Flashing, Copings, and Sheet Metal Details

Chapter Introduction

Chapter 7 of the Interprovincial Red Seal program for the roofing trade covers flashing, copings, and sheet metal details. These components form the critical interface between the roofing system and other building components. Failure in these areas represents the most frequent cause of water infiltration, even when the roof field is perfectly executed. This chapter covers design principles, installation methods, development calculations, regulatory requirements, and common pitfalls associated with these sheet metal components.

Role and Functions of Flashing and Copings

Essential Definitions

Flashing is a piece of sheet metal or other impermeable material installed at the junction between the roof and a vertical element (wall, parapet, chimney, skylight) or between two roof planes, to direct water downward and away from the building. A coping (or cap) is the metal piece that covers the top of a parapet, wall, or chimney to protect it from the weather and prevent water from penetrating from above.

Flashing falls into two main categories:

Type	Function	Example Location
Base flashing	Waterproofing at the roof/wall junction	Base of a parapet, chimney
Cap flashing (counter-flashing)	Covers the base flashing and is embedded into the wall	Brick, concrete, or block wall

Fundamental Physical Principles

Water follows gravity and capillary tension. Every sheet metal detail must respect three principles:

11.The overlap principle: each piece must overlap the piece below it by at least 100 mm (4 in) in the direction of water flow. This minimum overlap is a common requirement of Canadian standards.

12.The drainage principle: any horizontal or nearly horizontal surface must have a minimum slope of 1:50 (2%) toward the exterior or toward the outlet.

13.The capillary barrier principle: to prevent capillary rise of water between two surfaces, you must provide a gap, a break, or a sealant.

Materials and Properties

Galvanized Steel Sheet

Galvanized steel (hot-dip) is the most common material for flashing and copings. The reference standard is CSA G164 (galvanized steel sheet). The recommended minimum thickness for flashing is 0.46 mm (28 gauge) for residential applications and 0.61 mm (24 gauge) for commercial and industrial applications.

Copper

Copper offers exceptional service life (over 100 years) and develops a characteristic green patina. It requires specific techniques: tin soldering, fastening with copper fasteners (never steel, to avoid galvanic corrosion). Common thicknesses: 0.40 mm to 0.60 mm.

Aluminum

Aluminum is lightweight, corrosion-resistant, and easy to form. It must never be in direct contact with copper or galvanized steel (galvanic corrosion). Minimum thickness: 0.61 mm (24 gauge).

Stainless Steel

Used in corrosive environments (industrial areas, seaside) or for high-value roofing. Stainless steel type 304 or 316 is recommended. It is more difficult to form and more costly.

Material Comparison

Material	Estimated Service Life	Corrosion Resistance	Ease of Forming	Relative Cost
Galvanized steel	20-40 years	Good	Good	Low
Aluminum	40-60 years	Very good	Excellent	Medium
Copper	80-100+ years	Excellent	Good	High
Stainless steel	100+ years	Excellent	Difficult	Very high

Development and Calculation of Sheet Metal Pieces

Calculating Flashing Development

Development is the total width of the sheet metal strip needed to fabricate a piece, accounting for all bends and returns. The general formula is:

Development = Σ (length of each segment) − (correction factor for each bend)

For a 90° bend in sheet metal of thickness t, the bend allowance loss is approximately 2t. For a 180° bend (return), the loss is 4t.

Calculation example: Base flashing with a horizontal leg of 100 mm, a vertical leg of 150 mm, and a return of 20 mm. Sheet thickness: 0.61 mm.

Segment 1 (horizontal): 100 mm

Segment 2 (vertical): 150 mm

Segment 3 (return): 20 mm

Gross total: 270 mm

Bend 1 (90°): − 2 × 0.61 = − 1.22 mm

Bend 2 (90°): − 2 × 0.61 = − 1.22 mm

Net development: 270 − 2.44 = 267.56 mm

Calculating Overlap Lengths

The longitudinal overlap between two flashing pieces must be at least 100 mm. For copings, the minimum overlap is 75 mm in the direction of slope. These values are absolute minimums; in regions with heavy rain or high winds, these overlaps are increased.

Calculating Slope and Drainage

The minimum slope of a coping is 1:50 (2%). To calculate the height difference Δh over a width L:

Δh = L × 0.02

Example: A coping 300 mm wide must have a height difference of 300 × 0.02 = 6 mm between the high edge and the low edge.

Base Flashing and Cap Flashing

Base Flashing (Starting Flashing)

Base flashing is installed at the junction between the roof membrane and the vertical element. It must:

Extend at least 150 mm (6 in) above the finished roof surface.

Extend horizontally at least 100 mm (4 in) onto the roof surface.

Be mechanically fastened to the vertical element at intervals not exceeding 300 mm (12 in).

Be covered by the roof membrane on its horizontal portion.

Cap Flashing (Counter-flashing)

Counter-flashing is installed over the base flashing and is embedded into the wall. It must:

Overlap the base flashing by at least 100 mm.

Be embedded into the mortar joint (masonry) at least 25 mm, or into a reglet cut into the concrete.

