Insitu formed products - Lambda 90:90 – new Harmonised European Norm

Following the approval of a new Harmonised European Standard, EN 14064, for Insitu Formed Mineral Wool, Knauf Insulation has announced that the thermal conductivity value of its blown mineral wool products will be declared with a 90:90 statistical analysis, which will be compulsory from December 2011, and warns of possible market distortion if product comparisons are not now undertaken on a ‘like for like’ basis.

Insitu formed insulation products are those that are installed by being blown or pumped into lofts, masonry walls or framed constructions; as opposed to products supplied pre-formed in slabs, rolls or boards. The purpose of the new Harmonised European Standard is to provide statistical analysis that ensures that any thermal conductivities used in calculations are achieved most of the time in practical situations.

It is expected that the 90:90 analysis will result in a higher thermal conductivity values being calculated for mineral wool products. Currently the average (or λmean) value of measurements is used as the declared value, and because the new method relates to the value (λ90/90) that can be obtained for 90% of production within a 90% confidence level, it will result in an estimated increase (worsening) in declared thermal conductivity value of approximately 10% for existing blown mineral wool products used in cavity insulation if no adjustments are made to the product.

Knauf Insulation warns that future specification will therefore need to be carefully considered to ensure that product comparisons for this application are undertaken on a like for like basis.

In particular, as no such standard is yet available for Insitu Formed EPS Bead Insulation which also currently declares thermal conductivity as a λmean value there is a potential for market distortion. The British Board of Agrément has confirmed that, in order to avoid market distortion, it will require a similar treatment for other insitu formed products used in the same application. It would be expected that a similar or greater increase would apply to blown EPS bead products, both plain and graphite.

Stephen Wise, Technical Development Manager at Knauf Insulation said:  “The company welcomes the introduction of a Europe-wide standard, which will eventually aid product specification - once applied across all insulation types.  Whereas it is recognised that this does increase the thermal conductivity value for insitu formed mineral wool, Knauf Insulation is confident that this can be offset by varying the installed density and product characteristics of its blown mineral wool products. Indeed if the market demands, it will be possible to provide products with lower thermal conductivity than is currently supplied, using existing blowing machinery.”

It is not apparent that manufacturers of EPS bead products have a similar range of options available to enable them to improve their product and maintain its declared thermal conductivity value after a 90:90 statistical analysis is applied.

For further information on the differences between λ90/90 and λmean see BBA reference sheet 40/10 ( which states that the λ90/90 value and λmean value cannot be compared.

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