A certain thickness needs to be installed depending on where you are situated. These guidelines have been set to ensure maximum energy saving in all homes throughout South Africa.
In areas where it is cold, like Johannesburg, Pretoria, and Cape Town, the 145mm and 135mm should be used. Durban and surrounds can use the 100mm.
If you are unsure as to what thickness you should be using, any installer should be able to tell you. All approved insulation installers will know the building regulations regarding insulation materials.
If you follow the climatic region guidelines, then you should be able to achieve a 4 – 8 degree difference in your residential, commercial or industrial property. This is before you add heating and cooling systems to the equation.
Source: South African Building Laws