Lightweight material – heavyweight protection

Our trans-Tasman neighbours often refer to us as the Shaky Isles, largely because of where we are. 

New Zealand lives in an interesting seismic neighbourhood, on the boundary between the Australian Plate and the Pacific Plate. Along these plates are many faults including some of the higher profile ones like the Alpine and Wellington Faults. 

Earthquakes happen when blocks of rock move upwards and sideways. The smaller ones go unnoticed, but the larger events can, and do, cause enormous damage to people and property. 

Humankind is yet to develop the ultimate earthquake-friendly structure capable of standing up to anything. But the ‘code’ certainly has been cracked in terms of creating materials that can withstand sizeable shocks, and which limit damage in the event they do collapse.

Shockingly clear

In the wake of the Christchurch Earthquakes, one of the clear messages coming from experts is the strong recommendation to use lightweight metal roofing over heavy tiled options. 

The science is quite specific. The Canterbury Earthquakes: scientific answers to critical questions (2011), a report compiled by scientists and engineers from a range of disciplines, simply states:

“When building, use ‘earthquake friendly’ materials… Remove heavy roofs like concrete tiles and replace them with lightweight materials such as steel.”

Roofs can also act like a safety net. Christopher Kay, of COLORSTEEL®, says: 

“Lightweight COLORSTEEL® roofing has proven to be a strong performer in the recent seismic activity – in most cases where a brick chimney collapsed onto a COLORSTEEL® roof it went no further. The combination of chimney and tile roof collapses coming together can cause enormous damage to anyone, or anything, underneath. Metal roofs are about 1/7^th the weight of concrete tiles. There’s no reason to take risks especially when lightweight but durable options are widely available.” 

This view is reinforced by experts in the field. Experienced in post-disaster engineering reporting, well-known structural engineer Wayne Brown was one of a team who assessed damage to Canterbury homes following the 22^nd February 2011 earthquake.

His inspections revealed extensive damage was caused to houses by chimneys falling through heavy tiled roofs, or by the tiles coming loose and falling. Metal roofing, on the other hand, generally did not collapse under falling chimneys and was able to withstand the quakes themselves.

He finished by suggesting a ban of both roof tiles and chimney bricks, and proposed using iron roofs and steel chimney flues instead.

Supported by science

Another report, compiled by Professor Andy Buchanan and Michael Newcombe at the University of Canterbury, noted that metal roofs were better able to withstand the impact of falling chimneys 

What’s more, the report observed how the weight of a structure affected homes’ performances during the earthquakes. Older, heavier houses (mainly pre-1970s) with heavy brick or concrete-block veneer and concrete-tiled roofs, seemed to suffer more structural damage than newer, lighter buildings.

Buildings with heavy roofs tended to have more lining damage than those with light roofs, and sinkage into soft soils appeared to be more severe for buildings with heavy brick cladding and heavy tiled roofs 

The design flexibility of COLORSTEEL® also means it can be used to re-roof any structure. This is good news for older houses with sagging and damaged rooflines created by the weight bearing requirements of tiles. 

By re-roofing with lightweight metal such as COLORSTEEL® a home’s appearance and weather tightness can be restored – as well as the peace of mind of its occupants.

Earthquake-prone California has also produced some important insights. Post the 6.8 Northbridge Earthquake in 1994, Los Angeles City engineers were unanimous in saying that steel roofs are the safest in earthquakes. One structural and civil engineer summed up the situation. 

“When you put a heavy mass on your home, like a concrete roof versus lightweight steel or cedar, it causes problems when the ground shakes. Lightweight materials, on the other hand, tended to withstand shaking and didn’t appear to contribute to other structural damage. Yet hundreds of heavy tile roofs were damaged where no other significant structural damage was obvious.”

Though we may live in the Shaky Isles the evidence is clear – using COLORSTEEL® could help keep you, your loved ones and your precious possessions safe.   

 

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COLORSTEEL® Tip

Earthquakes aren’t the only natural phenomenon that can separate a house from it roof. Strong winds and weather conditions can affect a roof. As with earthquakes the secondary damage created by roof collapses needn’t be catastrophic. The lighter it is, the lighter it falls.