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Calculate R-Value (SABS SANS10400XA)

This Excel spreadsheet will allow you to calculate your R Value.

To comply with the SABS recent SANS 10400 XA regulations, the building control officer will require the architect/developer to provide a calculation to prove that the R-Value for a plastered cavity wall meets/exceeds the requirement of 0.35. Use this spreadsheet to show your calculations.


The R-value is a measure of thermal resistance used in the building and construction industry. Under uniform conditions it is the ratio of the temperature difference across an insulator and the heat flux (heat transfer per unit area, ) through it.

Designed for Excel 2010. There is limited ‘backward compatibility’ with other Excel versions. The spreadsheet is protected, you can only enter data into the specific input blocks. Please "Enable Editing" if your version of Excel is secure to be able to input your own data.

Clay bricks natural propensity to equalize internal temperatures through the day and night thereby reducing the need for artificial heating or cooling that extends to a reduced need for electrical energy for the heating and cooling of habitable space, this affording considerable benefits both in terms of cost containment to the home owner and reduced impact on our natural environment.

How is a material's R-Value & CR-Value calculated?

The R-value being discussed is the unit thermal resistance. This is used for a unit value of any particular material. It is expressed as the thickness of the material divided by the thermal conductivity. For the thermal resistance of an entire section of material, instead of the unit resistance, divide the unit thermal resistance by the area of the material. For example, if you have the unit thermal resistance of a wall, divide by the cross-sectional area of the depth of the wall to compute the thermal resistance.

The unit thermal conductance of a material is denoted as C and is the reciprocal of the unit thermal resistance. This can also be called the unit surface conductance and denoted by h. The higher the number, the better the building insulation's effectiveness. (R value is 1/h.) R-value is the reciprocal of U-value.

Author  Howard Harris

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