Jump to navigation
Serving Alberta's Roofing Industry Since 1961
MB Section 8: Sheet Metal Flashings
Sheet metal flashings shall continuously cover
non-granular surfaced S.B.S. membrane flashing cap sheets installed
at horizontal to vertical roof junctions. Sheet metal flashings
shall be installed as soon as practical to protect the membrane
flashing from damage.
Sheet metal flashings shall be corrosion
resistant. The metal finish is not warranted by ARCA Warranty Ltd.
Protect the metal finish from damage during shipping and
Oil canning of sheet metal flashing is a natural
phenomenon and is not cause for rejection. Severity of oil canning
can be reduced by one or more of the following means:
Use a heavy gauge metal that is more rigid
Use metal with low-gloss finish or textured by embossing or
striations to reduce visual effects
When the face exceeds 250mm (10"), fabricate flashings in two
pieces or use stiffening ribs, v-groove, or cross break.
MB-8.2 Weights and Thickness
The weight and thickness limits shown in the
following table shall be followed within the CSA tolerances
designated for the metal type shown and does not include the metal
finish. The minimum weight or thickness of the sheet metal flashing
shown in the table must be increased to the next heavier dimension
when the unfastened vertical length of the sheet metal exceeds
457mm (18”), when measured from its main anchorage point.
||0.020 - 0.022
||0.50 - 0.56
||0.030 - 0.034
||0.76 - 0.87
Exposed sheet metal edges shall be hemmed and
shall not be left raw cut with the exception of field fabricated
joints found at corners. The top edge of the base flashing need not
be hemmed when covered by a cap flashing. Individual sheet metal
flashing pieces shall not exceed 3000mm (10 ft.) in length (Also
Except for drip edge flashings with lapped end
joints, the ends of the metal flashings shall be joined by S-locks
or standing seams. S-lock flashing ends shall be fabricated to
permit an approximate 25mm (1”) insert, with a tolerance of
± 6.4mm (1/4”), in addition to an allowance for the
thermal movement of the sheet metal flashings.
Standing seams shall extend a minimum distance
of 25mm (1”) above the flashing surface and shall incorporate
a single lock fold.
The horizontal seams at corners shall be joined
with a double seam or a standing seam.
Vertical corner seams may be lapped and mitered
when not joined with a standing seam.
No soldering or caulking of joints is necessary
except where a watertight joint is required at miscellaneous sheet
metal flashing joints and where horizontal flanges attach to
MB-8.4 Wall Flashings
MB-8.4.1 Base Flashings
A sheet metal base flashing need not cover
granular surfaced modified bitumen membrane flashing cap sheets
except where required by the building code.
A two (2) piece sheet metal wall flashing shall
fully cover non-granular surfaced modified bitumen flashing
When required, sheet metal base flashings shall
be mechanically fastened to solid backing, at intervals not
exceeding 1500mm (5 ft.) centers, with approved fasteners placed
approximately 175mm (7”) above the primary membrane.
MB-8.4.2 Cap Flashings
Where cap flashing is required, the top of walls
shall be covered with wood blocking capable of providing sufficient
holding force to anchor nail and screw fasten cap flashings. Where
membrane flashing does not cover the blocking, a water proofing
membrane shall cover the blocking and extend down each side a
minimum distance of 50mm (2").
Cap flashings shall completely cover the wood
blocking and shall in corporate a minimum 50mm (2") wide vertical
face, excluding the drip edge.
The vertical flashing face shall overlap the
wall finish and incorporate a drip edge to shed water.
Cap flashings shall be concealed fastened at one
end with galvanized roofing nails placed in both the horizontal and
vertical faces of the S-lock end joint.
On vertical faces the cap flashing shall be
mechanically fastened to the blocking with wood screws placed at
maximum 1500mm (5 ft.) centres.
Mid-fastening of cap flashing lengths with
screws may be substituted with sheet metal hook strips. Sheet metal
hook strips may be substituted for the wood screws. Hook strips
shall be a minimum of 1/3 the length of individual cap flashing
pieces which are greater than 1500mm (5 ft.) in length. The metal
hook strip shall be a minimum of 24 gauge, fastened at maximum
300mm (12”) on centre into the vertical face of continuous
wood blocking. Nails shall be placed a maximum 25mm (1”)
above the hook strip bottom kick-out and shall be spiral or ring
shanked. The hemmed drip edge shall be fully engaged with the hook
strip. High wind areas require special consideration determined by
the design professional.
MB-8.4.3 Counter Flashings
For smooth surfaced walls, membrane flashing
terminations shall be covered with a reglet or kick-out style
counter flashing detail.
Counter flashings shall be fabricated with a
drip along their lower edges to shed water. When sheet metal base
flashings are used, counter flashings shall overlap base flashings
a minimum distance of 50mm (2”).
