Much of our research and experience involves cold climates, but what about passive solar design for warmer or more humid areas?

If you dive into most resources devoted to natural building history, materials, and legacies, you’ll no doubt find a whole lot on mud bricks from the ye olde days in middle England, some rammed earth from the extensive archive of amazing climate-resilient design from north Africa and the Middle East, and some work in stone from Europe and northern and central Asian areas.

But what about those who have lived and adapted quite successfully over millennia in more humid tropical areas? What are the tricks and things to think about when designing using natural materials in warmer climates, and what to look out for.

In Australia, there are well-known designers such as Troppo Architects who have been working in this field for a while and have developed a range of designs that cater to the specific conditions of the tropical north. But how natural are these builds? Who is building with natural materials in tropical climates and how do these houses work?

Passive Design:

At the core of these ideas is a passive house design. ‘Passive design’ works with the environment to exclude unwanted heat or cold and take advantage of sun and breezes, therefore avoiding or minimising the need for mechanical heating or cooling. Passive design in the tropics means designing a building to make the most of natural light and cooling breezes, and using shading, orientation and appropriate building materials to reduce heat gain and storage. The use of passive design principles in the tropics results in a building that is comfortable, energy efficient and results in substantial savings in running costs of both cooling and lighting.

Buildings designed for tropical climates must focus on providing shading to reduce direct sunlight exposure, using natural ventilation to increase airflow, incorporate thermal mass to regulate indoor temperatures, and use moisture-resistant building materials to avoid issues with mold and moisture.  They can also benefit from good orientation, proper insulation, and energy efficient appliances to reduce heat generation.

Let’s focus on each of these points as an introduction to designing for the tropics.

Shading:

Orient the building to reduce exposure to midday sun, particularly summer sun. Optimize for nearby shade (trees or vines). Use verandahs and deep balconies to shade and cool incoming air. Use landscaping to provide shade without blocking cooling breezes and use planting to reduce ground temperature and minimise reflected heat.

Air Flow:

Encourage natural ventilation by orienting the building and windows. Create cool outdoor areas. Include operable windows and ceiling vents that enable the building to naturally ventilate. Align vents, windows and doors to allow air flow through the building – these should be aligned in a reasonably straight line for maximum effectiveness.

Minimise internal obstacles or blockages such as internal walls in major flow through areas to allow for unimpeded ventilation. Raise the building off the ground to catch breezes.

Design for convection air flow to remove hot air from the building. Convection air flow is created by hot air rising and exiting at the highest point, which naturally draws in cool air from outside. This natural cycling of air can be created by placing low window openings across a space from high window openings. This will be even more effective at cooling if incoming air is being drawn from a shaded area where plants are growing

Thermal mass:

Thermal mass refers to the ability of building materials to absorb, store and release heat.

In tropical climates, the use of lightweight construction materials with low thermal mass is preferable, particularly on walls that are exposed to the sun. This is because lightweight construction materials such as timber, respond quickly to cooling breezes allowing the building to cool faster. These materials still require insulation to prevent direct heat transfer and to improve the efficiency of mechanical cooling if used.

High thermal mass materials work best in temperate climates where there is

a significant change in temperature between night and day. During summer, the heat stored in thermal mass during the day is flushed out by the cooler night temperatures, and the cool stored in the mass over night is released into the building during the day.

Warm nights in the tropics mean that heat is not flushed from the thermal mass and instead radiates back into the building.

Use of high thermal mass construction materials is therefore generally not recommended in the tropics. If high thermal mass materials are used, the building should be well shaded to avoid heat gain and insulated internally to reduce heat transfer. Recent research has shown that innovative, well insulated and shaded thermal mass designs have been able to lower nighttime temperatures by 3 to 4°C in tropical areas with a low level of temperature fluctuation between day and night.

Insulation and the mold issue:

Higher levels of insulation can lead to less energy transfer through the building envelope which slows or prevents drying of any moisture present in the wall assembly. In addition, tighter envelopes can result in higher concentrated air leakage areas.

Without adequate air ventilation, this can lead to mold, bacterial growth and rot, which ultimately can impact the durability and safety of the structure and the health and wellbeing of its occupants. However, it is possible to effectively prevent mold if you understand the fundamentals.

That’s where mold- and mildew-resistant insulation and other water-resistant building materials should be considered with every project to create a healthy and productive living environment.

Wall assemblies need to be constructed to suit their unique climate zone, since each zone will experience different moisture/rain and humidity levels, and temperatures.

Natural clay plasters are a proven way to reduce mold growth in almost any space. There are 2 properties that work to this end:

•     clay’s incredible moisture “breathing” quality
•     clay’s natural anti-fungal properties

Earth plasters are created without any modern preservatives or fungicides, and the tests show that they reduce the propensity for surface mold growth.

Check out this blog post of a family doing their own clay walls.

All month we will be focusing on the options and benefits of passive design and natural materials for tropical climates so check back in soon.