HOW DO YOU CALCULATE A U-VALUE?
In a sentence: u-values are calculated by finding the reciprocal of the sum of the thermal resistances of our target component.
This might sound complex, but the calculation is quite straightforward. Thermal resistance (also known as the R-value) is simply a measure of the heat insulation capacity of a material. It’s how much heat is kept in across its thickness (as opposed to U value – which is how much it loses per degree C.)
R-values can be calculated as R = t/k , where t is the thickness, in metres, of the material in question, and k is the conductivity (sometimes referred to as the k-value). You can look up the k-values of common materials online.
Finding your U-value, then, is a case of adding together the thermal resistances (the R-values) of each building material of the unit we want – say, perhaps, one of our beautifully insulated, high performance windows - then dividing 1 by this number.
Your final U-value calculation might be dependent on the R-values of one or two component parts; it could comprise of a list of many different values. Sometimes, we look separately at the U-values for different parts of our windows for a more technical overview.
WHAT ABOUT PASSIVE HOUSE REQUIREMENTS?
The International Passive House Association describes the Passive House Standard as “the only internationally recognised, performance-based energy standard in construction”. To become Passive House certified, a new building must meet strict requirements
in its thermal insulation, windows, ventilation heat recovery, airtightness and thermal bridging control specification. The end goal is to create a comfortable, affordable and impressively low-energy building.
For a window to meet Passive House requirements, the entire unit, i.e. glazing and frame, should have a U-value of 0.80W/(m²K) or less – a specification easily met by most of our triple-glazed range.