U-value Calculations measure the speed or rate of heat transfer through individual elements of a building’s fabric. The thermal properties of each of the materials are added together using software approved by the Building Research Establishment.
The rate of heat loss through the individual element (wall, floor or roof) is quantified as a U-value. Lower U-values represent a better insulated construction and lower rate of heat loss.
Very broadly, the better (i.e. lower) the U-value of a building’s fabric, the less energy is required to maintain comfortable conditions inside the building.
When are U-value Calculation required?
Sometimes U-value calculations are required by Building Control bodies for certain developments such as extensions. This might be to prove the rate of heat loss, but can also be to show that condensation is unlikely to occur within the structure.
U-Value Calculations and Extensions
There are several ways in which an extension to a property can show compliance with the energy requirements of Building Regulations.
Normally Glazed extensions
Individual U-value calculations can be used to show compliance for new extensions, were opening area by showing that the elements are at least as good the maximum allowable U-values for the building elements.
Highly Glazed extensions
Another method of showing compliance, where the glazing exceeds the prescribed area, is the Area Weighted U-value approach. This approach allows lower U-values on one part of the extension to be compensated for by a higher U-value elsewhere in the structure.
An alternative to this would be to carry out a Whole Dwelling SAP calculation.
Our assessor has provided advice on construction and insulation of properties for over 25 years and has taught Uvalue calculation and other aspects of thermal performance for many years.
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