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U-value Calculator for Cavity Walls

It is designed for all users, but specifically those who want to make an assessment of the U-value achieved with various combinations of block and thermal insulation prior to finalising a wall design. Users need to make a selection from each of the drop-down boxes.

In the internal finish drop-down box the R-values for the 5 options of insulating plasterboard are for plasterboard, insulation and air-gap combined. Some drop-down boxes require input from the user and others permit changes to be made:

External render
Select an option from the drop down box
External insulation
Select an option from the drop down box. If an external insulation is to be used the insulation thickness needs to be inserted.
Details about outer leaf
Select an option from the drop down box. The default values can be used or the λ-value of the blockwork can be changed if an appropriate value is available from the block manufacturer.
Details about cavity
Select an option from the drop down box. The thickness of insulation needs to be inserted. A selection of R-value of the residual cavity needs to be made (guidance available from insulation manufacturer).
Details about inner leaf
Select an option from the drop down box. Default values can be used or the λ-value of the blockwork can be changed if an appropriate value is available from the block manufacturer.
Details about internal finish
Select an option from the drop down box.

Note: Whilst the calculator is simple to use and gives results close to those achieved with a detailed U-value calculation it includes a number of assumptions such as type and density of wall ties. As a result, a calculation may not be in accordance with BS EN ISO 6946 (ie if the program assumptions do not match those of the design choices)