U-Value Calculations What is a U-Value?Well to put it simply, a U-Value is the measurement of the rate of heat loss through a material. Which means that in all aspects of home design one should strive for the lowest U-Values possible because the lower the U-Value, the less heat will be needlessly escaping. The calculation of U-Values can be quite complex as it is measured as the amount of heat loss through a 1 square metre of material for every degree difference in temperature either side of the material. It is indicated in units of watts per square metre per degree Kelvin or W/m2 K. Kelvin is used as the scale of temperature difference, but this is numerically equal to degrees celsius.
U-Values for Building Regulations 2010The elements of a house are the roof, external wall, party wall, floor and windows/doors. These values can be lowered in order to improve the insulation qualities of the home.
The limiting U-Values have changed with the building regulations 2010:
Worst Area Weighted U-Values Permitted
2006 2010 Roof 0.25 0.2 External Wall 0.35 0.3 *Party Wall N/A 0.2 Floor 0.25 0.25 Windows 2.2 2.0 Air Permeability 10.0 10.0
*Note the introduction of the party wall element. The party wall U-Value depends on construction:
Party Wall Construction Solid 0.0 Unfilled no Edge Sealing 0.5 Unfilled with Edge Sealing 0.2 Fully filled + Edge Sealing 0.0
Sealing must be in line with insulation in adjacent elements (e.g. in line with loft insulation). This also applies to timber frame walls too but a timber framed dwelling with insulated panels on both sides of an unfilled cavity may be allowed to have a U-Value of 0.2.
Government approved software is used by Premier Assessors Consultancy to calculate the U-Value of an element. The specific construction of the element must be accurately submitted to HIS and if an improvement is required Premier Assessors can advise the client on possible solutions.