An Urban Water Solutions document by eme group and Smart Water Fund notes that that over 90 per cent of rain that falls in urban areas is not collected for use. Instead, this run-off is discharged into waterways along with contaminated water from paved areas and roads.
Put this statistic beside the one saying that more than 85 per cent of Australians live in urban areas, and we start to get a sense of how important water management strategies and designs are for residential projects, particularly urban dwellings.
From a sustainability practice point of view, there is opportunity for the capture of rainwater for use from construction – for cement mixes to cleaning equipment – through to occupation.
According to Chris Knierim, director of Code Green, the reuse of all water in any project is paramount in minimising the impact of the local water ways and environment. However challenges abound in this arena, as issues like the type of build determine the possibility and feasibility of the implementation of water management systems.
For instance, there is more opportunity with a new build to provide cost effective solutions to water management, such as earth moving equipment having easier access to a particular area of the site to create an underground tank.
A retrofit or alterations project may not have the same provision of room, which means an above ground water tank may be the only viable option. But, as Knierim points out, logistics may not allow for the tank to be placed in the desired location. Confined spaces may also limit the size of the tank.
Containment as the best strategy
The number one solution to ensuring water management is sustainable is containing water, says Knierim, who offers some tips:
“Architects and building designers should consider the gradient of the land and if possible, utilise the gradient to guide the water course into the underground tank system.
“If the land has little gradient they should consider landscaping the land in a way that will enhance the opportunity in capturing the water while forcing the water into the landscaping and underground management systems, which allows for the water to be reused.”
Image: Stratco Aqua-Line Tank
This idea of ensuring the most amount of water is being captured and contained is echoed in all of Code Green’s construction projects, often manifest in the form of a two-pronged water management plan.
The first stage sees the team determining the most appropriate location for the underground water tank and constructing it first, before creating a series of paths that divert all rainwater onsite back into this tank. This allows them to recycle the water captured during construction, minimising the project’s dependence on the mains water supply.
The second stage is a permanent water management plan that will be implemented for use once the building is completed and occupied.
Case study: Forest Lodge ECO House
This plan was employed for Code Green’s Forest Lodge ECO House, which was officially opened by Lord Mayor of Sydney Clover Moore in January, and named one of Australia’s most sustainable inner city residential projects this year.
Eco-design principals were the launching pad for the design of this Sydney terrace house, which was built on one of the last remaining vacant land sites in the inner city. With a width of just 4.9 metres and a modest land area of only 89m2, many of the innovations and systems featured had to be specifically custom-designed for the project.
Backing up Knierim’s “number one solution”, the water management strategy of the project rests largely on a 3,500 litre underground water storage tank that provides water for the toilets, irrigation for the roof top and vertical gardens, and the rear garden’s suspended table waterfall centrepiece.
“Not only [is the project] minimising the water leaving the property, but it is also harnessing the benefits of the captured water in the underground water storage tank, which irrigates the green roof, vertical gardens and is used to support the other water usage equipment required by the house,” says Knierim.
The water storage tank, located beneath the outdoor entertaining area, also works hand-in-hand with the custom natural air ventilation system, which allows external breezes to flow through a pipe system and travel into the water storage tank to be chilled as it passes.
The hot water system has also been cleverly employed to help provide heating for the home. In an Australian-first innovation, Knierim designed a heat storage made from a layer of compacted soil enclosed in a polystyrene barrier that was laid on top of the pipework.
Hot water heated from the roof solar tubes flows via the pipe system down to this natural heat chamber, which is located a metre below ground, warming the earth and becoming trapped and stored in a compacted soil storage cell. This heat is then released on demand to warm the house’s polished concrete ground floor slab.
“The solar tubes and heat storage system were the most costly individual items purchased, but the environmental benefits and cost savings are already evident as the dwelling has to date not required any mechanical assistance for heating or cooling,” Knierim notes.
The green roof also plays a role in the water management design for Forest Lodge ECO House, not just for insulation and aesthetic benefits, but also to minimise the additional loading on the local storm water system; essentially the stormwater is managed via the green roofs, with the captured water stored in the underground water tanks.
SIKA’s water proofing membrane, a 1.5mm thick Sika Sarnafil G410-15L felt membrane, is utilised in the green roof system, while the roof barrier mesh and versi drain system were supplied by Elmich. The lightweight soils are engineered by Knierim himself to a recipe developed over the years, and which work extremely well considering some areas are only 70mm deep.