How to build a hollow block house in the Philippines, or any place in the tropics and keep it cool. Concrete/hollow block houses with metal roofs are the norm in the Philippines and elsewhere in tropical Asia. Filipinos don’t build such houses out of ignorance. They have critical advantages. They resist typhoon damage. If they’re flooded, they can be cleaned out and used again. For the most part they are termite proof. Locked up at night, they provide pretty good security to residents. They are mostly built with low-tech local materials by local workers well versed in building with concrete and hollow blocks. Such houses can be quite inexpensive. So, in most respects they are very well suited to the Philippine tropical context, but there is one huge and notorious disadvantage — they are so hot. The mass of block and concrete bake in the tropical sun and this retained heat is re-radiated into the house day and night.

Compounding the problem is the metal roof which can turn the attic into an oven. The overall effect is a house which can be markedly hotter than than the outdoor temperature and very uncomfortable. Our own apartment is routinely over 90 degrees inside even when it’s in the 70s at night. The coolness of the tropical nights don’t penetrate our bedrooms which remain hot all night. It’s painful to switch on the air conditioning when just outside the walls is a lovely, comfortable tropical night.

Here’s how we are trying to avoid this fate in our new house. Firstly, we tried to design the house to resist the sun. Our eave overhang is almost 1.5 meters, almost 5′. The overhang, combined with the relatively low eve height outside (about three meters) and big windows placed high on the walls, keeps most the sun from the windows and minimizes sun on the concrete building itself. The house is mostly shaded from the midday sun — say from 9am to 3pm. We’ll plant plants, shrubs and trees to further keep the sun out of and off of the house. It’s amazing how many Philippine houses are designed with little or no regard for the tropical environment in which they will be situated. The main focus seems to be on grandiosity.

We also really focused on keeping the roof and attic cool. We used a very light colored reflective roof material. Such reflective roofs reflect much more of the solar radiation than the more popular dark colors. Dark colors such as dark red, dark green, brown and terra cotta are popular because they mimic the look of clay title but this is a triumph of appearance over comfort. Houses with absorptive roofs need bigger air conditioning units which have to work harder to disperse the absorbed heat. With no aircon the house is just hot.

Our next step was to install reflective metal foil underneath the metal roofing. This reflects back a significant amount of the radiant heat that makes it through the roof. Next is a 25mm layer of fiberglass bat insulation. The foil and fiberglass insulation were add-ons to our roofing contract. The fiberglass insulation is referred to as “ACI” insulation. ACI is a now defunct manufacturer of fiberglass bats but fiberglass is now all called “ACI” just as all toothpaste is called Colgate.

The metal roof is screwed to steel roof supports called purlins. The roof installers wanted to put the fiberglass insulation over the top of the purlins and then screw-down the sheet metal roofing. This of course would have totally compressed the fiberglass at the purlins, reducing its insulative value. Just imagine installing fiberglass batts over studs rather than between them and then nailing on plywood sheathing!

Of course the notion of insulation is much more foreign to the Filipino than to those of us from the north where insulation is a fact of life and survival. While they did not really understand my objection to compressing the batts, they agreed to install it the way I wanted it installed. They drilled holes through the 3″ high metal purlins and threaded a network of 16 gauge wire to support the bottom of the insulation. The wires were spaced every 20cm.

The reflective foil did not come attached to the fiberglass batts so the workers manually glued the foil to the batts using contact cement. This sounds awkward but went well. First they sawed the 120cm wide rolls of fiberglass in half to create batts to fit between the purlins which are spaced 60cm on center. The batts, with the foil up, where laid over the network of wires and then the roof panels were screwed down. The wires were 1.5″ down from the top of the purlins so that there was a 1/2″ airspace between the underside of the roof panels and the reflective foil. This is ideal.

The end result is a reflective light colored roof, a 1/2″ airspace, reflective foil and then 25mm of fiberglass insulation. This combination should make the house several degrees cooler. In fact it seems to be working. Since the roof was installed, we’ve had very hot weather but the house seems cool. There was no added cost for the light colored roof. Our roofing came from DN Steel. They call the color “beige”. The foil and the fiberglass added about P50,000, installed. The roof also has two large ventilators at the peaks and will have soffit vents to further control heat in the attic area.

