DM Chimney System: Lateral Support
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 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 t 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 ue is attained. Mortar all outer casing blocks
together and mortar all inner liners together. Do not mortar or
ll the space between the outer casing and the inner liner.
Lateral Support for DM Chimneys:
Though not required, it is recommended that where
the DM chimney is built up along an exterior wall the vertical
chimney system can 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 equivalent).
Starting on one side of the DM 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 outer casing. Connect the strap to each of the three outer
casing 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 50)
Where DM chimneys are built up from the interior
walls the DM 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 ue 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 51)
Note: A restop is required wherever a chimney passes between
one zone of a building to another. Ex: When the chimney passes
through the ceiling into the attic area, there must be a sealed
area around the chimney so there isn’t a chaseway for a re to
get to the attic.
33
FIGURE 50
FIGURE 51
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