Architectural Sheet Metal and Roofing

Introduction to the Field

Architectural sheet metal and roofing represent a major competency area for the journeyperson sheet metal worker. This field encompasses the fabrication, installation, and maintenance of all sheet metal elements that protect the building against weather while ensuring an aesthetic and functional finish. For the Red Seal exam, you must master design principles, installation techniques, development calculations, and applicable Canadian regulatory requirements.

This chapter covers the essential skills: roof types, minimum slopes, flashings, roof gutters, eaves troughs, soffits, ridges, hips, valleys, penetrations, as well as surface area and development calculations. Particular attention is given to the rules of the trade and common pitfalls that cause candidates to fail.

Materials Used in Architectural Sheet Metal

Steel Sheets

Steel is the most common material for architectural applications. Distinctions include:

Galvanized steel: coated with zinc by hot-dip immersion (G90, G60). Used for roof gutters, eaves troughs, flashings, and soffits. Nominal thickness ranges from 0.38 mm (26 gauge) to 1.52 mm (16 gauge).

Pre-painted steel (or organic-coated steel): galvanized steel covered with a layer of paint or polymer (PVDF, polyester). Offers increased durability and a range of colors.

Stainless steel: alloyed with chromium (minimum 10.5%) and often nickel. Resists corrosion, used for monumental roofs, high-quality flashings, and corrosive environments. Common types: 304 and 316 (316 contains molybdenum for better chloride resistance).

Non-Ferrous Metals

Copper: excellent corrosion behavior, develops a green patina (verdigris) over time. Common thicknesses: 0.46 mm (16 oz) to 0.81 mm (24 oz). Requires specific welding and brazing techniques.

Aluminum: lightweight, corrosion-resistant, available in smooth or corrugated sheets. Thicknesses from 0.61 mm to 1.27 mm. Watch out for high thermal expansion (approximately 2× that of steel).

Zinc (zinc-titanium): zinc alloyed with titanium and copper. Service life of 60 to 100 years. Requires isolation from contact with steel, copper, and treated wood (galvanic corrosion).

Thermal Expansion — Essential Data

Material	Coefficient of Linear Expansion (×10⁻⁶ /°C)	Expansion for 10 m for ΔT = 60 °C
Steel	12	7.2 mm
Aluminum	24	14.4 mm
Copper	17	10.2 mm
Zinc	22	13.2 mm
Stainless steel	16	9.6 mm

Rule of thumb: for a 15 m long steel roof with a ΔT of 70 °C, the total expansion is 15 × 12 × 10⁻⁶ × 70 = 0.0126 m = 12.6 mm. Expansion joints must absorb this variation.

Roof Types and Slopes

Slope Classification

A roof slope is expressed as a vertical/horizontal ratio (e.g., 1:4) or as a percentage. The National Building Code of Canada (NBC) and CSA standards impose minimum slopes depending on the type of roofing.

Roofing Type	Minimum Slope	Remarks
Asphalt shingles	1:6 (≈ 9.5°)	Below this, use a membrane
Corrugated metal	1:12 (≈ 4.8°)	With standing seam: 1:24 possible
Standing seam	1:24 (≈ 2.4°)	Requires watertight seams
Copper or zinc (standing seam)	1:12	Recommended minimum slope
Elastomeric membrane	1:50 (≈ 1.1°)	Flat roof
Corrugated sheet	1:6	Minimum overlap of 150 mm

Standing Seam Roofs

The standing seam is a sheet metal roofing system where adjacent panels are joined by folded vertical seams. Distinctions include:

Single standing seam: one fold on each panel, stapled or crimped.

Double standing seam: two folds, more watertight, recommended for low slopes.

Clip seam (or batten seam): panels are fastened with concealed clips, allowing free expansion.

Panels are fastened to the substrate with fixed clips (at one end) and sliding clips (along the panel) to allow for expansion. Typical panel width is 300 mm to 600 mm.

Corrugated Metal Roofs

Corrugated sheets (profiled) are used for industrial, commercial, and agricultural roofs. Common profiles include:

7.2 cm profile (2.8 in): high rib, span up to 1.5 m.

3.8 cm profile (1.5 in): medium rib.

Trapezoidal profile: high rigidity, span up to 3 m.

Fasteners are exposed (self-drilling screws with sealing washers) or concealed (for certain profiles). Fastener spacing is 300 mm on supports and 150 mm at edges.

Flashings and Roof Accessories

Definition and Role

A flashing is a sheet metal element that ensures watertightness at the junction between two surfaces (roof and wall, roof and chimney, etc.). Flashings must be installed with a minimum overlap of 100 mm and a slope directed outward to drain water.

