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Insulating Buildings and Homes

How to Insulate Your Home and Keep Cool

Keeping cool in a hot climate can be very expensive in air conditioning costs.

Here we look at why our houses get hot through radiation, conduction and convection and steps we can take to insulate our houses and reduce our air conditioning bills.

Keeping comfortable in a hot climate

aluminium roof insulation

For many people who are acclimatised to life in a tropical climate an open building with well designed ventilation and extensive air circulation provides a comfortable living environment.

The use of rotating roof ventilators, ceiling fans and a building design that catches the prevailing breezes can achieve this.

Inevitably there comes a day, however, when the ambient temperature soars and personal comfort falls. We desperately need to find relief so we switch on that ever so expensive air conditioner.

The High Cost of Cooling

Those of us from cold climates are familiar with brass monkey weather and we know only too well the importance of good insulation but for some reason, in hot climates, we never seem to give it a second thought now do we? The good news is that insulation can save a lot of money and give us a better lifestyle.

Air conditioners use a lot of power and for many people they make up the lion’s share of their electricity bills. A typical room is 4 metres by 5 metres, 20 square metres.

If it is a well insulated room we will need a 1.25 HP air conditioner which will take just under 1 kilowatt to run (see the air conditioner calculator at

If the room is medium insulated we will need 1.3 kilowatt air conditioner.

If it is poorly insulated the power needed will jump to more than 2.5 kilowatts. To run a 2.5 kilowatt air conditioner for a year will cost around Rp 28 million!

If we are paying so much for our cold air we can save a lot of money by insulating our buildings.

What is Heat?

Let us start at the beginning and look at what heat actually is. Heat is energy stored in molecules in the form of excitement, yes excitement. When we add energy to a molecule it gets agitated and starts jumping around like a scalded cat. The more energy a molecule of a material has the more excited it becomes and the hotter the material becomes.

Rather like a good old dose of ebola heat likes to share itself around. If we add excitement to a molecule this makes the molecules around it get excited and the heat gets passed on. The heat will carry on transferring until all the molecules are all equally excited - ie. all at the same temperature.

Heat Transfer

Heat can be transferred in three ways:

  1. Radiation - Infra red rays from the sun (and to a lesser extent, from other hot surfaces) are rays of light and even though we can’t see them they can travel through the vaccuum of space. These infra red rays transfer their light energy into any molecules they strike as heat.
  2. Conduction - heat is transferred through materials and between different materials. Some materials, such as copper and aluminium, conduct heat easily while others, such as air, conduct heat very poorly.
  3. Convection - Movement of hot air or water carries heat with it, it collects heat from anything hotter than itself, it moves on and transfers the heat to anything it meets that is colder than itself.

Heat can also be transferred in any combination of these.


To keep our buildings cool first we need to be aware that cool is of course an absence of heat. In cold climates we need to generate heat then stop the heat escaping from our homes. In hot climates we remove heat (with and air conditioner) and we stop heat from getting in. This reversal is, of course, obvious but it makes an important difference about how we go about insulation.


In hot climates radiation is the greatest heat factor we have to deal with. It is also our first line of defence so, to avoid infra red rays radiated from the sun and from hot things around us, we can do the following:

  • Shade our building by using roofs, trees or anything else to shade our walls.
  • Put solar film on our windows to reflect heat (this does not necessarily have to be dark in colour as we are reflecting infra red rays which are not within the visible spectrum).
  • Install aluminium foil (or any other reflective material) in roofs and/or walls to reflect heat.
  • Paint walls or flat concrete roofs with white paint (shiny if possible) to reflect sunshine.
  • Avoid reflective surfaces, such as tiles, that reflect heat into or at our buildings.


The outside surfaces of our houses are still going to get warm so for our second line of defence we can use can use insulating materials and/or air gaps to prevent the transfer of heat through roofs, walls, ceilings, floors doors and windows.

As we have said air is a poor conductor of heat as long as the air is not moving. Insulation materials such as glass wool, rock wool, expanded polystyrene, bubble wrap or double layer aluminium foil with a layer of closed cell sponge in between work by holding pockets of air and preventing this air from circulating.

The use of cavity walls (effectively two walls with an air gap in between) greatly reduce the amount of heat being transferred through walls.

Double glazed windows are similar, they have two sheets of glass with an air gap (usually partially evacuated) in between which greatly reduces the transfer of heat through windows.

We need to avoid the use of materials that can transfer a lot of heat very quickly (most notably copper and aluminium) passing through the floors walls and roofs of our buildings.

You might also have noted that these materials also provide insulation against sound such as traffic or those endlessly barking dogs.


The third thing we can do is to stop convection. Probably our greatest loss of our precious cold air is through the movement of air. We open a door and our expensive cold air flows out across the floor. Even a large gap under a door has a major effect.

We must prevent the movement of hot air into or the loss of cold air out of our buildings by using draft excluders and seals on windows and doors. We also will need to seal up holes such as air vents in walls and above windows, exhaust fans and don’t forget holes around air conditioner pipes.

An important concept in convection that we all know but must constantly bear in mind is that hot air rises and cold air falls. If we are clever we can use this to our advantage.

To summarise here are some steps we can take to reduce the cost of cooling our homes:

Low cost

  • Install UV reflective film on window glass
  • Install window blinds (on the outside) to shade windows.
  • Install draft excluders along the bottom of doors.
  • Install seals around windows.
  • Make doors self closing.
  • Paint external walls white.
  • Put a layer of small pebbles on your flat concrete roof, these shade the roof while having minimal contact to transfer heat.
  • Plant trees and bushes that can shade your building.

Medium Cost

  • Install aluminium foil insulation under your roof tiles, note that double layer foil with a closed cell foam in between the layers is more expensive but works better.
  • Ventilate your roof space, it is best if air can enter under the eaves and exit along the ridge.
  • Install insulation such as glass wool above your ceilings.
  • Install thresholds with in built seals under doors.

High cost

  • Extend roofs and/or install canopies so they shade the walls through most of the day.
  • Install double skinned roofs.
  • Install insulating panels in your ceilings and/or walls.
  • Build double layer “cavity” walls using insulating building materials.
  • Install double glazed window units.
  • Provide “air lock” door arrangements.
  • Insulate your floors.

Avoid internal sources of heat

Many household devices produce heat, cooking stoves, electric kettles, toasters, hair driers, water heaters, washing machines and showers all heat our homes. Even our old incandescent lights - 80% of the energy used by an incandescent light is heat. Leds are much better because they produce very little heat.

Designate “cold” rooms and ventilated rooms.

It is a good idea to decide that some rooms such as bedrooms will be air conditioned while other rooms, especially kitchens and bathrooms, will always be cooled by ventilation. This greatly eases the difficulties and costs of insulation particularly in kitchens where cooking is constantly producing heat and exhaust fans are often running.

If the weather becomes too hot then you can retreat to the designated cold rooms.

Move To A Higher Altitude

Altitude of course makes things cooler and those people who live in Ubud know only too well that the short distance from Southern Bali up to Ubud makes a huge difference in terms of temperature and comfort.


You may have noticed that I have not mentioned humidity and, as we all know, this has an important bearing on how hot or cold we feel. This is a whole subject in itself that you can read about here.........

Copyright © Phil Wilson November 2016
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