Passive design strategies..what is this?

When you live in a country like Costa Rica where pure air is constantly flowing, and after a psychometric chart study indicating that the use of the passive strategy known as Cross Ventilation you will achieve a 70% comfort without using Air Conditioning almost throught the year, then the Wind Wheel comes in handy!

Know your Holdrige Life Zone in Costa Rica and you will achieve more sustainable dwellings in an easy, less expensive and more sustainable way.Design and passive strategies analysis are the answer to building in a respectful manner.

Either of the two times during a year, one of them right today, the sun crosses the celestial equator and  the length of day and night are approximately equal; and the Sun is closest to the Earth.If you are building a tropical home in a hot, rainy and humid weather like Costa Rica, this means that you really should prepare for intense heat over your roof! And your head!

In a tropical location, roof design is the responsible architectural element that will provide comfort and quality indoor environment. In the video below, you can see how a house in the mountains of Perez Zeledon is perfectly shaded during equinox, the hottest time of the year in Costa Rica.

This video is prepared by the program I generally use called Eco Tect,this is when I can double check what my common sense tells me when I am designing at any location. This case specifically needs direct natural light during the rainy season as, so the eaves width and house orientation is determined by such technology. The process feels more like playing with the roof measurements and angling spaces in order to satisfy 2 opposite weather conditions.

To be able to truly enjoy a terrace in the tropics where you can sit all day regardless of the day’s weather conditions (sunny or rainy), an expert like an architect can help you with the design’s orientation of your home or with choosing the right shade device.One easy way of making sure you are in the proper direction, is to check shades at the location at 3 pm in the afternoon ( warmest time during the day in most parts of Costa Rica)during equinox , summer and winter solstice. If the specific location gets enough shade during these times of the year, more likely you will get enough shade all year long.  How can we do this? I personally use the EcoTect Program, a BIM Modeling system that is a great tool that allows me to design a specific overhang or shade device , horizontal or vertical, and explore  and give my client different options that will also emphasize views and good ventilation .

Here’s the typical scenario: houses near the beach usually are oriented to south west or west to maximize ocean views  also get a lot of heat coming in due to the orientation. Here’s three important ideas to create the perfect environment.

Step 1. In these situations it is extremely important to use a vertical shade device and extend the overhang up to 3,5 meters (depending on the width of the terrace) . When doing the landscape, choose trees with skinny trunk but that can grow tall.Picture2.  Horizontal shading devices do not effectively shade this terrace.Check how the terrace has no shade at all.

Tropical House design with a sliding vertical shading device that effectively drops in the correct shadow angle on the terrace.Chontales de Osa, Costa Rica.

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Right orientation of a structure in Costa Rica can be tricky. There are 10 basic types of ¨local climates¨ all over the country which result in a huge variety of different microclimates.Flora and fauna biodiversity are blessed with these conditions, and one of the main objectives of tropical modern architecture is to design with nature, adapting designs to local weather. Not adapting the weather to a house. This can probably be the main reason for construction materials not being as durable as we thought so.

Example of site analysis combined with microclimate analysis.

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As far as possible, vertical construction should be encouraged. Try to roof and pave the smallest possible area. One of the main causes of climate change,floods, erosion,accumulation of debris in the beds of rivers, dying aquifers and  accumulation of phosphates in our soils, is the excessive hardscape  and size of the buildings.
The more surface roofing area, the more reflected heat goes into the atmosphere.
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As you have noticed, I recurrently write about passive design strategies. These strategies are in few words, the part of the architecture that dedicates its studies and proposals for innovative construction techniques, based on passive traditional practices to resolve the needs of comfort, hygiene, and safety in the shelter for human activity.

With the understanding that each area and building requires special consideration for geological, geographical,geo biological, geo morpholigical matters in addition to climatic conditions, is the aim of the passive strategies to lower the possible environmental impact.

Geotecture was born in ancient and vernacular building traditions which trough trial and error and lot so f observation over millions of years, forged techniques and procedures to obtain shelter. In the Costa Rica case, the first who used these strategies were our natives from Talamanca. After a while, around the same area, europeans imported their victorian style. The local afroamerican communities tranformed it into what we know as vernacular architecture. One of such techniques used in this kind of architecture, was Crossed Ventilation. This is basically a concept to define ventilation on buildings.





Depending on each site and time of the day, there are typical winds that generate high pressure zones and low pressure zones. You should promote open windows and interior doors located specially to let the air flow generated by the 2 pressure zones, to all over the house, as homogeneous as possible. Doors and windows should be located diagonally in the space.


In reference literature specialists Givoni, Izard, Guyoy or Olygay recoomend crossed ventilation for warm temperate climates to wet tropical moist, like Costa Rica, as a strategy for passive cooling of buildings. This strategy should be used with the combination of shade and surrounding environment meaning walls and ceilings, whose surface temperature is similar to room temperature. This is closely related to roof design and wall insulation.

While the outside temperature does not exceed 30’34 degrees celsius with a relative humidity of 70’90%, we can achieve crossed ventilation. Outside these ranges the croos-ventilation strategy will be less effective. Fortunately, most areas in  Costa Rica fall within these parameters, that’s why I tend to promote Crossed Ventilation on all my projects.

I truly believe on not spending not even one more dollar or colon on air conditioned. Unless you have a special computer or medical room. Ac pumps heat and harmful gasses into the external environment, thus contributing to global warming, so we need more air conditioning. The classic ‘ vicious circle” effect. The power required to run it consumes fossil fuel, depleting reserves and again, adding to global warming. Is it good for us to sit breathing recirculated air which consists of other people’s farts, body odour, tobacco fumes and food smells?

Open your minds and windows…


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