TropoMod - The Modular Tropical Earthship
Earthship Eco Homes’ Tropical Earthship design. These "modules" can be linked together to make a bigger home or many can be built to create a little village for tourist accommodation.
Tropical “Earthship” Design Philosophy
The design of TropoMod differs from other Earthship designs because it is designed for the hot humid tropics where lots of thermal mass (tyre walls) can cause overheating especially at nighttime; however, TropoMod retains its “Earthship-ness” by sticking to the 6 Earthship principles:
1. Natural Heating and Cooling
TropoMod is intended to naturally (passively) provide comfortable indoor comfort conditions and to do this the four factors that influence human comfort must be addressed: air temperature, air speed, humidity and radiant temperature (e.g. from a hot surface).
TropoMod avoids the use of thermal mass in favour of lightweight insulative materials to ensure that the constant tropical heat does not build up and get stored in the walls/floor/roof of the building. This prevents the issue of radiant heat causing discomfort. Instead of thermal mass (concrete, earth, stone etc) the walls are insulated with hempcrete, a super sustainable insulation material. This is a radical departure from typical Earthship designs which are high in thermal mass due to the rammed earth tyre walls and thermal mass floors. Please note, the typical earth-tube (or “cooling-tube”) system typically used in Earthships is not useful or appropriate in the hot humid tropics mainly because the ground temperature is similar to air temperature throughout the year.
TropoMod uses cross-ventilation strategies to improve airflow (an important comfort factor in the tropics). It also uses convection (hot air rising out of roof vents) plus low wattage ceiling fans to boost comfort levels in extreme heat, when the wind is not blowing. A raised timber floor will also improve ventilation and decouple the building from the relatively warm ground temperature.
Shading is a good (and cheap) way to prevent the structure from heating up and causing issues with radiant heat, so a pergola structure around the building enables deciduous vines or shade sails to shade the building in summer while allowing sunshine into the building in winter.
The high humidity of the tropics is a difficult issue to deal with especially if you are trying to avoid conventional air-conditioning systems. Provided the air temperature, air speed and radiant heat issues are dealt with adequately, humidity may not be a significant issue. TropoMod incorporates lime renders on the interior walls and this may help due to the natural tendency of lime renders to absorb excessive moisture. (I realise this might be a bit of a stretch due to the constantly high humidity in the tropics – the lime can’t absorb moisture indefinitely in the absence of occasional low humidity conditions). A heat pump water heater (located in a cupboard in the bathroom) may help due to their dehumidifying effects. Extractor fans to exhaust humid air from the kitchen and bathroom will also help. Otherwise, a small reverse cycle air-con system could be installed and powered directly from the off-grid renewable energy system, hence no carbon emissions.
Heating should not be needed right? Wrong! At times it still gets cold enough for many people to rug up and crouch by a heater, so a small pot belly stove has been located near the kitchen where it can double as a place to boil the kettle without the need for electricity or gas.
In summary, TropoMod aims to provide comfortable indoor conditions passively for the majority of the time; however, occasionally, it may be nice to use some of the “active” systems to make it super comfy inside (ceiling fans, pot belly stove, maybe a small air-con run by solar power).
2. Natural and Recycled Materials
Tyres filled with gravel will form the waterproof foundation of the ferro-cement dome structure and raise the building up off the ground to create a space for the biotanical cells (greywater garden beds) around the home. Raising the building will also help in flood prone areas.
The walls will be insulated with hempcrete which has the main ingredient of hemp hurd: a natural material which is very durable with excellent resistance against termites, mould, fire and water.
Bottle walls are an iconic Earthship design element that we will be using in some of TropoMod ’s hempcrete walls.
In summary, like any “Earthship” many of the materials will be natural or recycled/reused, but of course some materials are not natural (e.g. steel roofing, PVC plumbing, cement) however, they have been selected for their durability, thermal properties and hence they contribute to the overall sustainability of the project.
3. Off Grid Power
A renewable energy system will be installed to provide the minimal energy needs of the home.
4. Off Grid Water
The roof is designed to collect water in a tank under the house. A pressure pump and filter system will provide filtered rain-water to the home.
5. Off Grid Sewage Treatment
All sewage will be treated biologically, on-site, using the typical Earthship systems, the main difference being that the “botanical cells” (garden beds) will be located outdoors rather than indoors.
6. Food Production
The botanical cells (see above) are a great place for growing food because the wastewater is full of nutrients.
Other Earthship Strategies
TropoMod also uses other typical Earthship strategies:
TropoMod Design
The modular design enables you to start small and add-on later which helps you manage your budget.
Another important aspect of the modular design was to address the threat of cyclones. A series of smaller modules presents a smaller area to the wind and their round walls divide (and conquer!) the wind whereas a big straight wall would experience huge pressure in a cyclone and be likely to fail.
In conclusion, TropoMod is a new design that re-imagines many of the Earthship design principles with a view to developing an improved design for Australia’s hot, humid, cyclonic, tropical climate.
