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 chim-
ney 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 set-
ting 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 alter-
nate 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 exteri
-
or 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 chim
-
ney, 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 51)
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 com
-
mon 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 52)
Note:
A firestop is required wherever a chimney passes be
-
tween one zone of a building to another. Ex: When the chim
-
neypasses 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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