Houses need protection from the elements, such as wind driven rain, frost, snow, fog, pollution and so on. The exterior of our house is very important to be kept in good condition. EWI will retain any heat in the house, and thus means that you will save money on heating bills and the heat will not escape. The thickness of thermal insulation must be at least 10 to 15 centimetres (3.9 to 5.9 in). External wall insulation systems generally comprise an insulation layer to achieve the requisite thermal performance protected with a weatherproof finish, usually a render, although brick slips, tiles, and decorative boards can also be used.