevant cost components should be considered to obtain a true picture. Steel frame offers benefits that are hard to value, such as flatter walls, square corners, no problems with nail popping and provision of service holes.

Depending on the design and local market conditions, steel frames can cost no more than timber, and at least one major housing company currently offers a saving on steel over timber-framed homes.

Damage and fastener performance

Steel framing is susceptible to local frame damage. The thin-walled steel stud cross sections are less robust than timber studs and, therefore, prone to permanent buckling if handled incorrectly during transportation and erection.

Fastener behaviour and capacity is quite different from that in timber studs because of the thin-walled nature of steel studs. If failures occur, it is usually within the connected plies or a combined ply/fastener failure, rather than a fastener failure. There are established procedures for determining fastener capacity into steel studs, and these must be followed.

Ensuring Code compliance

Currently, steel requires more engineering design and documentation than timber framing, principally reflecting the new nature of the system. Technical documentation being developed by NASH, and increasing use of the system, is expected to overcome this in the medium term.

Builders and subtrades are less familiar with steel framing than with timber framing. This is being addressed through experience, education and training.

NASH is working with the Department of Building and Housing on developing its own NASH standard – residential and low-rise steel framing to assist compliance with the Building Code. A handbook for architects and designers in using light steel framing will follow.

Education and training

Education and training at both the professional and trade level are important. Carpenters have traditionally constructed timber frames. As the skills for erecting steel and timber framing are similar, it is logical that they also erect steel frames. NASH has been working with the Building and Construction Industry Training Organisation (BCITO) to ensure that future tradespeople are trained to confidently work with steel framing.

Market growth expected

Steel framing initially found a ready market with owner-builders, who were generally well informed about product performance and prepared to accept slightly higher costs for the framing and trade services. As the industry grew, progressive builders were targeted to use steel framing in all or part of their houses, and some of these now make their own steel frames.

Today, steel framing is often targeted at owners who want a quality product. NASH predicts steady market share growth over the next couple of years despite more aggressive competition from other sectors.

For more

See www.nashnz.org.nz.

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Articles are correct at the time of publication but may have since become outdated.

Residential steel framing. (All photos courtesy of FrameCad.)
Residential steel framing. (All photos courtesy of FrameCad.)

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