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When the fireplace is installed directly on the floor, a noncombustible floor protection in front
of the unit must be installed and have an R value insulation equal to or greater than 1.00. The
use of an R value is convenient when more than one material is going to be used in the hearth
extension to cover the combustible surface. This is because R values are additive, whereas K
values are not. To find the corresponding R factor to use for some selected materials, please
see Appendix section. Please note that the minimum height of the raised base of the fireplace
should match or exceed the height of the floor protection.
2.4.2.1 R Calculations
There are two ways to calculate the R factor of the floor protection. First, by adding the R-
values of the proposed materials or if some K and thickness values are given, by converting
them to R values.
To calculate the R factor for a composite floor protection made of a combination of
alternative materials, simply add the R-values of those materials. If the result is equal to or
larger than the required R value, the combination is acceptable. For R-values of some selected
materials, see Appendix section.
Example:
Required floor protection R of 1.00. Proposed materials: four inches of brick and one inch of
®
Durock
board
Four inches of brick (R = 4 x 0.2 = 0,8) plus 1 inch of Durock
This R value is larger than the required 1.00 and is therefore acceptable
In the case of a known K and thickness of alternative materials to be used in combination,
convert all K values to R by dividing the thickness of each material by its K value. Add the R
values of your proposed materials as shown in the previous example.
Example:
K value = 0.75
Thickness = 1
R value = Thickness/K = 1/0.75 = 1.33
0.8 + 0.52 = 1.32.
16
®
(R = 1 x 0.52 = 0.52).
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