Convention 3.07 - Appropriate Use of U and Km Values

In the absence of more specific values the library (or inference) U and Km values for the fabric constructiontype are used.

If an accurate U value or an accurate Km value is available for the specific construction from a suitablesource this should be entered to replace the corresponding library (or inference) value.

If both the U value and Km value for the specific construction are available from the same source then bothshould be entered. If not from the same source then only the U value should be used, combined with thelibrary (or inference) Km value.

The entry of defined values is only appropriate where the values have been calculated by a Level 4 qualifiedassessor or other suitably qualified and accredited person\organisation or have been taken from an ‘as built’design specification document.

Suitable qualification\accreditation is through membership of a recognised U-value calculation competencyscheme (BBA/TIMSA [UK]), OCDEA membership (England & Wales, Northern Ireland, Scotland) or anyother scheme formally agreed between Accreditation Schemes/Approved Organisations and Government.

Where U and/or Km values are entered by the assessor, a copy of the documentation stating the introducedvalues must be provided if called for audit along with evidence of the library (or inference) construction anyretained value relates to.