Often a barrier to switching to light-weight steel framing is the habit of ‘thinking timber’. As Bruce points out, ‘With no first-hand experience of steel framing, it is easy to prefer to go with what you know.’
Like any material choice, the advantages and disadvantages need to be assessed. Design flexibility aside, Bruce went with steel rather than timber framing primarily because of concerns around leaky homes. Steel does not absorb moisture so it won’t warp or twist. This makes it reliably stable and eliminates some maintenance issues associated with timber − like cracked linings and sticking doors.
| Timber framing | Steel framing | |
|---|---|---|
| Design | Lower strength-to-weight ratio, requires shorter spans and more framing. | Higher ratio allowing longer spans and less framing. |
| Floors may be more lively. | ||
| Building Code | Acceptable Solution. | Specific design. |
| Construction | Builders are familiar with timber construction. | Light-weight, easy to handle. |
| Requires standard carpentry tools. | Requires specialist steel-fixing tools. | |
| Design easily modified. | Precut lengths, design less adaptable. | |
| Cladding/lining can be nailed or screwed. | Cladding/lining must be screw fixed. | |
| Services holes must be drilled. | Services holes prepunched and require grommets to protect pipes and wiring. | |
| Handling not critical. | Correct handling essential to avoid frame damage. | |
| Thermal break | Not required. | Required. |
| Frame stability | May warp/twist. | Remains straight and true. |
| Moisture | Fungal attack and timber decay if remains wet. Higher levels of treatment. | Coating protects from corrosion. |
| Fire | Combustible. | Non-combustible. |
| Retains structural strength in unburnt timber. | Loses structural strength in a fire. | |
| Sustainability | Can reuse. Recycle untreated only. | Can reuse and recycle. |
| CO2 emissions | Carbon sink during tree growth. | Production of 1 tonne of steel emits approximately 2 tonnes of CO2. |
| Embodied energy | 2.8–9.5 MJ/kg (air/kiln dried and rough sawn/dressed). | 10.1–35 MJ/kg (recycled/new steel) but only ⅓ the mass of timber is required. |
| Health and safety | Contains preservatives with varying levels of toxicity, may gas off. | Non-toxic, may need earthing. |
| Other | Similar cost for framing. | Similar cost for framing. |
| Renovations are simpler. | Straighter walls, square corners. |
There is another benefit on site as well. Bruce’s new Orewa home was built over winter. ‘With steel, you can just put the frame up and get on with it, regardless of the weather.’
Smooth transition on site
Both designer and builder agreed that it was a smooth transition even with the first-time learning curve. Colin Green of Colin Green Building explains, ‘Like with anything, the more you use a product, the quicker you become at using it. It’s not a difficult difference. You just put aside your nailing gun and skilly and bring out the tin snips and screws and drill. I enjoyed working with the steel frame.’
The steel frames were delivered to the site prefabricated and with service holes prepunched. ‘Once lifted into place, they are simply screwed, no welding required,’ says Colin. ‘Steel walls are straight and never deviate.’
Simple construction
Colin shared some examples of the simplicity of steel construction. ‘The handrail was easy because we constructed the framework, and the capping for the top was supplied. This made it rigid, and no angle brackets at the base were required to hold it solid. Also, there was no ply construction needed to brace the chimney area. We put on cavity battens and clad them with cedar weatherboards.’
If builders regularly build with timber, that familiarity makes it feel easy. But Bruce says, ‘There are many grades of timber and additional preservative chemicals associated with timber, so you have to be careful in terms of where you can use it safely. With steel, you can use it anywhere.’
This house wasn’t priced in timber framing and generally the choice of framing will be price neutral.
As you would expect for the first time around, both designer and builder took a while to get into the flow of using steel rather than timber, as did subcontractors. In the end however, the experience proved to be positive.