DM 54 Chimney System: Lateral Support
CAUTION:
Maintain three inch (3”) minimum clearance to
insulation from all DM 54 chimney component surfaces.
After setting the DM 54 inner liner starter piece,
apply mortar to the top of the starter liner. Continue the straight
chimney run by placing a full height inner liner onto the six
inch (6”) starter liner. The top of this full height inner liner
will sit 6” above the top of the outer casing block that was
previously set.
This six inch (6”) offset between joints of the inner
liner stack and the joints of the outer casing stack continues to
the top of the chimney run.
Continue the straight vertical DM 54 chimney by
setting an outer casing block onto the mortared top surface of
the preceding outer casing. The grooves on the bottom end of
the upper outer casing block fit onto the tongues on the top of
the lower outer casing block. This assures proper alignment of
the two components.
Next place a full height inner liner onto the mortared
top end of the previously set inner liner. Proceed this alternate
stacking of outer casing blocks and inner liners until the
desired height of the flue is attained.
Mortar all outer casing blocks together and mortar all inner
liners together. Do not mortar the space between the outer
casing and the liner.
Lateral Support for DM 54 Chimneys:
Where the DM 54 chimney is built up along an
exterior wall the vertical chimney system should be connected
to the structural wall system at a minimum of four foot (4’)
intervals.
This connection can be made using 18 gauge strap
ties (Simpson Strong Tie CS coil strap, or equal).
Starting on one side of the DM 54 chimney, at four
foot (4’) intervals up the structural wall adjoining the chimney,
connect one 18 gauage strap tie to the structural wall with
two, three inch (3”) #8 (minimum) wood screws or masonry
anchors, as appropriate.
Next fold the strap around the three exposed sides of
the DM 54. Connect the strap to each of the three DM 54 faces
with two, one and one-half inch (1-1/2”) long masonry anchors,
such as “Tapcon” or “Titen” screws. Fasten the strap back to
the structural wall with two three inch (3”) # 8 (minimum)
wood screws or masonry screws, as appropriate. (Figure 92)
Where DM 54 chimneys are built up from the interior
walls the DM 54 chimney outer casing block is to be laterally
braced at ceiling and roof penetrations.
Pressure treated two inch (2”) by four inch (4”)
blocks, set at each side of the flue between the trusses or rafters
and fastened to the pre-engineered roof trusses or rafters with
two 16d common nails at each end, provides lateral support,
parallel with the framing.
Additionally, a two inch (2”) by four inch (4”) by six
feet (6’) minimum pressure treated member (“rat run”) installed
on each side of and butted up to the outer casing block will
provide lateral support perpendicular to the direction of the truss
or rafter framing system.
Fasten the perpendicular member with two 16d
common nails to each intersecting truss or rafter.
The perpendicular bracing should be installed on the
top side the ceiling level framing as well as on the bottom side
of the rafters. (Figure 93)
Note:
A firestop is required wherever a chimney passes between
one zone of a building to another. Ex: When the chimneypasses
through the ceiling into the attic area, there must be a sealed
area around the chimney so there isn’t a chaseway for a fire to
get to the attic.
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