How is U-Value measured?
Calculating a U-Value is actually quite simple. The U-value can be calculated by finding the reciprocal of the sum of the thermal resistances of each material making up the building element in question. Note that, as well as the material resistances, the internal and external faces also have resistances, which must be added. These are fixed values.
U-Values are measured in watts per square metre per Kelvin
or shortened to (W/m²K)
Nearly all manufacturers of Roof Windows
and Rooflights will be able to give you U-Values of their products. One way a manufacture will test their product is in a "Hot Box". This is a machine that can test how well an insulator their product is by exposing the product to hot and cold elements, like it would in your home. (Inside your home is warm, outside is cold.)
The image on the right here is an example of how this works.
So, lets take an example! Let's say that a Double Skin Polycarbonate Roof Dome
has a U-Value of 2.8W/m²K... for every degree difference in temperature between the inside and outside of the glazing, 2.8 watts will be transmitted every square metre.
But lets also take a Double Glazed Flat Glass Rooflight
. The Glazing in this kind of Rooflight may have a Gas Filled Cavity, usually Argon, which gives better insulation. So, let's say for example the U-Value is 1.1W/m²K. For every degree difference in temperature between the inside and outside of the glazing, 1.1 watts will be transmitted every square metre. So less heat loss.
Lower the U-Value, less heat is transmitted, or lost, through the glazing.
Making Sense?Shop Low U-Value Roof Windows Shop Low U-Value Flat Glass Rooflights