Types of Flashings

Flashing Type	Location	Key Requirements
Edge flashing	Roof edge	Return of at least 25 mm over the edge
Ridge flashing	Roof peak	Minimum 150 mm overlap
Valley flashing	Junction of two slopes	Minimum width of 300 mm on each side
Penetration flashing	Chimney, vent	Top flange of 100 mm, side flange of 75 mm
Wall flashing	Wall/roof junction	Extend up the wall a minimum of 150 mm
Counter-flashing	Above wall flashing	Recessed into masonry joint by 25 mm

Valley Flashing — Installation Technique

The valley is the re-entrant angle formed by the meeting of two roof slopes. The valley flashing must be installed before the roofing is laid. The rules of the trade require:

41.Total minimum width of 600 mm (300 mm on each side of the centerline).

42.Center crease (break) of at least 25 mm to direct water.

43.Overlap of valley sections: 150 mm minimum, in the direction of water flow.

44.Fastened with clips or screws spaced 300 mm maximum, only at the edges (never in the center).

45.Roofing sheets must cover the valley by at least 150 mm on each side.

Roof Gutters and Eaves Troughs

Difference Between Roof Gutter and Eaves Trough

A roof gutter (chéneau) is a channel built into the roof or located at the roof/wall junction, generally large in size, that collects rainwater. An eaves trough (gouttière) is a channel suspended from the edge of the eave, of more modest cross-section.

Drainage Area Calculation

The drainage area (or catchment area) is the horizontal projection of the roof surface that feeds a roof gutter or eaves trough. For a gable roof, each eaves trough collects half of the projected area.

Basic formula:

Drainage area (m²) = Projected slope length (m) × Trough length (m)

Example: a 12 m × 8 m roof (horizontal projection) with eaves troughs on both long sides. Each trough drains 12 m × 4 m = 48 m².

Sizing Eaves Troughs

Sizing depends on the local rainfall intensity (given by climatic tables) and the slope of the trough. A slope of 1:200 to 1:100 is recommended (5 mm to 10 mm per metre).

Drained Area (m²)	Minimum Trough Width (mm)	Downspout Diameter (mm)
Up to 30	100	75
30 to 60	125	100
60 to 100	150	125
100 to 150	175	150
Over 150	200	2 downspouts of 125

Important rule: each section of eaves trough between two downspouts must not exceed 12 m. Beyond that, add an additional downspout.

Slope and Installation of Eaves Troughs

The slope must be continuous and directed toward the downspout.

Joints between trough sections must be watertight (solder, rivet + sealant, or snap-fit connector with gasket).

Supports (hangers) are spaced 600 mm maximum for aluminum and 750 mm for galvanized steel.

The back edge of the trough must be raised at least 25 mm under the roof edge.

The downspout must be fastened to the wall with brackets spaced 1.8 m maximum.

Soffits and Eaves

Definition

The soffit is the horizontal or inclined surface that closes the underside of the eave. It provides roof ventilation and protects the structure.

Attic Ventilation

Ventilation is essential to prevent condensation and ice formation. The NBC rule requires a total net ventilation area of at least 1/300 of the attic floor area, distributed 50% at the air intake (soffits) and 50% at the air outlet (ridge).

Calculation example: for a 120 m² attic, the required total net ventilation is 120 / 300 = 0.4 m². You therefore need 0.2 m² of soffit ventilation and 0.2 m² of ridge ventilation.

Types of Soffits

Type	Material	Characteristics
Solid soffit	Perforated or non-perforated sheet	Ventilation through perforations
Vented soffit	Sheet with perforations	Net ventilation area indicated by manufacturer
Continuous soffit	Roll of sheet metal	Quick installation, fewer joints

The net ventilation area of a perforated soffit is generally 40% to 60% of the gross area. Check the manufacturer's data.

Development and Surface Area Calculations

Sheet Development

Development is the flat surface area needed to fabricate a three-dimensional piece. For bent pieces, add the lengths of the straight segments and the developed lengths of the bends.

Formula for a 90° bend:

Developed length = R + t

where R is the inside bend radius and t is the sheet thickness. For an acute or obtuse bend, use the formula:

Developed length = (π × R × θ) / 180

where θ is the bend angle in degrees.

Example: an L-shaped piece with two segments of 100 mm and 50 mm, bent at 90° with an inside radius of 3 mm and a thickness of 1 mm.

Developed length = 100 + 50 + (3 + 1) = 154 mm

Surface Area of a Sloped Roof

The actual surface area of a sloped roof is greater than its horizontal projection. The correction factor is the inverse of the cosine of the slope angle.

Formula:

Actual surface area = Projected area / cos(slope angle)

Example: a 10 m × 8 m roof with a 30° slope.

Projected area = 80 m². Actual area = 80 / cos(30°) = 80 / 0.866 = 92.4 m².

Number of Sheets Required

To cover a surface, divide the actual area by the usable area of each sheet (total area minus overlaps). Always round up to the next whole number and add 5% to 10% for waste and cuts.

Example: 92.4 m² roof with 0.9 m × 3 m sheets (usable area of 2.7 m² after overlap).

