Christie Walk Factsheet
Introduction
Christie Walk is an ‘eco-city’ development in Adelaide, South Australia. The goal of this housing project is to create a liveable, affordable and environmentally benign urban community that provides a practical prototype for the ecological development of our cities.
The project consists of 14 dwellings which include linked four three-storey townhouses with full solar orientation, a three storey block of six apartments with east-west orientation, four standalone cottages and a ‘community house’.
Another 13 dwellings will be added with the construction of Stage 3 - a 5 storey apartment block facing onto Sturt Street.
As of early 2007, some 42 people live at Christie Walk, ranging in age from less than one year to over 80. Site population density is therefore 210 people per hectare (42 people on a 2000 square metre site).
Christie Walk as might be seen from the North East
Aims
The design brief demanded energy efficiency and high overall ecological performance allied to user-participation in the development process and an ethical investment funding base. It was intended to demonstrate and trial both the problems and possibilities of ecological, ‘community-driven’ development on urban sites. Concerns ranged from broader issues of community participation to the detail of specifying materials for creating non-toxic, healthy homes.
Strategy
The overall strategy was to use high internal mass within highly insulated skins with multiple user-controlled ventilation options and thermal flues. Vegetation and outdoor spaces were designed to be integral with the house designs as part of the passive design approach. Smaller house plan areas were favoured with the quality of space being seen as more important than mere quantity; this is most clearly demonstrated in the first cottage to be built on the site, a two-storey, two bedroom strawbale house of just 55 square metres.
A range of dwelling types are represented in the project with differing configurations, orientations and construction systems to demonstrate the efficacy of environmental design for various conditions and lifestyles.
Plan and Orientation
Each dwelling is individually planned at the same time it is planned to fit with its neighbours to create an urban environment of secluded gardens. Balancing privacy and the provision of shared community space was a major requirement that is addressed by the creation of an internal pedestrian street designed on the theme of a walled garden.
The 2 and 3 storey cottages are detached structures whereas all the 3 storey townhouses are linked.
Solar control for the cottages and the apartments is almost entirely to do with morning and afternoon sun. The other dwellings possess ‘classic’ north-south solar orientation. Solar access angles controlled building heights and form within the site and solar access to the neighbouring childcare centre was protected by careful design of roof profiles.
Location
With reduced car park provision and no internal traffic, the site is being developed to take advantage of its inner-urban location within walking distance of Adelaide’s Central Market and a full range of public transport services.
Site
The project is on a T-shaped site the size of two quarter-acre blocks in inner-city. The constraints of the site make it impossible to provide all the buildings with ‘classical’ north-south orientation. Adelaide’s climate is ‘Mediterranean’ with warm to hot summers and cool winters. It is subject to ‘cool changes’ when temperatures can plummet from the high 30s to low 20s in less than an hour. Although the City of Adelaide virtually never experiences freezing temperatures it can feel very cold. Buildings need insulation to keep heat in during cold weather and to keep heat out in hot weather.
The site is small, awkwardly shaped, and severely constrained with buildings hard on or close to most of the boundaries.
Site Impact
The site was occupied for predominantly commercial and some residential use prior to its current redevelopment. The overall site impact might be regarded as positive as the project will be retaining all stormwater on-site and there will be considerably more productive and vegetated landscape after redevelopment than before.
Shell Fabric
Construction includes 300mm thick load-bearing autoclaved aerated concrete (Thermalite) for all external walls on the apartments and townhouses. 400mm load-bearing poured low-strength concrete (‘earthcrete’) for the internal mass party walls between townhouses.
There is some steel framing in the apartment building construction (which have reinforced concrete slabs on all floors), and timber-framed (loadbearing), rendered 500mm strawbale walls for the cottages.
Pinus radiata proprietary trussed joists are used in the townhouses with plantation pinus or recycled timbers for joists in the cottages. Floor decking is generally Ecopanel, a compressed straw equivalent to particle board that contains no woodchips or formaldehyde. Unfortunately, the Australian company that made the sheets no longer operates and any equivalent product would now have to be imported.
All the buildings are set on very stiff reinforced concrete slabs designed to resist the effects of Adelaide’s notorious movable clay soils. The high volume of material content of the slabs necessary to carry the townhouses and apartments is justified by the small building footprints and their long design life.
The planned life of the buildings is in excess of 100 years during which time the shells – made from mined materials - are expected to remain much the same whilst internal partitions, doors and windows – made mostly from renewable materials - may be changed.
Heating and Cooling
Some ceiling fans are included to assist in maintaining air flow on difficult, still days, but there are no heaters or airconditioners and the expectation is that none will be needed to supplement the passive heating and cooling of the houses.
Each house works as a ‘thermal flue’ allowing controlled release of warm air whilst drawing in filtered, cooled air from the vegetated, landscaped surroundings. The apartments rely on good cross-ventilation and high thermal mass for cooling with the roof garden adding a thermal buffer to the upper floor apartments.