The design of TropoMod differs from other Earthship designs because it is designed for the hot humid tropics where lots of thermal mass (tyre walls) can cause overheating especially at nighttime; however, TropoMod retains its “Earthship-ness” by sticking to the 6 Earthship principles:
1. Natural Heating and Cooling
TropoMod is intended to naturally (passively) provide comfortable indoor comfort conditions and to do this the four factors that influence human comfort must be addressed: air temperature, air speed, humidity and radiant temperature (e.g. from a hot surface).
TropoMod avoids the use of thermal mass in favour of lightweight insulative materials to ensure that the constant tropical heat does not build up and get stored in the walls/floor/roof of the building. This prevents the issue of radiant heat causing discomfort. Instead of thermal mass (concrete, earth, stone etc) the walls are insulated with hempcrete, a super sustainable insulation material. This is a radical departure from typical Earthship designs which are high in thermal mass due to the rammed earth tyre walls and thermal mass floors. Please note, the typical earth-tube (or “cooling-tube”) system typically used in Earthships is not useful or appropriate in the hot humid tropics mainly because the ground temperature is similar to air temperature throughout the year.
TropoMod uses cross-ventilation strategies to improve airflow (an important comfort factor in the tropics). It also uses convection (hot air rising out of roof vents) plus low wattage ceiling fans to boost comfort levels in extreme heat, when the wind is not blowing. A raised timber floor will also improve ventilation and decouple the building from the relatively warm ground temperature.
Shading is a good (and cheap) way to prevent the structure from heating up and causing issues with radiant heat, so a pergola structure around the building enables deciduous vines or shade sails to shade the building in summer while allowing sunshine into the building in winter.
The high humidity of the tropics is a difficult issue to deal with especially if you are trying to avoid conventional air-conditioning systems. Provided the air temperature, air speed and radiant heat issues are dealt with adequately, humidity may not be a significant issue. TropoMod incorporates lime renders on the interior walls and this may help due to the natural tendency of lime renders to absorb excessive moisture. (I realise this might be a bit of a stretch due to the constantly high humidity in the tropics – the lime can’t absorb moisture indefinitely in the absence of occasional low humidity conditions). A heat pump water heater (located in a cupboard in the bathroom) may help due to their dehumidifying effects. Extractor fans to exhaust humid air from the kitchen and bathroom will also help. Otherwise, a small reverse cycle air-con system could be installed and powered directly from the off-grid renewable energy system, hence no carbon emissions.
Heating should not be needed right? Wrong! At times it still gets cold enough for many people to rug up and crouch by a heater, so a small pot belly stove has been located near the kitchen where it can double as a place to boil the kettle without the need for electricity or gas.
In summary, TropoMod aims to provide comfortable indoor conditions passively for the majority of the time; however, occasionally, it may be nice to use some of the “active” systems to make it super comfy inside (ceiling fans, pot belly stove, maybe a small air-con run by solar power).
2. Natural and Recycled Materials
Tyres filled with gravel will form the waterproof foundation of the ferro-cement dome structure and raise the building up off the ground to create a space for the biotanical cells (greywater garden beds) around the home. Raising the building will also help in flood prone areas.
The walls will be insulated with hempcrete which has the main ingredient of hemp hurd: a natural material which is very durable with excellent resistance against termites, mould, fire and water.
Bottle walls are an iconic Earthship design element that we will be using in some of TropoMod ’s hempcrete walls.
In summary, like any “Earthship” many of the materials will be natural or recycled/reused, but of course some materials are not natural (e.g. steel roofing, PVC plumbing, cement) however, they have been selected for their durability, thermal properties and hence they contribute to the overall sustainability of the project.
3. Off Grid Power
A renewable energy system will be installed to provide the minimal energy needs of the home.
4. Off Grid Water
The roof is designed to collect water in a tank under the house. A pressure pump and filter system will provide filtered rain-water to the home.
5. Off Grid Sewage Treatment
All sewage will be treated biologically, on-site, using the typical Earthship systems, the main difference being that the “botanical cells” (garden beds) will be located outdoors rather than indoors.
6. Food Production
The botanical cells (see above) are a great place for growing food because the wastewater is full of nutrients.
Other Earthship Strategies
TropoMod also uses other typical Earthship strategies:
- Easy to learn, do-it-yourself construction methods that enable educational “natural building workshops” to happen. This reduces labour costs and empowers people with “sustainable” skills and knowledge.
- An easily scalable design – this reduces the costs of design and engineering for future similar designs.
- Modular design enables future expansion/replication.
- Utilising “natural phenomena”, Earthships work naturally by harnessing, sun, rain, wind, the stable temperature of the earth and physical and biological phenomena (such as hot air rising and oxygen-pumping plant roots). TropoMod defends itself against cyclones, not through brute strength, but naturally, through aerodynamic wall and roof structures.
TropoMod Design
The modular design enables you to start small and add-on later which helps you manage your budget.
Another important aspect of the modular design was to address the threat of cyclones. A series of smaller modules presents a smaller area to the wind and their round walls divide (and conquer!) the wind whereas a big straight wall would experience huge pressure in a cyclone and be likely to fail.
In conclusion, TropoMod is a new design that re-imagines many of the Earthship design principles with a view to developing an improved design for Australia’s hot, humid, cyclonic, tropical climate.