From Heritage New Zealand, Winter 2009

by Jamie Douglas

Committed owners, heritage advisors, and the government are all taking a firm stand when it comes to strengthening heritage buildings against earthquakes

Earthquakes are a part of life in New Zealand. Nestled uncomfortably on a tectonic plate boundary our landscapes, landmarks and ourselves have been shaken up, literally, since the country was formed. Adding to this tectonic game of halves is our position on the Pacific Ring of Fire – a hot spot for earthquakes and volcanic eruptions.

It’s not exactly a solid foundation on which to build but, true to form, New Zealand’s pioneers made a start, their handiwork evident in many ornate, character-filled heritage properties that are still part of our streetscapes today. But age, forces of nature and compliance with modern building safety codes mean many of our heritage buildings are at risk. How we get the best of both worlds – a combination of old and new buildings in which the public can feel safe – is a balancing act.

Earthquake-strengthening and the techniques and legislation required to safeguard and future-proof New Zealand’s earliest built heritage are a challenge and can be costly. But they can result in architectural innovation such as that used in the building of the Old Public Trust Building in Wellington – this year celebrating 100 years– with its skeleton riveted steel frame helping to fend off the perils of moving ground.

However, there are losses, as evidenced most recently by the 6.8-magnitude Gisborne earthquake in December 2007 at a depth of 40km. Buildings in the central business district partially collapsed and roofs caved in. The Civil Defence Controller and Gisborne District Council declared 23 sites unsafe and 11 still had restricted entry the following day.

Concrete evidence

A significant proportion of heritage buildings under the microscopes of owners, developers and local authorities dates from 1880 to 1930, a period marked by an increased use of unreinforced masonry. While wood was favoured over brick for residential buildings because of its ability to flex under stress (still the case today), central-city buildings were built predominantly of brick because of the risk of fire.

Alison Dangerfield, New Zealand Historic Places Trust Architecture Heritage Advisor, says that from the early 1900s reinforcing was being used by architects in heritage buildings. “There were various architects experimenting with reinforced steel to see if they could improve structural capability in earthquakes. The obvious places to start were at the foundations and door lintels. For many heritage buildings it was enough to hold them together in an earthquake. Of course there are a number of buildings that haven’t survived.”

She points to two early-20th century success stories in Erskine College and Chapel and St Mary of the Angels, both in Wellington. At Erskine, load-bearing brick masonry walls, including a concreted reinforced bond beam at each floor, are a technological feature while St Mary’s features reinforced concrete and brick with a timber roof supported by concrete arches with steel tie rods.

Other techniques to earthquake-strengthen heritage buildings
included diagonal steel bracing and lining with structural shear walls to provide lateral resistance to counter seismic activity. However, Alison says they were often used in disappointing ways and are not well regarded in heritage circles. “The important thing now is to use appropriate techniques so that the strengthening does not dominate a heritage building.”

While no one engineering technique can be guaranteed earthquake-proof, those being developed are helping in protecting heritage buildings, Alison says. These include bracing with steelstraps in the roof, sheet bracing such as plaster board, plywood and particle board, reinforced concrete walls or floors and concrete masonry walls. “When structural upgrade work is undertaken, engineers try to work out which are the vulnerable places in a building and do something to boost them. With earthquakes it’s usually lateral forces [where one side of a building moves while the other stays fixed] and the joints that are susceptible.”

Architect and conservator Ian Bowman believes New Zealand engineers tend to err on the side of caution when assessing at-risk buildings, possibly underestimating the strength of the existing building. He says architects were significantly influenced by the 1906 San Francisco earthquake, in which more than 3000 people were killed, in designing and adopting strengthening techniques. “Hoop irons, steel straps in masonry buildings laid in the mortar bed to tie it together better and the steel-riveted frame for the Public Trust Building in Wellington: these techniques were followed. A lot of research has gone into retrofitting earthquake-strengthening into heritage buildings. New Zealand engineers are up there in world terms. Base isolation, for example, where the building is isolated from the ground by sitting it on rubber, was invented by New Zealander Bill Robinson. Examples of this in Wellington include Parliament Buildings, the Maritime Museum and Te Papa.”

Owners’ obligations

For heritage property owner Peter Dowell, there is no better time than the present to protect heritage buildings. Joint Managing Director of Heritage Property Management Ltd, he part-owns 12 Wellington central business district heritage buildings. As well as being geared to a financially viable long-term business practice, Peter’s motives are clearly driven from the heart.

“We are a relatively young country but we’ve already lost a lot of our built heritage to the wrecking ball, especially during the 1970s and ’80s. If we don’t save our heritage buildings, what will we have to show where we have come from? I’ve worked in New York and London and when you tour cities in Europe you see how these old buildings make up a huge part of the cultural fabric.”

