Designing for Flood Plains

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Built Higher, Built Better, Built to Last

Immediately following the 2011 floods Architects Black & Wilson were approached to design a new commercial office building to replace the original building destroyed by flooding of the Brisbane River.

Brisbane City Council required any replacement building to be flood proof and required the floor level be 1000mm above the prescribed flood level for the site. This required the floor level to be 3600mm above the existing ground. Any enclosed areas on the ground floor had to be minimized and basically flood proof.

Following design of the new building and obtaining Development Approval the project was delayed for several reasons and the DA extended once. Twelve months before the DA lapsed the project was resurrected and the project was raised up again like the Lazarus Effect. A change in requirements over the six-year hiatus meant the design had to be altered. The changes had to be sufficiently minor so that they the design remained “generally in accordance with the original approval. Reapplying for a new DA would have further delayed construction. We had to comply with some additional development requirements that were introduced during the hiatus.

Elevating the building 3600mm above the ground presented enough difficulties on the site another metre increase in height would prevent the project form proceeding. Being built on a flood plain the foundations were essentially mud, so piles were required to be driven down 12 metres to support the new building. It was also decided that all plant and equipment should also be located above the flood level. Further the sewer and water had to be designed to prevent backflow contamination.

Naturally the 2011 budget had to stand 6 years later. The construction methodology had to change to the most economical possible without looking cheap. The final solution opted for was concrete columns and tilt up walls supporting a concrete floor slab – all designed to withstand any future flood surges. More economical domestic construction technologies were adopted for everything above the floor raised above the flood level. This included prefabricated a treated timber wall and roof structure. Not only did this significantly reduce on site waste but it also sped up construction. The roof went on a few weeks after the suspended floor slab was poured.

Sustainable Material Selection

A lot of effort went in to making the building as sustainable as possible. Some argue that concrete has a lot of embodied energy and is therefore not green but in this case constructing a building that can be destroyed and require early replacement is the epitome of sustainability. Materials above the flood zone like the roof and wall cladding are all recyclable (on site) and all the timber framing is sourced from sustainable software. It is all about life cycle sustainability.

Insulation and Energy Efficiency

Energy efficiency was also paramount and the building incorporated many energy efficient features. In addition to double wall insulation the building boasts thick roof and ceiling insulation.

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Larger overhangs improving sun control.

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Good Design Keeps this Building Covered

Large overhangs provide the required sun control during the day and the tilt concrete panels to the east and western ends of the building provide thermal mass protection from the rising and setting sun. This means the load on the air conditioning system is minimized. The soft start twin scroll compressors are the most sophisticated and efficient available. Spiral diffusers spread the air more effectively than standard square diffusers. DC fans also are provided to the open offices to increase psychological cooling which will enable the running temperatures to be reduced in summer.

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Natural lighting, radial diffuses and ceiling fans to minimise energy.

Glazing lets in Natural Light

The lighting has sensors to recognize natural ambient light levels and the LED lights adjust accordingly. Due the large amount of (energy efficient) glazing there is so much natural light the internal lights are often not turned on. The lighting has heat and motion detectors and the lights turn off when rooms are not occupied. Glass between office spaces provides visible connection while separating deparments and controlling noise.

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WYSIWYG What You See Is What You Get.

The whole project was designed and documented entirely in 3D (three dimensions) making it very clear to the corporate executive what they were going to be delivered – get right down to the toilet roll holders. The client and staff are all very happy with the finished building which was completed in the month the DA was due to lapse. Despite the 3D modelling the building surpassed the client’s expectations in that they never quite realized how the elevated building would provide the opportunity to look over the rest of the recycling facility from the new offices.

Following the 2011 floods many businesses have relocated out of the area to higher more expensive ground. Surely designing a building to be reborn like Lazarus is a preferable sustainable solution.

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The computer image is pretty close to actual building.