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MB Section 8: Sheet Metal Flashings

MB-8.1 General

.1

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.

.2

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 handling.

.3

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

.1

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.
Minimum Maximum
Metal Gauge Inches mm Gauge Inches mm
Aluminum 22 0.021 0.53 16 0.044 1.12
Copper 16 oz. 20 oz.
Coated Steel 26 0.020 - 0.022 0.50 - 0.56 22 0.030 - 0.034 0.76 - 0.87
Stainless Steel 28 0.014 0.36 22 0.027 .69

MB-8.3 Fabrication

.1

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 see 8.5.3.4).

.2

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.

.3

Standing seams shall extend a minimum distance of 25mm (1”) above the flashing surface and shall incorporate a single lock fold.

.4

The horizontal seams at corners shall be joined with a double seam or a standing seam.

.5

Vertical corner seams may be lapped and mitered when not joined with a standing seam.

.6

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 vertical flashings.

MB-8.4 Wall Flashings

MB-8.4.1 Base Flashings

.1

A sheet metal base flashing need not cover granular surfaced modified bitumen membrane flashing cap sheets except where required by the building code.

.2

A two (2) piece sheet metal wall flashing shall fully cover non-granular surfaced modified bitumen flashing membranes.

.3

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

.1

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").

.2

Cap flashings shall completely cover the wood blocking and shall in corporate a minimum 50mm (2") wide vertical face, excluding the drip edge.

.3

The vertical flashing face shall overlap the wall finish and incorporate a drip edge to shed water.

.4

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.

.5

On vertical faces the cap flashing shall be mechanically fastened to the blocking with wood screws placed at maximum 1500mm (5 ft.) centres.

.6

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

.1

For smooth surfaced walls, membrane flashing terminations shall be covered with a reglet or kick-out style counter flashing detail.

.2

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”).

.3

Counter flashings shall not exceed 100mm (4”) in width, excluding the drip.

.4

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.

.5

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

MB-8.5.1 General

.1

A metal flashing is required to finish, shed water and protect the modified bituminous roof membranes at roof edges.

.2

The roof edge may be finished with a cant edge detail, parapet flashings or a drip edge flashing detail.

.3

Exposed fasteners are not permitted in the cant area or on horizontal/top flashing surfaces.

MB-8.5.2 Cant Edge Flashing

.1

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

.1

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 flashings.

.2

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.

.3

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 8.4.2.6).

.4

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

.1

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.

.2

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.

.3

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 membranes.

MB-8.6 Control Joint Flashings

.1

When a roof area divider is fully covered by a granular surfaced membrane flashing cap sheet, a sheet metal flashing is not required.

.2

Roof expansion joints require a sheet metal cap flashing regardless of the membrane flashing cap sheet surface.

MB-8.7 Scupper Drains

.1

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.

.2

Through wall type scuppers must be four (4) sided with the upper scupper opening surface covered with sheet metal.

.3

Where control of drainage is required, the scupper assembly may include an external hopper and an attached downpipe.

MB-8.8 Miscellaneous Sheet Metal Flashings

.1

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.

.2

Deck flanges shall not be fabricated less than 100mm (4”) nor more than 200mm (8”) in width.

.3

Watertight sheet metal flashing joints shall be soldered or welded.

.4

Watertight aluminum flashing joints must be welded.

.5

When approved, specialty flashings may be substituted for fabricated sheet metal flashings.