The roofing and insulation was purchased through Far Eastern Hardware on Quezon Street in Iloilo City.  Victoria Ang is the person to contact: cellphone 63-918-888-2228.  Her crew installed the roof .  Victoria has an engineer she sent to help us when our crew had problems following the roof plans.  This was a huge help.  We purchased much of our building materials and power tools from Far Eastern and can recommend them.  They never tried to short or cheat us or to supply undersized materials.  It’s also a great place for the builder.  They stock just about everything including AEG, Makita and Bosch power tools and all the accessories such as cobalt and carbide drill bits, cut off saw blades, grinding wheels and so forth.  We standardized on Bosch supplies and AEG power tools.  Whenever we post this kind of recommendation, there is a certain percentage of readers who assume that we must get something in return.  We don’t.  We have no relationship with Far Eastern except that of a satisfied customer.  It is we who like to reward those who have treated us honestly with our recommendation to others and to help our readers with our experiences.

There are other things we’ve done and will do to make the house cool. Our property is located in an open and very breezy agricultural area. We put in exceptionally large (240 x 160 cm) windows casement windows. We like casement windows because 100% of the window opening can be open, whereas sliding windows leave 50% closed, even when the windows are fully open. We also put two windows in each bedroom for cross ventilation, except for one room. Since the windows are exceptionally large, thermal mass is reduced and air circulation increased. Our ceilings are over ten feet high. Each will have a Hunter ceiling fan.

Theory confronts reality update 2-5-11. The triangular roof vents shown above have been closed off with sheets of plywood on the inside.  Our site is so exposed and windy that storms blow rain in through the ventilators.  This threatens to damage our Hardiflex ceilings.  It does not help that the ventilators almost precisely line up with the prevailing winds, the “Amihan” NE monsoon and the “Habagat” SW monsoon.   Such ventilators might work fine in a more sheltered location, but ours is anything but.  Fortunately, we have a large soffit ventilator in each corner plus other roof vents in the porch ceiling.  Some easy means of opening and closing the vents is a project for the future.

It’s our hope that all these things will combine to reduce the interior temperature of the house by several degrees compared to what it would be without the steps we took.  Our house is still a concrete house exposed to the hot sun.  The things we have done have kept the house cooler.  Much of the year no air conditioning is needed.  The advantages of our big windows are especially obvious.  Our rooms are wonderfully bright and if there is any breeze at all, the rooms are quite comfortable unless it is very hot and still.

We rented an apartment in a concrete house that had poor ventilation.  It was like an oven.  Air conditioning was needed almost year round.  Our house is infinitely better, mostly because of our breezy location and big windows.

Here’s the big difference.  A concrete house with small windows and poor cross ventilation will be hot inside no matter what the weather is outside.  A house with big windows and good cross ventilation will be hot when it’s hot outside, but cool air will flood the house in the mornings and evenings.  The house will be more pleasurable because of the fresh air and will not require air conditioning when it’s cool outside.  It very hot at the time of year we write this, around 37C or close to 100F midday. Because we don’t have window screens yet (see our post about that) we keep windows closed at night to keep the bugs out.  As soon as Bob gets up at 5:00 or 5:30am, he opens all the windows.  The house cools off almost instantly as the 75F air pours in and stays quite comfortable for the next five or six hours.

We’ll use our two air conditioners during the hottest weather, but far less than than we did in our oven-like apartment.   We’ve planted dozens of trees.  When they are all big enough to shade the house, it will be cooler still.  Building a “cool house” does not transform a house in the tropics but it can, at very little cost, make it more comfortable more of the year and save far more in air conditioning costs that the “cool house” features themselves cost.

Electricity is expensive here.  At present it’s almost 25 cents (US) per kwh.  Much of it is produced by coal burning power plants. Incorporating “cool house” features will  money and reduce your use of  coal-fired electricity.

Listen to “The Chilling Facts about Air Conditioning” podcast on Tom Ashbrook’s “On Point” at http://www.onpointradio.org/2010/05/chilling-facts

Lots more reading on cool roofs at the Lawrence Berkeley National Laboratory http://coolcolors.lbl.gov/

NYT: White Roofs Catch On as Energy Cost Cutters http://www.nytimes.com/2009/07/30/science/earth/30degrees.html?_r=1

http://www.fsec.ucf.edu/en/publications/html/FSEC-CR-1220-00-es/index.htm

(Apologies to those who find this post duplicative.  It’s just a new summary of previous posts.)