No more than tree canopy height proposed for Christchurch rebuild

Right now in Whitehorse, a town in the North East Canadian province the Yukon, the city planning department is seeking to change some bylaws to help solve the issue of a lack of housing. One of the proposed changes?  Removing a building restriction that currently only allows buildings to be built to a maximum height of four storeys. But that restriction exists for a reason and links to a rebuild approach being proposed by New Zealand landscape architect Di Lucas, former president of the NZ Institute of Landscape Architects.

Whitehorse is located close to a fault line and the main reason given for the limited building height is that it helps mitigate damage, should an earthquake strike. But it also has an aesthetic function. Limiting the height prevents buildings from blocking out too much sunlight, which in the winter can be a precious commodity in the Canadian North.

And following on from this people and environment-focused design, Lucas is recommending the rebuild of the Christchurch CBD should seldom be higher than four storeys. She proposes using tree canopy heights, typically three or four storey’s high, as a form of measurement, and cites Noosa on the Sunshine Coast of Australia as a good example.

“Noosa on the Sunshine Coast formalised their height limits to tree canopy height, and everyone loves that city,” says Lucas. “You don’t need to see the sea from within the centre, you can sense it, and enjoy the microclimate from a low rise environments.”

Lucas completed an analysis for the Civic Trust 20 years ago, she says now is the time to reconsider this approach as Christchurch looks at re-building options.

“The current City Plan lacks design controls and measures to make the CBD beautiful and sustainable. An urgent change is needed. We don’t want just utilitarian structures,” says Lucas.

“We need a city with the X factor, to attract businesses, workers and visitors. Not again draughty spaces below high-rise and exposed to the easterly; buildings ignoring the solar resource; and, outmoded transport options. We could change it from a tired energy-hungry city to an appealing sustainable garden city.”

Lucas proposes this be achieved through the use of natural systems, including maximising the use of local materials, installing greening roofs, managing rainfall with permeable surfaces and creating micro-climates via the creation of vegetated public and private spaces.

And don’t forget Christchurch’s precious wetlands. Having reviewed maps from the 1850s, Lucas notes evidence of an explosion of old levees (the natural stream banks made of silt) from the September and March earthquakes. 

“Fifty percent of buildings in the CBD will likely disappear because of the earthquake. The old maps show some were built above streams apparent at that time. The 1850 mapping suggests the PGG building which collapsed in February was likely built on a levee of silt. The land surface of Christchurch is deceptive, as it was a dynamic plains system,’’ she says. 

And that, according to Lucas, should serve as a reminder that the underlying natural state of land needs to be carefully considered in the new city layouts. 

recent aerial photo showing streams from an 1850 map

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