Creating a sustainable building solution in tropical climates has its own very specific set of challenges.
Dr Lisa Law, an urban geographer at James Cook University (JCU) in Australia’s tropical North Queensland, thinks the major issue for green building in the tropics is that the building code and rating systems have been developed for the temperate southern states. These solutions, she says, often do not translate well in hot, humid climates like Cairns and Darwin.
Although there are three climatic zones in the tropical areas of Australia, these regions are typified by high temperatures and high humidity, as well as distinct wet and dry seasons. It is hotter during the wet season because of the high humidity, with temperatures reaching as high as 50 degrees Celsius. The large amount of rain leads to frequent flooding.
There are six primary focus areas deemed critical for achieving best practice sustainable tropical design: Planning and Management; Site; Design; Materials; Energy; and Water.
PLANNING AND MANAGEMENT
This includes the sustainable planning and management of the whole building process from site selection to occupation.
Very specific considerations need to be factored in, such as managing construction sequencing to allow for wet season impacts and the selection of suitable, durable materials, and construction detailing to minimize the impact of condensation, moisture traps and mould caused by the humid environment.
Regarding the latter, Anissa Farrell, senior associate – sustainability manager at architects Conrad Gargett, says managing the construction workforce is imperative.
“Skilled labour is a big issue,” she said. “There is a real shortage in top-end Australia.”
Farrell also believes the sharing of knowledge relating to both successful and poor project outcomes in the tropics, where the experience can be used to promote better outcomes for future buildings, needs the support of building associations and the Architects' Institute.
A more unusual area is tropical health consideration, which includes pest and disease control in communities and around buildings.
But perhaps the hottest topic currently is planning for safe and resilient buildings in areas prone to severe tropical weather events. This issue is being addressed with the development of the Building Resilience Rating Tool (BRRT).
A component of this is the Building Resilience Knowledge Database, a portal of information on the resilience of building products and materials to extreme weather events. BRRT will provide a comprehensive listing of all building materials available in Australia, such as roof tiles and insulation blocks, and list how durable they are to certain risks, such as saltwater inundation or hail damage.
Sustainable site choice, location and management helps minimise harm to the ecology, and enhances site amenity, promotes healthy communities and creates resilient communities.
Maximising resilience and minimizing isolation during extreme weather events is again a key consideration. This means having an in-depth understanding of coastal, rainforest, highland and savannah micro-climates to prepare for floods, storm surges and cyclones.
Increased rainfall during the wet season, for example, requires solutions to control the volume and quality of stormwater run-off to minimize erosion and sediment/nutrient loos to waterways.
Key sustainable building design strategies include effective passive design for hot, humid climates to minimise solar heat gain, and maximising natural ventilation (cross ventilation and thermal venting) to reduce reliance on non-renewable energy, and support well-being
Here, careful specification of doors and windows is important. They need to maximise cross ventilation when open, protect the opening from rainfall, provide a good seal when closed, have glass that minimises conduction and radiant heat transfer, and be designed and installed to meet high cyclonic wind speeds.
“Roller shutters have the greatest impact on a home during cyclones yet are the cheapest item to replace,” said Farrell. “Current BCA section J requirements require air tight design which is not suitable for tropical climates – this is a cold climate European response.”
When it comes to materials, Farrell says it is all about whole-of-life strategy.
Products, materials and finishes need to be carefully specified to minimise corrosion, deterioration and maintenance in the heat and moisture of tropical environments.
Proprietary systems and materials that rely on rubbers, adhesives, sealants, silicones, resins and binders, for example, may be subject to deterioration or delamination faster in the tropics due to high heat, humidity and mould.
Materials that out-gas VOCs should be avoided as high humidity and heat may accelerate the release of toxic substances.
Reducing reliance on electrical energy, whether through good passive design and/or renewable energy sources, is more than just good sustainable best practice, says Farrell. It also allows communities to recover more quickly after extreme weather events.
Great solar access in tropical latitudes means more opportunities for PV energy sources and solar water heating. Other innovative energy technologies are particularly suitable for tropical climates. The wet tropics have an abundance of water to produce hydroelectricity, and water sources may also be used for heat transfer technology.
The rising cost of infrastructure provision is another challenge, but clever design and use of technology around water demand and supply can provide a significant reduction in mains water usage.
For instance, the use of rainwater tanks and onsite recycling can produce benefits such as a reduction in the use of pipe quantities, reticulation energy and waste treatment.
Another benefit may be reduced erosion through a reduction of water flows that are diverted from water courses in peak rainfall periods as well as reduced flooding risks in urban areas.
The Great Barrier Reef International Marine College (GBRIMC) in Cairns by architects Conrad Gargett demonstrates many of these core principles in practice.
The challenge here was to create an inspirational facility from a very limited budget that had a distinctive marine character while embodying environmentally sustainable initiatives where possible. Techniques used included:
With a prominent north-facing building orientation the design acknowledges basic passive design principles and additional passive climatic responses where acquired through the placement of rooms based on use and facade treatments.
Passive design initiatives include the provision of external and internal shading to the classrooms and office glazing to provide optimum thermal comfort and sufficient day light penetration to avoid excessive artificial light usage.
Active systems employed to reduce energy consumption include the use of mixed mode system incorporating user-operated openable windows for night time purging, ceiling fans for daytime natural ventilation and air conditioning to control tropical climate effects, flexible switching of lighting, lighting that uses movement sensors, and the use of suspended lighting to provide both direct and indirect lighting.
Indoor environment quality
One of the key achievements for the college is the proximity of classroom and workshop areas to daylight and views. From an internal courtyard, students can enjoy views to the landscape and featured immersion pool but also beyond to the Great Dividing Range and Trinity Inlet that frames the site.
Other initiatives include the use of low-VOC paints and carpets, zero formaldehyde joinery and increased ventilation rates, all of which improve the indoor environment quality for both teachers and students.
Water use strategies within the college have been managed through capture (roof water collection and water sensitive design), storage (underground tanks), reuse (water used for immersion pool and landscape irrigation) and reduction (low flow taps and toilet cisterns).
Whole-of-life cost optimisation resulted in material selections based on environmental responsibility, energy conservation and the capital cost balanced against operational and maintenance costs. Material selection was also based on real life boat and marine environments as part of the on-the-job training requirements for the college.