Block Oven Houses / by Andre James

If you were to drive around most residential neighborhoods in Trinidad, you will notice that many of the houses are freckled with air condition units. Inside you’ll probably see awkwardly placed oscillating fans in each of the many rooms. When it comes to thermal comfort in the Caribbean, we are faced with a simple design problem: we have to keep a space cool and dry. To do this, most homes end up relying on auxiliary systems such as A/Cs and standing fans.

The preferred method of home construction in T&T and the West Indies is plastered, concrete/clay block walls topped with some type of metal roof, with minimal -if any- insulation anywhere around the building envelope. Roof overhangs are shallow and windows are usually small punched openings with single pane metal windows. Our homes are big, boxy and compartmentalized, room by room.

Big, boxy and compartmentalized

One afternoon, I noticed that one wall of my bathroom was noticeably warmer than the adjacent wall. This wall faces west and captures most of the day’s sun. The temperature along the entire length of this western wall was consistently higher than any other wall of the house. I started to wonder how much this heat can affect the temperature of the adjacent room, or the rest of the house for that matter. Has this wall become a 15-foot radiant heater? Are these walls contributing to heat to the home? Is the masonry wall the best wall type for our climate?

I used an infrared thermometer to take readings on the inside and outside surfaces of the exterior walls of the house. I measured the temp. of an interior wall as a control. I expected to find that the interior surface temperature of a sunbathed wall, would be considerably higher than the other walls in the house, maybe close to its exterior surface temperature. However the results were a lot more subtle than I expected.

Even though the exterior surface temperature got to as high as 45°C, the inside face of that wall never got past past 32°, which was only 3°more than both the shaded adjacent wall and the control temp taken at the interior wall. The walls absorb a substantial amount of the sun’s energy, keeping it from reaching the inside. Though it is possible to reduce the total heat gain of the building by insulating the building envelope, based on these temperatures, I just don’t think it will be worth the additional cost. Concrete is a great insulator. It is also a great thermal mass which poses a different issue.

The heat that is absorbed by the wall throughout the day is then released into the cooler night air, adding heat to the space. While the interior surface temperature remains at 30°C, the exterior temp goes to as low as 27° thanks to air circulation. It is at this point the concrete works against us, keeping the interior temperature higher by insulating the space from cooler exterior temps. The same material that keeps us from roasting is actually also keeping us warm at night. Instead of changing the wall construction, we need to increase natural air circulation throughout the home in order to achieve close to exterior temperatures.

Trinidad and Tobago has become increasingly dependent on air conditioning and other forms of artificial cooling; our way of building may have even enabled it, without our air conditioners, our houses are closer to ovens, sealing in the heat instead of exhausting it.

With our government subsidizing energy just over $1.5B USD per year, T&T enjoys some of the cheapest energy in the world; it is cheaper to artificially condition space than to develop sustainable building practices. At least for now… What happens when the subsidy stops? Are you prepared to pay at least double what you’re paying now for electricity? Still want to rely on that A/C?