What are U-values, R-values and lambda values?

5 October 2016 Kingspan Insulation UK

An introduction to lambda values, R-values and U-values

If you’re new to the industry, you’ll soon discover that the word ‘value’ is thrown around like there’s no tomorrow. More often than not, this ‘value’ is accompanied by a letter – which can lead to all sorts of confusion.

What is a lambda value?

The lambda value, also portrayed as ‘K-value’ or ‘λ-value’, measures a product’s thermal conductivity in units of W/m·K.

A good insulation will have as low a lambda value as possible to reduce heat loss. For example, our new lower lambda products each have a lambda value of 0.018 W/m·K across all thicknesses.

What about an R-value?

A product’s R-value measures its thermal resistance in units of m²·K/W.

By dividing a material’s thickness (in metres) by its lambda value, you can discover how well it resists heat transfer at a specific thickness.

The best insulation will have a high R-value at a low thickness, indicating that it is just as good at reducing heat loss as its thicker counterparts.

So, what is a U-value?

A U-value is a sum of the thermal resistances of the layers that make up an entire building element – for example, a roof, wall or floor. It also includes adjustments for any fixings or air gaps.

A U-value value shows, in units of W/m²·K, the ability of an element to transmit heat from a warm space to a cold space in a building, and vice versa. The lower the U-value, the better insulated the building element.

A building element’s U-value is extremely important as there are certain standards that should be reached according to Building Regulations / Standards.

Have a play with our free U-value Calculator, which demonstrates how you need information on each aspect of a building element to get an accurate U-value.

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