Thermal mass
The concrete slabs provide substantial internal mass, particularly to the cottages and apartments (With no freezing days perimeter insulation of the slabs has not been regarded as necessary). The ‘earthcrete’ walls place additional thermal mass between the townhouses and assist in noise reduction between dwellings. The cost and logistical problems associated with the poured concrete technology prompted a change to thick masonry walls in the apartment/townhouse buildings.
Ventilation
Good
ventilation is critical to the performance of these buildings. Filtered, cooled
air is provided by surrounding vegetation and landscaping to be drawn through
the dwellings by convection. Many opening windows are small, top-hung and
set low in sets of two or three to draw in the low lying cooler air. Purpose
designed vents, high level louvres, or ventable skylights exhaust warm air
at the top of the dwellings, creating outlets for the thermal flues that are
formed by the stairwells of each dwelling.
Insulation
Insulation is provided by 300mm Thermalite walls to the townhouses and apartments and 450mm strawbales to the cottages. The basement possessed by one of the townhouses is insulated by earth berming and provides additional ‘coolth’ to that dwelling. Ceilings generally follow the roof lines and are insulated with reflective foil sarking and R3 polyester batts (Tontine) which contain a high percentage of recycled PEP plastic. The preferred option of cellulose fibre (recycled paper) insulation was not an option because of the sloping ceilings.
Glazing and Windows
Windows are all purpose-made from recycled timber with aluminium flyscreens (justified on the basis of long life, low maintenance and almost 100% recyclability).
All windows are double-glazed except for some small opening windows which are expected to be open most of the year and they create only a small heat sink during heating months.
Sealed units are used throughout except for double timber beaded double glazing to the first two storey strawbale cottage.
Lighting
Considerable effort has been made to ensure naturally well-lit rooms and spaces. Light fittings are conventional with a mixture of compact fluorescent and incandescent globes.
Hotwater and Fittings
All dwellings have solar hot water with electrical backup heating – gas backup was not practical for multi-storey use. The apartments have a shared system with banked solar panels and a single pump and backup heater. Low water use shower heads*?! and in-line flow restrictors control the water supply. Underbench filters provide drinking water at very low flow rates.
Energy Supply
Mains electricity is drawn from the grid but photovoltaic panels set on pergolas over the apartments’ roof garden will generate electricity for sale to the local energy utility. The expectation is that the site will be a net energy exporter for much of the year as the dwellings require little energy for space and water heating, cooling or lighting.
Major appliances
AEG is the preferred supplier for the project and all new appliances have high energy efficiency ratings. Companies with a recycling program were favoured when specifying appliances. 5 of the dwellings have gas cooktops, all dwellings have high efficiency electric ovens. Gas was initially favoured for its energy efficiency but the improved efficiency of electric cookers and increasing concerns regarding indoor air quality issues have led to developer specifying electric-only appliances in the latter stages of the project.
Materials
Non-toxic construction and finishes are used throughout with a policy of avoiding formaldehyde and PVC. Timbers are plantation (pinus radiata) or recycled (typically, oregon). The environmental plus cost criteria for materials led to unexpected choices with aesthetic benefits, eg. purpose-built spiral stairs in steel and recycled jarrah. .
All concrete in slabs and mass walls contains the maximum percentage of flyash that the engineers and suppliers (Pioneer Concrete) would allow. Flyash is a waste product from power stations and its use reduced the amount of new cement used in the construction. Cement production is one of the largest single global contributors to greenhouse gas emissions.
Floorings and finishes
Flooring throughout is generally Marmoleum by Forbo, a modern variant of linoleum that was selected on its aesthetic merit and environmental credentials – it consistently tops the list of ‘green’ proprietary flooring materials in studies around the world and allows a rich design pallet of colour and pattern. Wet areas are tiled with ceramic tiles with local products preferred. Some clients, including the owner of the first strawbale cottage, chose bamboo flooring in some areas. This attractive and environmentally promising material is currently only available as an imported product but Australian plantations and production are imminent.
All finishes are chosen on the basis of environmental and non-toxic criteria. Paints, varnishes and stains are all by BioProducts, produced in Bridgewater, SA under license from a German company.
Stormwater
All water shed by the roofs, balconies and other impervious surfaces is collected for use on site in two 20,000 litre underground tanks situated beneath the carports. After filtering, the water is used for irrigation and toilet flushing thus reducing total water importation to the site.
Greywater and Blackwater
A grant from the Clean Seas Program of the National Heritage Trust allowed purchase of an onsite chlorine-free sewage treatment system. Effluent was directed to an "electroflocculation" sewage recycling plant which extracted water for use in sub-surface irrigation on the roof garden, and deposited the solids in an underground tank, where it would compost, and then be pumped out every few years for use as fertiliser in rural areas. Unfortunately the system did not prove to be satisfactory due to the high cost of operation, and was decommissioned. Other options are being pursued.
Landscaping
Low water use plantings favour native and indigenous species. Some exotics have been chosen where appropriate to suit passive design considerations (the largest tree will be a deciduous Jacaranda). Exotics and productive food plants are supported by on-site water recycling to maintain minimal overall water consumption.
