49
DM 54 Chimney System: Offset Block (cont.)
Offset block Support Foundations:
It is required that every third Isokern offset chimney block
in the sequence be supported down to footings via concrete block or
steel support columns.
Plan replace and DM 54 chimney systems carefully before
foundations are laid to assure that proper footings are available to
support Isokern offset blocks chimney run.
To calculate the distance of Isokern offset chimney travel
in a straight line to the right, left or to the rear of the rebox/smoke
dome assembly, proceed as follows:
Refer to Figure 90: temporarily dry set a DM 54 outer casing
block in its proper location on top of the completed rebox/smoke
dome assembly as though starting a straight chimney.
If the offset sequence is to move to the left then, starting
from the right side of the temporary DM 54 outer casing measure
left ward to the far face of the overhead obstruction that needs to be
bypassed by the vertical chimney run.
For accurate measuring drop a plumb line down from the far
face of overhead obstruction to the level of the top of the smoke dome
assembly. Measure from the far side of the temporary DM 54 outer
casing to the plumb line.
This measurement, taken in inches and divided by three
(three inches of horizontal travel per offset block) gives the total num-
ber of offset blocks needed to accomplish the required travel distance.
To calculate the height that the offset block sequence will
require, take the total number of offset blocks needed to accomplish
the travel distance (described above) multiplied by 6”. This number is
the height (inches) that the offset sequence will require.
When establishing the “far face” of the overhead
obstruction, be sure that the DM 54 chimney blocks can run straight
to chimney termination without further overhead obstruction since a
second offset sequence is not allowed. (Figure 101)
Be sure that there is sufcient space beyond the “far face” of
the overhead obstruction to accept the DM 54 chimney’s outer casing
dimension of 21 1/2”.
Support all offset sequences down to bearing as previously
discussed on page 47.
FIGURE 99
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