Roof top research could pave the way for greener buildings

A living, growing experiment has been built on top of the Engineering Building at the University of Auckland to test the city's suitability for "˜green roofs'.

Researchers from the Faculty of Engineering turned the roof into a 18.58-square metre garden.

This three-year research project will look into design specifications for green roof systems suitable for both new developments and to retrofit existing structures.

"Green roofs are an ideal solution for reducing stormwater run-off that pollutes our waterways, destroys aquatic life and causes stream erosion, which can lead to flooding. They also have the added benefit of creating habitats for birds and improving insulation," Paul Walbran, ARC Councillor, and deputy chair of the council's Environmental Management Committee said.

Elizabeth Fassman, a lecturer in Civil and Environmental Engineering who is leading the project, says green roofs overseas have reduced stormwater run-off by 50 to 90%.

"We would like to know if our locally sourced materials work as well as the materials that have already been proven overseas, and if so, establish the best combination of materials," Fassman said.

"We're not just throwing up some soil and plants, we have very carefully selected porous materials that can hold a lot of water. When they are dry, they weigh almost nothing."

The roof has been divided into six plots with different combinations of lightweight mediums being trialled in each, including pumice, zeolite, imported expanded clay and bark fines. Soils are not used as they are too heavy for most existing roofs to withstand.

The plots have been planted with 3600 plants, a combination of natives and sedums, or succulents, selected for their hardiness and ability to withstand droughts or floods. Ideally the roof will be able to absorb up to 35 mm of rain, which will eventually evaporate back into the atmosphere.