Answer - The minimum required thickness of the Micore 160 is .417”, therefore round up to nearest standard thickness available which is 1/2”.

Listed Material

 

k (per inch)

r (per inch)

Listed Min.Thickness

 

 

 

 

Listed Material

.84

1.19

1"

 

KL

rL

TL

** Approved Alternate Materials for Floor/Hearth Protection

 

 

 

AlternativeMaterials

Thermal Values

MinimumThickness

 

 

 

(rounded to nearest 1/8 inch)

 

 

 

 

 

k (per inch)

r (per inch)

Min. Thickness

 

KM

rM

TM

Kaowool M Board

.47

2.13

.56" (1/2")

 

 

 

 

Micore 160™

.35

2.86

.42" (3/8")

U.S. Gypsum

 

 

 

 

 

 

 

Micore 300™

.46

2.17

.55" (1/2")

U.S. Gypsum

 

 

 

 

 

 

 

Durock™ Cement Board

1.92

.52

2.29" (2-1/4")

U.S. Gypsum

 

 

 

Hardibacker™

1.95

.513

2.32" (2-3/8")

 

 

 

 

Hardibacker 500™

2.30

.435

2.74" (2-3/4")

 

 

 

 

Cultered Stone Hearth-

2.82

.355

3.36" (3-3/8")

stone™

 

 

 

 

 

 

 

Wonderboard

3.23

.31

3.85" (3-7/8")

 

 

 

 

Super Firetemp M

.61

1.64

.73" (3/4")

Johns-Manville

 

 

 

 

 

 

 

Super Firetemp L

.54

1.85

.64" (5/8")

Johns-Manville

 

 

 

 

 

 

 

Face brick

9.00

.111

10.71" (10-3/4")

 

 

 

 

Common brick

5.00

.20

5.95" (6")

 

 

 

 

Cement mortar

5.00

.20

5.95" (6")

 

 

 

 

Ceramic tile

12.5

.08

14.88" (14-7/8")

 

 

 

 

Marble

11

.09

13.10" (13-1/8")

 

 

 

 

Table 1

 

 

 

**If the hearth extension material(s) that is intended to be used is NOT listed on Table 1, the material can still be used if the material(s) is noncombustible. However, the manufacturer of the material must provide either the listed k- value per inch or r-value per inch with listed thickness so that the minimum thickness required for the hearth can be calculated (per instructions on this Page and/or as specified in the NFI Certification manuals).

Note: Also see NFI (National Fireplace Institute) Certification Manuals showing other acceptable calculation methods and acceptable alternate materials which can be used.

NOTE: DIAGRAMS & ILLUSTRATIONS NOT TO SCALE.

40"

Wall Shield

(1016mm)

Required if

 

less than

 

18" (457mm)

40"

(1016mm)

C

B

C

A

Figure 48

Calculating Minimum Thickness if Multiple Materials are Used

At times it is important to know what combination of materials are acceptable for use as floor protection. The “R values” are used to determine acceptable combinations of materials because “R values” are additive where r and k values are not.

“R value” = 1/k = “r” x thickness of material used

Example: Given that the required “R value” for a suitable floor protector used must be equal to or greater than:

“R” = rL x TL = 1.19 x 1” = 1.19.”

If it is desired to elevate a marble hearth extension to a level of 5” or more above the floor surface. What combination of noncombustible materials can be used to accomplish this?

If common brick is used so that the 3 1/2” dimension is the height, “R” for the common brick becomes:

brick

“R”M = rM x TS = 0.20 x 3 1/2" = .70

Using 1/2” of mortar to set the brick, “R” for the mortar is calculated as follows:

mortar

“R”M = rM x TS = 0.20 x 1/2" = .10

Next, a 3/4" marble slab set in 1/2" mortar covers the brick, “R” for the marble and mortar becomes:

marble

“R”M = rM x TS = 0.05 x 3/4" = .038

mortar

“R”M = rM x TS = 0.20 x 1/2" = .10

17