It Makes Sense, Insulate Your External Walls!


Insulated Exterior Walls a must with every home built in hot climates.

Have you ever wondered why most builders in North Queensland insulate the roof of a new home, but not the external walls? After all, the sun shines on more than just the roof. When choosing a new home design a lot of factors need to be considered. In order to make a fully informed decision, all of these factors need to be known. The most important of these factors is insulation. To really appreciate the effectiveness of insulation, you need to know how the suns energy impacts on the interior of a home. Firstly, unless you completely shade or insulate the entire exterior of a home, the sun’s heat/energy will penetrate to the inside. As a result, it becomes uncomfortable to live naturally and the Air Conditioners run constantly. All material absorbs heat/energy from the sun in some degree, and will in turn radiate that heat to the other side. Therefore, careful selection of material used to construct the external walls of a home is very important. Consider the following designs;

  1. Masonry block walls with steel reinforcement (cyclone strength) and core filled with more concrete.
  2. Timber framed walls with steel and timber reinforcement (cyclone strength), an external lining of reflective foil, 70 mm bulk wool insulation and finally a 20 mm air cavity.

How does each of these designs work in the heat of the tropics? Let’s now look at each design with respect to absorption, conduction and radiation of heat. Firstly, design Option 1. Masonry is very good at absorbing hot energy and holding that heat. The heat absorbed by the masonry/concrete will be slowly released to the cooler side of the home, so shading is very important if this design or material is selected. If the entire surface, of all walls on the home, is shaded by earth or dense vegetation then this material is effective. This is because it will be cool on the outside and absorb heat from the inside. Masonry/Concrete or clay bricks are very good as internal walls that absorb heat from the inside during the day and release the heat back into the home as the temperature drops during the night. However, masonry external walls not shaded will absorb the sun’s energy and release that heat slowly into the interior of the home during the night making living very uncomfortable.

The other solution when using masonry/concrete, although not as effective, is to insulate the walls. This will reduce the amount of heat, being released by the masonry, penetrating into the interior of the home. This solution now has three layers for the sun’s energy to penetrate. The masonry block, bulk insulation and finally the plasterboard lining. The downside is the masonry block wall would be larger in width; approx. three times that of the second design.

Secondly, design Option 2. Insulated exterior wall timber framed, as a standard construction practice, has multiple layers of insulation. To be precise five layers of insulation. The first is the external lining followed by reflective foil, and than 70 mm bulk insulation. The final two layers are the 20 mm air cavity and the plasterboard lining. The heat is absorbed by the external lining and up to 97% is reflected by the foil lining. The remaining heat radiates through to the bulk insulation, which is a very poor conductor of heat. As a result, the heat cannot build enough energy to heat the next layer of defence, the 20 mm air cavity. The last layer is the plasterboard lining, as you can appreciate this does not get heated by the air cavity and released into the home. This design almost eliminates the sun’s energy from penetrating at all.

In conclusion, the first design option as a standard practice is not insulated and to do so creates a very wide wall. The second design is always insulated with five layers and is only half the width of the first design. This is important when the interior living space is sacrificed by the width of the exterior wall. In any situation, insulation to any material used for construction of a home’s external walls is a must. Although, why make it difficult? Select carefully the material used to build your new home.

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