Be sealed with a compatible polyurethane or butyl sealant.

Allow water to drain to the exterior.

Typical Installation Procedure

58.Preparation: Clean the surface, verify that the roof membrane is in place and properly adhered.

59.Base flashing installation: Form the piece, apply it against the vertical element, fasten it mechanically.

60.Sealant application: Apply a continuous bead of sealant along the top edge.

61.Counter-flashing installation: Insert the top portion into the reglet or joint, fasten and seal.

62.Verification: Ensure all overlaps are compliant and that water can flow freely.

Parapet and Wall Copings

Coping Design

A parapet coping must include:

A minimum slope of 1:50 toward the roof side (or toward the exterior depending on configuration).

A drip edge at each lower edge to prevent water from migrating back up by capillary action.

Vertical returns of at least 25 mm on the sides.

Expansion joints every 6 m maximum for galvanized steel and every 3 m for aluminum.

Concealed or exposed fasteners with watertight washers.

One-Piece vs Two-Piece Coping

Characteristic	One-Piece	Two-Piece
Installation	Faster	Longer
Leak risk	Higher (through-fasteners)	Lower (concealed fasteners)
Cost	Lower	Higher
Durability	Good	Excellent
Recommendation	Residential	Commercial/industrial

Coping Fastening

Copings must be fastened using:

Self-tapping screws with neoprene washers (galvanized steel).

Stainless steel fasteners for copper.

Fastening clips spaced at 400 mm maximum.

Through-fasteners should be avoided where possible. If unavoidable, they must be spaced at 600 mm maximum and sealed with a compatible sealant.

Chimney and Skylight Flashing

Chimney Flashing

The chimney is a particularly vulnerable element. The flashing must consist of four distinct parts:

82.Lower flashing (low side): Installed under the roof membrane, sloping toward the roof.

83.Side flashing: Step flashing for masonry, with each piece overlapping the previous one.

84.Upper flashing (high side): Installed over the roof membrane, with an overlap of at least 100 mm.

85.Counter-flashing: Embedded into the mortar joints on the three upper and side faces.

Skylight Flashing

The skylight (or roof window) requires what is known as a "continuous base flashing" that forms a complete frame around the opening. Corners must be welded or brazed to ensure continuity. The flashing must have a minimum height of 150 mm above the finished roof surface.

Rake and Ridge Flashing

Rake Flashing (Roof Edge)

Rake flashing protects the free edge of the roof. It must:

Extend at least 50 mm beyond the roof edge.

Include a drip edge.

Be covered by the roof membrane for at least 100 mm.

Be fastened to the structure (not just to the roof deck).

Ridge Flashing

Ridge flashing (for sloped roofs) is typically an angle or arched profile that covers the ridge line. It must:

Cover both slopes by at least 150 mm each.

Be vented if the roof is ventilated (vented ridge).

Have longitudinal overlaps of at least 100 mm in the direction opposite to prevailing winds.

Expansion Joints and Thermal Movement

Calculating Thermal Expansion

The coefficient of thermal expansion α varies by material:

Material	α (×10⁻⁶ /°C)	Expansion for 6 m and ΔT = 50 °C
Galvanized steel	12	3.6 mm
Aluminum	23	6.9 mm
Copper	17	5.1 mm
Stainless steel	16	4.8 mm

Calculation formula: ΔL = α × L × ΔT

Where ΔL is the change in length, L is the initial length, and ΔT is the temperature change.

Example: A 6 m long aluminum coping subjected to a temperature change of 50 °C will expand by: 23 × 10⁻⁶ × 6000 × 50 = 6.9 mm.

Expansion Joints

Expansion joints in copings and flashing must:

Be provided at regular intervals (6 m for steel, 3 m for aluminum).

Allow movement without tearing the sheet metal.

Be covered with a cap-shaped cover plate that allows sliding.

Be sealed with an expansion joint sealant (polyurethane or silicone).

Applicable Standards and Codes

National Building Code of Canada (NBC)

The National Building Code of Canada 2020 contains requirements for flashing and copings, including:

Article 9.26.4.1: General requirements for flashing — flashing must be installed at junctions between the roof and vertical elements.

Article 9.26.4.2: Flashing materials — flashing must be corrosion-resistant metal, plastic, or other impermeable material.

Article 9.26.4.3: Flashing installation — flashing must be installed so as to direct water to the exterior.

Article 9.26.5.1: Copings — parapets and walls must be protected by a coping.

CSA Standards

CSA A123.5: Flashing and accessories for roofing — material specifications and test methods.

CSA G164: Galvanized steel sheet.

CSA S304: Design of masonry structures (for flashing embedment).

Canadian Standards Council Guidelines

The Flashing Selection Guide published by the Canadian Standards Council (in collaboration with the Canadian Roofing Contractors Association) recommends standard details for each roof configuration. These details are widely used as a reference in the industry and on exams.

Detailed Installation Procedures

Installing Base Flashing on a Parapet

128.Preliminary check: Ensure the roof membrane is carried up at least 150 mm onto the parapet.

