R-value

The charts below show the difference in r-values between think pink aerolite and isotherm ceiling insulation. People often ask us which ceiling insulation the the better of the two (aerolite vs isotherm). While both have their pros and cons, the graphs below show the r-values of the products for you to make your own educated decision on which insulation best suits your needs. Isotherm have just launched a new range of product thickness’s with increased density in their new ceiling insulation range.

Isotherm vs Aerolite R-value charts

isotherm-r-value-tableaerolite-r-value-table

What exactly is the R-value?

The R-value – Thermal Resistance is a direct indication of the performance of the product.  The higher it is, the better the insulating effect the insulation will have. It is determined in the following way:

R-value = Thickness (of the material) / Its Thermal Conductivity (or K-value)

The thickness is determined by the manufacturer – and will normally form part of the product range.  The K-value is determined in an accredited laboratory.  The manufacturer will produce a sample that is manufactured at a stated density (weight) and will submit to the laboratory for testing.  The idea is to achieve an as low as possible K-value, in other words, a low thermal conductivity – put plainly, the product must be a bad conductor of heat flow.

Once the K-value is determined, the R-value can be calculated, for example:

For a 50mm thick blanket with tested K-value of 0.046:

0.05 (thickness) / 0.046 (k-value)  = 1.08 (R-value)

As long as the manufacturer manufactures the other thicknesses in his range at the same density than the submitted sample, he can use the same formula and k-value to determine the R-values, eg:

For a 100mm thick blanket:

0.1 (thickness) / 0.046 (tested k-value)= 2.17 (R-value)

This is where the consumer must be vigilant – some dubious manufacturers may reduce the density or weight of their products to save on raw material.  If they do this, they cannot use the tested k-value and thus cannot claim a good R-value.  Always demand to see the test report and stated density that the manufacturer uses to determine R-values.

The R-value determined in the examples above is the so-called Product R-Value.  The fact is however that the roof tiles and ceiling (as well as other roofing materials) also contribute to the insulating effect.  In practice, the Total R-value of both roofing material and insulation material must thus be considered.  So, if the insulation material’s R-value is 2.17, and the roof and ceiling materials have a R-value of 0.53, then the Total R-value will be 2.7.  Refer to The Thermal Insulation Association of South Africa (TIASA) website for guidelines on Total R-values.

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