Number of sheets = 92.4 / 2.7 = 34.2 → 35 sheets. With 10% waste: 35 × 1.1 = 38.5 → 39 sheets.

Applicable Codes and Standards

National Building Code of Canada (NBC)

The NBC, published by the National Research Council of Canada (NRC), establishes minimum requirements for design and construction. Relevant sections for architectural sheet metal include:

Section 5.10: Protection against water infiltration — requirements for flashings, roof gutters, and eaves troughs.

Section 9.26: Roof covering — minimum slopes, overlaps, fastening.

Section 9.29: Exterior cladding — soffits, wall flashings.

CSA Standards

Canadian Standards Association (CSA Group) standards are frequently cited in specifications:

CSA A123: series of standards on roofing materials (asphalt shingles, membranes).

CSA G401: galvanized steel sheets for general applications.

CSA S16: design of steel structures (relevant for roof supports).

Canadian Electrical Code, Part I

Although this code concerns electricity, it is relevant to architectural sheet metal with respect to grounding and bonding of metal roofs. Rule 8-200 requires that exposed exterior metal surfaces likely to be touched be grounded. A metal sheet roof must be grounded in accordance with this rule, with a bonding conductor of appropriate size (minimum 6 AWG copper or 4 AWG aluminum).

Other Relevant Standards

CSA B149.1: Natural gas and propane installation code — relevant for roof penetrations (chimney vents, exhaust ducts).

CAN/CSA A660: certification of sheet metal roof installers.

Installation Procedures — Typical Sequence

Step 1: Substrate Preparation

Verify the flatness and slope of the substrate.

Install a vapour barrier and membrane if required.

Install lath or a continuous substrate according to the type of roofing.

Step 2: Installation of Base Flashings

Install valley, edge, and penetration flashings before the roofing.

Verify overlaps and drainage slopes.

Step 3: Installation of Roofing

Install panels from bottom to top (in the direction of water flow).

Respect side and end laps.

Fasten according to prescribed spacing.

Step 4: Installation of Finish Flashings

Install ridge flashings, counter-flashings, and wall flashings.

Seal joints with a compatible sealant.

Step 5: Installation of Roof Gutters and Eaves Troughs

Install supports before the finish roofing.

Install troughs with the required slope.

Connect downspouts.

Step 6: Final Inspection

Verify watertightness of joints.

Ensure all fasteners are in place.

Clean up debris and metal shavings.

Pitfalls to Avoid

133.Confusing projected area and actual area: always use the actual area to calculate material quantities. The projected area is only used for drainage calculations.

134.Neglecting thermal expansion: rigid fasteners (screws in standing seams) prevent free expansion and cause sheet buckling. Use sliding clips.

135.Insufficient slope on eaves troughs: a slope of less than 1:200 causes water stagnation and debris accumulation. Check with a level.

136.Forgetting soffit ventilation: insufficient ventilation area leads to condensation and mould. Calculate the net area, not the gross area.

137.Insufficient flashing overlap: an overlap of less than 100 mm allows capillary infiltration. Always respect the minimums.

138.Using incompatible materials: direct contact between aluminum and copper causes galvanic corrosion. Isolate with a gasket or sealant.

139.Fastening valleys in the center: screws in the center of the valley pierce the water flow zone and create infiltration points. Fasten only at the edges.

140.Forgetting grounding: a metal roof not grounded poses a danger during lightning strikes. Comply with Rule 8-200 of the Canadian Electrical Code.

141.Confusing gauge and thickness: gauge is not a linear measurement. 26 gauge corresponds to 0.38 mm for steel but 0.45 mm for aluminum. Always check the tables.

142.Not accounting for snow loads: trough supports and fasteners must resist snow and ice loads. Check local values.

Summary

Architectural sheet metal and roofing require precise mastery of materials, techniques, and standards. The essential points to remember for the Red Seal exam:

Materials: know the characteristics of galvanized steel, aluminum, copper, and zinc, as well as their expansion coefficients.

Slopes: respect minimum slopes according to roofing type (1:24 for standing seam, 1:6 for shingles).

Flashings: minimum 100 mm overlap, slope directed outward, edge fastening for valleys.

Eaves troughs: slope of 1:200 to 1:100, support spacing of 600 to 750 mm, maximum 12 m section between downspouts.

Ventilation: net area of 1/300 of the attic area, distributed 50% at the soffit and 50% at the ridge.

Calculations: actual area = projected area / cos(angle), bend development with the formula R + t for a 90° bend.

Standards: NBC sections 5.10, 9.26, and 9.29; CSA A123, G401; Canadian Electrical Code Rule 8-200 for grounding.

Expansion: always provide expansion joints and sliding fasteners for long lengths.

Success on the exam depends on your ability to apply these principles to practical situations. Practice with surface area, drainage, and development calculations, and memorize the key values from the tables in this chapter.

Architectural Sheet Metal and Roofing