Counter flashings shall not exceed 100mm
(4”) in width, excluding the drip.
For reglet style counter flashings, the wall
reglet shall be straight, of uniform width ranging between 12.7mm
(1/2”) and 19.0mm (3/4”) wide and not less than 19.0mm
(3/4”) deep. The sheet metal counter flashing shall be
mechanically fastened in the reglet at maximum 600mm (2 ft.)
centres and the exposed reglet opening continuously caulked.
Where use of a reglet is impractical, a kick-out
style counter flashing may be used for smooth surfaced substrates.
Kick-out style counter flashings shall be mechanically fastened to
the wall at maximum 600mm (2 ft.) centers. Fasteners shall be
placed immediately below the kick-out. A continuous metal bar may
be incorporated to ensure wall contact is maintained. The kick-out
lip shall be continuously caulked with a compatible sealant tooled
to shed water.
MB-8.5 Roof Edge Flashings
A metal flashing is required to finish, shed
water and protect the modified bituminous roof membranes at roof
The roof edge may be finished with a cant edge
detail, parapet flashings or a drip edge flashing detail.
Exposed fasteners are not permitted in the cant
area or on horizontal/top flashing surfaces.
MB-8.5.2 Cant Edge Flashing
Where cant edge flashing is required, it shall
be joined by S-lock end joints and concealed fastened to the
exterior face of the wood cant strip with galvanized roofing nails
placed in end joint flanges.
MB-8.5.3 Parapet Flashing
Where parapet cap flashings are required, the
top of the parapet shall be covered with wood blocking capable of
providing sufficient holding force to anchor nail and screw fasten
Parapet cap flashings shall be fabricated to
completely cover the membrane flashing over the blocking and
incorporate a minimum vertical face dimension of 50mm (2”),
excluding the drip edge. The exterior vertical flashing face shall
overlap the completed wall finish.
Parapet flashings shall be concealed fastened at
one end using galvanized roofing nails placed in both the
horizontal and vertical faces of the S-lock end joint.
Additionally, the exterior cap flashing face shall be mechanically
fastened to the blocking with wood screws placed at intervals not
exceeding 1500mm (5 ft.) centers. Sheet metal hook strips, fastened
to the blocking, may be substituted for the wood screws (see
When the parapet width (girth) exceeds 400mm
(16”), the maximum length of cap flashing piece shall be
1500mm (5 ft.).
MB-8.5.4 Drip Edge Flashing
Where parapet cap flashings are not required, a
granular surfaced modified bitumen flashing membrane may be
terminated to a continuous metal drip edge flashing attached at the
exterior top surface of the parapet or a structural deck's
perimeter wood blocking.
Drip edge flashings shall be fabricated with
horizontal flanges between 100mm (4”) and 125mm (5”)
wide. The fascia flange shall not exceed 100mm (4”) in width
on the vertical surface, excluding the drip.
For non-nailable substrates, continuous wood
blocking shall be fastened to the structure for the attachment of
the metal drip edge flashing. Prior to fastening, the horizontal
flange shall be set in a continuous bed of a compatible sealant,
applied at the approximate rate of 2.5 kg/m² (0.5
lbs./ft.²), placed over the membrane. The horizontal flange
shall be mechanically fastened to the blocking with fasteners
staggered front to back at maximum 200mm (8”) centers. Drip
edge flashings shall be joined with minimum 100mm (4”) wide
end laps. The top surface of the horizontal flange shall be primed
with a compatible primer to ensure proper adhesion of the flashing
MB-8.6 Control Joint Flashings
When a roof area divider is fully covered by a
granular surfaced membrane flashing cap sheet, a sheet metal
flashing is not required.
Roof expansion joints require a sheet metal cap
flashing regardless of the membrane flashing cap sheet
MB-8.7 Scupper Drains
Sheet metal scupper drains shall be sized to
extend beyond the exterior wall finish and to provide for minimum
100mm (4") wide base and wall flanges formed at the interior face
of the scupper drain opening.
Through wall type scuppers must be four (4)
sided with the upper scupper opening surface covered with sheet
Where control of drainage is required, the
scupper assembly may include an external hopper and an attached
MB-8.8 Miscellaneous Sheet Metal
Miscellaneous sheet metal flashings for roof
jacks, gum boxes, ventilators, goosenecks and scupper penetrations
shall be watertight, incorporate a continuous one piece deck
flange, with no open corners, using a double seam or approved lock
to secure the deck flange to the vertical flashing body.
Deck flanges shall not be fabricated less than
100mm (4”) nor more than 200mm (8”) in width.
Watertight sheet metal flashing joints shall be
soldered or welded.
Watertight aluminum flashing joints must be
When approved, specialty flashings may be
substituted for fabricated sheet metal flashings.
© 2016 Alberta Roofing Contractors Association