Sunday, September 22, 2013

A Unique, Passively Cooled Home in the Tropics

Kotaro Nishiki built a passively cooled home in Leyte Philippines at 11 degs north latitude that incorporates a number of unique cooling features that allow the home to be cooled passively and without electricity.  Definitely worth a look if you live in a hot, low latitude climate.

In this area, most homes are constructed of concrete, and the concrete structures tend to absorb solar heat during the daytime, and then retain that heat through the night making the homes uncomfortable. Kotaro's design is centered on eliminating these daytime solar gains.

Leyte is quite warm summer and winter, so solar heat gains is to be avoided all year long.  At 11 degrees north latitude, the  winter sun shines on the south side of the house, and the mid summer sun actually swings into the north and shines on the north side of the house.  He keeps the whole house shaded using these techniques:

  • The south facing single slope roof has on overhang on the south that keeps the south wall in shade most of the day.
  • The north side of the house is shaded by an roof extension sloped down to the north that shades the north side of the house most of the day.
  • The roof is double layered with airflow between the well spaced layers.  This greatly reduces solar heat gain through the roof.
  • The east and west walls of the house are double wall construction with a couple feet between the walls.  The shading that the outer wall offers plus airflow between the double walls keep the wall temperatures low.
  • In addition, he has worked out ways to take advantage of the night temperature drop and to use thermal mass on the basement to provide some cooling.

I think that even homes that are mechanically cooled could utilize some of the Kotaro's techniques to reduce heat gain and AC energy use.

Kotaro's website provides more detail, diagrams and pictures of the house ...



  1. I have a garage with a layer of vinyl siding on the asphalt roof. The first half had siding laid horizonally maybe 3/4 off the deck. The second half I fastened from soffet to ridge, with a 1/4 " of recycled foilface styro foam under it again with 3/4" air gap in the same direction. The horizonal covering peeled off in two places and needs to be replaced. I will probably remove it and add 2x4 s on edge or metal 2X4 studs and then make the covering from soffett to ridge. Australian versions of this technique call for screen to keep the bugs out. I don't see any in this model. I should be able to compare the roof sections easily once its complete. Any thoughts about using the metal studs?, rust is not much of a problem. In central Texas rain is something you dream about...

  2. I'd like to hear how that works out. Maybe you can keep track of some before and after temperatures in the garage for a while?

    Seems like the galvanized metal studs should give a good life. I suppose a coat of RustOleum might not be a bad idea to extend the life?
    Is the new roof surface white?


  3. Note passive cooling only works when the nighttime temperature consistently drops below your comfort level, which is usually 68-75F.

    Really, if the night temp is always above about 72F, then you are better off with a tightly sealed, well insulated house and a little active cooling.

    1. true to some extent, but there seems to be to be this design conflict in high temperature, high humidity climates between insulation of various methods to stop heat egress, and encouraging air circulation to combat air humidity.

      but air circulation obviously lets in the heat you have studiously been trying to keep out

      what is the answer?

      maybe the most effective/3efficuient soltion is indeed to focus on preventing heat egress, and using ceking fans for air circulation.

      of course there is a formula to calculate the lesser discomfort of humidity with lower temperatures.

      therefore my conclusion is that is more logical and effective to design as suggested above.

  4. If you reverse the design then it is applicable for solar heating in a passive house design !


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