In order to have an effective insulation system we need to reflect on the reality that heat conveyed into a structure will be done so by means of Convection, Conduction and Radiation.
Convection and Conduction have been the primary focus when it comes to designing insulation materials.
SANS 204 Energy Efficiency Standard is prescriptive in the ‘R’ value interventions which are required in the building envelope.
The ‘R’ value of various insulation products is given and is different for various thicknesses and densities. An ‘R’ value is an indication of the material’s ability to resist heat flow. These values do not take into account Radiant Heat Transfer.
Due to the lack of understanding regarding the science of Radiant Heat Transfer, the design of insulation materials and insulation systems in the South African market has not been adequately addressed. Radiant Heat is responsible for about 75 % of total heat gain or loss within a structure and can be destructive as the UV penetration into a building through the roof causes damage to the services housed within the attic space, for example electrical wiring and conduit. During a typical hot South African Summer, the prevalent heat gain is by way of solar energy absorbed by the roof. The consequent heat build up then radiates heat downward toward the attic floor, then moving through the attic floor it is ultimately absorbed by the interior surfaces of your home, damaging the surfaces and at the same time also increasing the summer heat load. Walls also typically allow solar heat gain into your living space.
Radiant Heat Barriers are materials that are specifically designed to protect buildings from the harsh effects of Solar Penetration and UV damage.
In the same way, during the winter months Radiant Heat Barriers installed in your attic space and walls, will reflect much of the radiant heat back toward the source of heating.
Radiant Heat Barriers :
Perforated foils are preferable in areas where the control of moisture is needed.
Radiant Heat Barrier products should always be installed in combination with prescribed Air Gaps.
Because of the thickness of most Radiant Heat Barriers and Reflective Foil Laminates, the perception is that they are not as effective as your thicker bulk insulation materials, this is not the case, properly installed in conjunction with airspaces they are just as effective and provide an extra element of protection. By sustaining an acceptable temperature within the attic space they protect your traditional bulk insulation from excessive heat loads and a decrease in their ability to resist heat flow. Radiant Heat Barriers are therefore essential to the realization of the required thermal performance of buildings as recommended in SANS 204.
The benefits of Radiant Heat Barriers and Reflective Foils far outweigh any perceived disadvantages, and are becoming more popular as home owners discover the benefits. Radiant Heat Barriers ideally should be installed at the construction stage of your building but can be easily retrofitted, speak to your area specialist for advice regarding an installation to suit your needs.
To bring to an end to any confusion, it should again be stated that Radiant Heat Barriers and Reflective Foil products are designed to stop the transfer of radiant heat, and bulk type insulations are designed to slow down the transfer of conductive and convective heat. The two product types cannot be judged against each other. Preventing both Convective heat flow and Radiant Heat Flow has to be achieved in order to have an efficient insulation system. Therefore both Radiant Barrier technology and bulk insulation should be used jointly whenever possible.