Waste Minimisation
Paving, carports and feature elements incorporate bricks, stone, steel and timber retrieved from demolition of pre-existing structures on the site.
Noise Control
The highly insulated external skins, double glazed windows and massive party walls make this a much better acoustic environment than might be expected in a dense urban setting. The passive cooling strategy requires windows to be open much of the time but the baffling effect of vegetation and absence of smooth hard road surfaces contribute to relatively good noise control.
Transport and Food
Reduction of transport demand and provision of food production capability were part of the strategy for this project.
The site’s location within walking distance of good public transport meant fewer cars were needed and the Council planners supported a lower than usual car park provision (initially 10 spaces for 13 two and three bedroom dwellings).
Despite extreme site limitations, it was possible to include a small community garden to demonstrate that even the tightest urban site can produce food.
House Prices
House prices (which include a share in community areas and facilities) range from $150,000 to over $400,000. The non-profit structure of the development cooperative and building company was an essential part of keeping house prices in a range comparable to conventional inner-city properties in Adelaide.
History
The site was purchased at a fortuitous time and this helped to keep development costs down. On the other hand, the building structures are relatively innovative in an Australian context and possess exceptional levels of insulation, for instance, which has incurred a cost penalty. An individualised approach to each dwelling design also added costs.
The structure of the first completed building, a strawbale cottage, (as well as the other strawbale cottages, now under construction), was put in place by volunteer labour which helped reduce ‘start up’ costs in the building program. Most of the construction has been via a conventional building contract augmented by volunteer labour.
The timeline for the development was stretched by a series of unforseen circumstances but the relatively low percentage interest rate of much of the ethical investment funding base assisted the co-operative in withstanding the resulting financial pressures. The building program for the townhouses has been about 20% longer than for conventional construction.
Cooperative Development
The project was designed for a group of clients represented by a development cooperative, Wirranendi Inc, created by Urban Ecology Australia. The clients included first-time home buyers, investment purchasers, experienced home owners seeking the advantages of an urban lifestyle and older people wanting to retire in the context of an active, mixed community.
The land was owned by the Wirranendi development co-operative during construction and individual properties were then sold on a community title. Each purchaser owns their own dwelling but also shares ownership and responsibility for the landscaped community areas, that include a community garden, and a ‘cohouse’ (community house) with a kitchen, small general purpose hall (great for parties that won’t fit in small apartments!) and a laundry.
Evaluation
There have been no major problems obtaining development and building approvals and the development process has been very resilient. During construction the death of one of the most active people involved with the project meant that for his partner to stay in the project a rapid and substantial redesign was needed to reduce the size of their dwelling. This was successfully achieved. The non-profit development structure, ethical investment base and community involvement enabled this experimental project to proceed and to withstand delays and personal tragedies and survive where a conventional development approach would probably have resulted in the project being been abandoned or changed beyond recognition.
The ‘earthcrete’ wall created difficulties in construction and cost more than anticipated. As an attempt to provide affordable high mass construction and as an alternative to rammed earth it is a qualified, moderate success. The building designs are yet to be proven through occupation and use over more than a few months but the signs are that they will be successful. There is a tremendous sense of ownership and understanding about the designs that both reflects and reinforces the community basis of the development approach. People have been able to purchase much more than just a house in the city. The community house is an important part of the project as both a physical facility (including the laundry essential for building approval of the apartments planned with no internal laundry) and as a community meeting place. Its construction has been contingent on a voluntary self-build co-operative approach that cannot necessarily be readily replicated in all situations. This would be reflected in overall purchase prices for any comparable development elsewhere.
Likewise, the use of recycled material and resident requirement for residents to lay the external paving may result in creative, attractive environments but would add costs to any project not able to tap the same level of commitment and goodwill from its clients.
Rigorous cost planning requires good information which wasn’t available the first time around, but details and costs associated with the innovative approaches to construction and design have now been tested and refined making it much easier to predict programming and costings for future developments.
More financial resources would make it possible to accelerate the development process so that it was competitive with conventional development, and would assist in maintaining the active engagement of a wider community with the design and development program.
More time would make community engagement more effective and easier to maintain.
Project Credits
Architecture and Urban Design: Ecopolis Pty Ltd (Project Architect: Paul F Downton) www.ecopolis.com.au 0411 823 248
Project Manager: Ed Wilby
Structural & Mechanical Engineer: Sagero Consulting, Adelaide.
Builder: EcoCity Developments Pty Ltd, with sub-contractors
Community processes: Urban Ecology Australia Inc.
Landscaping: Ecopolis (Chérie Hoyle) with Jacqui Hunter
This fact sheet is based on a case study initially prepared by Paul Downton for the Australian Greenhouse Office new residential design guide ‘Your Home’ Technical Manual, with modifications by Emily Alfred (UEA intern from October 2001 to April 2002). Updated in 2005 by Michael Robertson.
2007.5.1