U-value calculations
Welcome to CAINE
CONSULTING, the specialist web-based service providing the latest Building Control 2010 Part L1A & L2A Compliance
service for all UK Domestic & Commercial Buildings. The calculation method, known as the Combined Method, is set out in
BS EN ISO 6946
What is a U-value?
A U value is a measure of heat loss in a particular building element . It is expressed in W/m2k, and details the amount of heat lost in watts (w) per square metre of material (for example wall, roof, floor etc.) when the temperature (k) outside is at least one degree lower.In a simplistic approach the lower the U- value, a low U- value usually indicates high levels of insulation. U-values are useful as it is a way of predicting the composite behavior of an entire building element rather than relying on the properties of individual materials.
U-values are important because they form the basis of any energy or carbon reduction standard. In practice, nearly every external building element has to comply with thermal standards that are expressed as a maximum U-value. Knowledge of how to simply calculate U-values at an early stage in the design process, avoids expensive re-working later on in a project. It allows the designer to test the feasibility of their project at an early stage to ensure it is fit for purpose and will comply with regulatory frameworks.
How to understand U-values?
In order to calculate U-values it is important to first understand, Thermal Conductivity, Thermal Resistance and Thermal Transmittance.
Calculating U-Values
CAINE CONSULTING, use programs to calculate U-values according to the procedures defined in:
ISO 6946:2007 (for most element types)
ISO 13370:2007 (for floors)
ISO 10077-1:2006 (for windows)
BRE Digest 465 (for steel framed elements)
BRE IP 10/02 (for Z-spacer elements)
SCI Technical Information Sheet P312 (for rail-and-bracket elements)
CAINE CONSULTING deal with most construction elements, excepting construction elements in which metal fully or partly penetrates insulation, which have to be assessed by finite element analysis. Light steel frame construction and built-up walls and roofs using rails-and-brackets or Z-spacers can also be assessed
What is a U-value?
A U value is a measure of heat loss in a particular building element . It is expressed in W/m2k, and details the amount of heat lost in watts (w) per square metre of material (for example wall, roof, floor etc.) when the temperature (k) outside is at least one degree lower.In a simplistic approach the lower the U- value, a low U- value usually indicates high levels of insulation. U-values are useful as it is a way of predicting the composite behavior of an entire building element rather than relying on the properties of individual materials.
U-values are important because they form the basis of any energy or carbon reduction standard. In practice, nearly every external building element has to comply with thermal standards that are expressed as a maximum U-value. Knowledge of how to simply calculate U-values at an early stage in the design process, avoids expensive re-working later on in a project. It allows the designer to test the feasibility of their project at an early stage to ensure it is fit for purpose and will comply with regulatory frameworks.
How to understand U-values?
In order to calculate U-values it is important to first understand, Thermal Conductivity, Thermal Resistance and Thermal Transmittance.
Lambda (Thermal Conductivity) Thermal conductivity is the rate at which heat is transmitted through a material, measured in watts per square metre of surface area for a temperature gradient of one Kelvin per metre thickness - simplified to W/mK. The Lower the value, the better the thermal efficiency of the material.
Conductivity values for common building materials can be obtained from the Chartered Institution of Building Services Engineers (CIBSE) Guide A Section 3 or from BS EN 12524: 2000 (to be replaced by BS EN ISO 10456). For specific insulation products, however, data should be obtained from manufacturers.
R-Value (Thermal Resistance) Thermal resistance is measured in m2K/W and is equal to the thickness of the material (in metres) divided by the conductivity of that material. The resistances of each material within an element are added together to determine the overall resistance of the element. The higher the R-value, the more efficient the insulation.
U-Value (Thermal Transmittance) Thermal transmittance, commonly known as the U-value, is a measure of the rate of heat loss of a building component. It is expressed as watts per square metre, per degree Kelvin, W/m2K. The U-value is calculated from the reciprocal of the combined thermal resistances of the materials in the element, air spaces
Calculating U-Values
CAINE CONSULTING, use programs to calculate U-values according to the procedures defined in:
ISO 6946:2007 (for most element types)
ISO 13370:2007 (for floors)
ISO 10077-1:2006 (for windows)
BRE Digest 465 (for steel framed elements)
BRE IP 10/02 (for Z-spacer elements)
SCI Technical Information Sheet P312 (for rail-and-bracket elements)
CAINE CONSULTING deal with most construction elements, excepting construction elements in which metal fully or partly penetrates insulation, which have to be assessed by finite element analysis. Light steel frame construction and built-up walls and roofs using rails-and-brackets or Z-spacers can also be assessed
'The Way Forward'
We would
be delighted to guide and support you through the process.
For further information regarding any of the above consultancy service please contact the office on
+44 (0) 1900 61479 or by E Mail to info@caineconsulting.co.uk