While the social, visual and tourism benefits are compelling reasons for protecting built heritage, the reality is that owners must face up to costs and regulations. Prior to the 1931 Hawke’s Bay earthquake, New Zealand had no building code. Since then there have been successive codes developing the structural performance criteria for buildings. However, meeting the requirements of the Building Act 2004 has been an issue for some owners who have opted to pull down or adopt a demolition-by-neglect attitude which presents not only a public risk but also the loss of historic buildings.

Peter says ultimately it comes down to money and whether owners are prepared to see their investments as long-term projects.

While subsidies from incentive funds are available, there is a heavy reliance on private capital to retain heritage buildings. A major issue owners face with the Act is that even a small planned change of use for a building can trigger a requirement for earthquake-strengthening.

He contends that with the majority of heritage buildings being two storeyed, a revision of the Act needs to be considered. “In Christchurch, for example, you have heritage buildings with first floors the owners can’t lease out because of the change-of-use provisions and the cost of meeting standards. They’re sitting there empty. It’s almost a forced case of demolition by neglect. If you leave buildings empty because the cost is prohibitive, nature will destroy them anyway.”

Ian Bowman expresses a clear and simple message on the value of retaining New Zealand’s built heritage. “Architecture is a work of art. Heritage buildings tell us a lot about the past. They have values that we want to retain for the future.” He prepares between 10 and 20 conservation plans each year with projects that have ranged from the large scale, such as the $35 million conservation of the Auckland Town Hall and the $10 million Regent Theatre project in Palmerston North, to work on the East Takaka School Hall in Golden Bay.

In his dealings with heritage owners, Ian works with others who share his values and, despite the costs involved in earthquake strengthening, finds there is a willingness to comply with standards set. “Heritage owners tend to take a responsible attitude. That’s why they come to people like me, because they want to protect their heritage property.” He says those with whom he has worked are” pretty realistic” in acknowledging what needs to be done. “From a personal safety point of view they want their occupants protected.”

Tremors through time

History gives examples of nature’s power and why, with an evergrowing population living among ageing buildings, earthquake strengthening is required. The April earthquake in the Abruzzo region of central Italy which measured 6.3 on the Richter scale and killed more than 290 sits alongside New Zealand equivalents. Geonet, a collaboration between the Earthquake Commission and GNS Science, records around 15,000 earthquakes within New Zealand each year with up to 250 strong enough to be felt.

New Zealand’s strongest recorded earthquake was in Wellington in 1855. With a magnitude of 8.2 it not only redefined the physical layout of the burgeoning town but also laid waste to brick buildings of the time. Most single-storeyed wooden houses survived, despite shifting on their foundations and being damaged by falling brick chimneys. In terms of comparative strength, the recent Italian earthquake sits alongside Gisborne’s 6.8 magnitude in 2007, Edgecumbe’s 6.3 in 1987 and Inangahua’s 7.1 in 1968.

The loss of life and scale of destruction in the 7.8 magnitude Hawke’s Bay earthquake in 1931 were the catalyst for introducing building guidelines in New Zealand. Two hundred and fifty six people were killed and much of central-city Napier turned to rubble when a large number of unreinforced brick buildings collapsed. Although there have been floods, earthquakes, landslides and volcanic activity since, there has not been a disaster on such a scale.

Safety codes

Alison Dangerfield says that before the Napier earthquake, architects and engineers were aware that some buildings were vulnerable to the intense and horizontal shaking associated with earthquakes. Afterwards, the need to change building design radically “took a leap”. “From this time on, architects and engineers looked very closely at ways to strengthen and stiffen buildings. Steel was seen as an ideal material because of its tensile strength. It had been used prior to 1931 but after that date was used more extensively in anticipation of another earthquake – in foundations to hold the building upright, in walls to stop floors collapsing and throughout the building to allow people to survive.”

The government developed and introduced a national building code in 1935 although it was not mandatory. Standards of design and construction to enable buildings to resist the horizontal motions from ground shaking were recommended. Masonry buildings had to be firmly bonded so the structure would move as one unit. The first national mandatory building code was introduced in 1965. There are a number of heritage buildings in need of earthquake-strengthening to meet the standards of the 2004 Building Act which helps to identify and put in place steps to ensure public safety and health. There has been a varied response from individual councils to identify heritage buildings and reduce earthquake risk as part of building compliance. It is up to them to set incentive funding and the timeframe to earthquake-strengthen buildings under their jurisdiction.

Ian Bowman believes that in terms of regulations, the 2004 Act is “better than it was” but improvements, including a more centralised approach in assisting heritage owners with funding incentives, could make it still more effective. “The Act has brought in the issue of built heritage. How it’s being interpreted may be a different issue but there’s the ability to do it right.”