Osburn 1100 MODEL INSERT Owner's Manual page 12

If a non-combustible material floor protection needs to be added in front and level with the hearth extension
masonry fireplace (see Figure 2.6a), an R factor equal to or greater than 1.00 is required. If the extension of
the masonry hearth is raised at least 4" from the floor protection (see Figure 2.6b), a non-combustible
material without an R factor is sufficient.
Figure 2.6a
Figure 2.6b
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