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# Thermal Values Explained - A quick guide to U-Values, R-Values & Lambda Values

U-Value

The coefficient of heat transmission or thermal transmittance, a U-Value is basically a measure of heat loss through a structural element. It is calculated on the rate at which heat transfers through 1 square metre of a structure, where the temperature difference between the inner and outer face is 1 degree Celsius.

U-Value (w/m²K) = the measure of structural heat loss per unit of surface area

Lambda (λ) Value Calculation

Lambda value λ(w/mK) = the value of the insulating capacity of product designed for thermal performance. Examples include Glass mineral wool Loft roll at 0.044w/mk, and Celotex GA4000 PIR board at 0.022w/mk.

The lower the value, the better the insulating capacity of the product (for a given thickness).

R-Value Calculation

The Lambda  (λ) values, combined with thickness of product, give the thermal resistance - or R value - of each element in a structure. R value is a measure of thermal resistance, measured as:

Thickness
λ

The higher the R value of any element, the better its ability to resist the transmission of heat.

Other elements included in calculation would be cavity air spaces, surface air films, and the reflective capacity of aluminium foil surfaces.

U-Value Calculation

U-Values are calculated as the reciprocal of the sum of R values, i.e.                      1
total sum of R values

The lower figure reached in calculation, the better the insulation value of the structure . ....

To discuss any technical aspects of your insulation requirements, please don't hesitate to get in touch with one of our branches,

To find out what current building regulations stipulate, please click the link here to the building regulations part of our website.

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