129.Forming the flashing: Form the piece with a horizontal leg of 100 mm and a vertical leg of 150 mm minimum.

130.Sealant application: Apply a bead of butyl or polyurethane sealant on the vertical face of the parapet.

131.Flashing installation: Apply the flashing against the parapet, with the horizontal leg resting on the roof.

132.Fastening: Fasten the vertical leg with large-head nails or screws spaced at 300 mm maximum.

133.Covering: Cover the horizontal leg with the roof membrane over its full width.

134.Counter-flashing installation: Embed the counter-flashing into the mortar joint or reglet, ensuring it overlaps the base flashing by at least 100 mm.

Installing a Parapet Coping

136.Support preparation: The top of the parapet must be clean, dry, and level.

137.Underlayment installation: Install a bituminous underlayment or self-adhering membrane on top of the parapet.

138.Coping forming: Form the piece with a 1:50 slope, 25 mm vertical returns, and drip edges.

139.Installation: Install the coping starting at the low point, orienting overlaps in the direction opposite to prevailing winds.

140.Fastening: Fasten through the high portion (if using through-fasteners) or using side clips.

141.Sealing: Seal all joints and overlaps with a compatible sealant.

Quality Control and Inspection

Mandatory Checkpoints

Checkpoint	Acceptance Criteria
Base flashing/counter-flashing overlap	≥ 100 mm
Flashing height above roof	≥ 150 mm
Coping slope	≥ 1:50
Fastener spacing	≤ 300 mm
Masonry embedment	≥ 25 mm
Expansion joints	Every 6 m (steel), 3 m (aluminum)
Drip edge	Present on all free edges

Common Defects to Identify

Flashing too short: insufficient height above the roof.

Insufficient overlaps: less than 100 mm.

Missing drip edge: water migrates back up by capillary action.

Unsealed through-fasteners: points of water entry.

Reverse slope: water pools instead of draining.

Incompatible sealant: premature degradation, insufficient adhesion.

Safety Considerations

Working at Height

Flashing and coping installation is often performed at roof edges or on parapets. Safety requirements include:

Use of an anchorage system compliant with CSA Z259.16 (fall protection systems).

Wearing a safety harness connected to a lifeline.

Use of scaffolding or aerial work platforms for work at height.

Verification of support strength before anchoring the system.

Sheet Metal Handling

Sheet metal has sharp edges. Wearing cut-resistant gloves and safety glasses is mandatory. Sheets must be stored flat, protected from wind, and handled with care.

Pitfalls to Avoid

162.Confusing minimum overlaps: The longitudinal overlap between flashing pieces is 100 mm, but the overlap of the base flashing by the counter-flashing is also 100 mm. Do not confuse this with the roof membrane overlap over the flashing (150 mm).

163.Forgetting the drip edge: A coping without a drip edge allows water to migrate back up by capillary action under the sheet metal, causing leaks.

164.Neglecting thermal expansion: A 6 m aluminum coping without an expansion joint will deform and pull out its fasteners.

165.Using incompatible fasteners: Steel screws in copper cause rapid galvanic corrosion.

166.Installing base flashing over the roof membrane: Base flashing must be covered by the membrane, not the other way around.

167.Forgetting the slope on horizontal surfaces: Any horizontal flashing or coping surface must have a minimum slope of 1:50.

168.Not sealing through-fasteners: Every through-fastener is a potential entry point for water.

169.Confusing sheet metal thicknesses: The minimum thickness for commercial flashing is 0.61 mm (24 gauge), not 0.46 mm (28 gauge).

170.Ignoring expansion joints: They are mandatory at regular intervals, not just at changes in direction.

171.Installing counter-flashing before base flashing: The installation order is critical: base flashing first, then counter-flashing over it.

Summary

Flashing, copings, and sheet metal details are the most critical components of a roofing system when it comes to watertightness. The essential points to remember for the Red Seal exam:

Minimum overlaps: 100 mm for flashing, 75 mm for copings, 150 mm for roof membrane over flashing.

Minimum slopes: 1:50 (2%) for all horizontal sheet metal surfaces.

Minimum heights: 150 mm above the finished roof surface for base flashing.

Fasteners: Spaced at 300 mm maximum, sealed if through-fasteners.

Materials: Galvanized steel (0.46 mm residential, 0.61 mm commercial), aluminum, copper, stainless steel — each with its specific requirements.

Thermal expansion: Expansion joints every 6 m (steel) or 3 m (aluminum), calculated with ΔL = α × L × ΔT.

Standards: NBC 2020 articles 9.26.4 and 9.26.5, CSA A123.5, CSA G164.

Installation order: Base flashing, then roof membrane, then counter-flashing, then coping.

Drip edge: Mandatory on all free edges to break capillary action.

Mastery of these principles and their correct application on the job site distinguishes the qualified roofer. On the exam, questions frequently focus on minimum overlaps, slopes, sheet metal thicknesses, and installation order. Memorize the key values and the underlying physical principles, and you will be well prepared for this section.

Flashing, Copings, and Sheet Metal Details