CSA A123.16-04 (2006): Application of Asphalt Shingles on Steep Roofs — Technical Overview

Scope and Purpose

CSA A123.16-04 (2006) — Asphalt Shingles on Steep Roofs — Application — establishes minimum requirements for the installation of asphalt shingles on roofs with a slope of 2:12 (approximately 9.5 degrees) or greater. This standard is referenced in the Canadian National Building Code and serves as the primary guideline for residential and light-commercial steep-slope roofing systems. It covers all essential aspects of shingle application including underlayment, exposure, fastening, flashing details, and valley construction. The 2006 reaffirmation ensures continued alignment with industry practices and climatic considerations specific to Canada.

Technical Requirements for Asphalt Shingle Application

Slope and Deck Preparation

The standard mandates that asphalt shingles be applied only on roofs with a slope of 2:12 or greater. For slopes between 2:12 and 4:12, special low-slope application methods (e.g., increased underlayment layers, sealed courses) are required. The roof deck must be solid, dry, and smooth; typical acceptable materials include plywood, OSB, and spaced lumber (for slopes ≥ 4:12). Any irregularities exceeding 5 mm over a 600 mm span must be corrected before shingle application.

Underlayment Requirements

Underlayment must comply with CSA A123.3 (asphalt-saturated felt) or CSA A123.17 (synthetic underlayment). For roofs with slopes between 2:12 and 4:12, the standard requires a double layer of underlayment lapped 48 inches (1220 mm) horizontally and 6 inches (152 mm) vertically. For slopes ≥ 4:12, a single layer lapped 2 inches horizontally and 6 inches vertically is acceptable. Underlayment must extend at least 12 inches (305 mm) up vertical walls and into valleys.

Shingle Exposure and Fastening

Standard exposure for 3-tab shingles is 5 inches (127 mm) for slopes ≥ 4:12 and 4 inches (102 mm) for slopes 2:12 to 4:12. Laminated shingle exposure is as per manufacturer specifications. Fasteners must be corrosion-resistant (hot-dip galvanized, stainless steel, or aluminum) with a minimum head diameter of 9.5 mm and a shank diameter of 2.67 mm. Each shingle tab requires at least four fasteners placed in a straight line above the cutout, 5/8 inches (16 mm) from each end and equally spaced. The table below summarizes the fastener requirements:

Flashing and Valleys

Valleys must be constructed using either woven, closed, or open methods, each with specific material and overlap requirements. The standard mandates at least 1.5 mm thick prefinished metal valley flashing extending 300 mm on each side of the valley centerline. Step flashing at sidewalls must be at least 150 mm high and 100 mm wide, integrated with the shingle course. For roof-to-wall intersections, counterflashing must be embedded at least 25 mm into the wall masonry or sealant. All flashings must be corrosion-resistant.

Ventilation and Ridge Details

Ridge and hip shingles must be cut from standard shingles, with a minimum exposure of 130 mm. The standard requires a minimum of two fasteners per ridge shingle. Adequate attic ventilation (1:300 ratio) is mandated to prevent moisture accumulation and premature shingle aging.

Implementation Highlights for Contractors

Adherence to CSA A123.16-04 involves several on-site practices that directly affect durability and warranty compliance:

• Deck moisture testing: The deck must be dry at time of installation (moisture content below 16% for wood).
• Chalk lines: Guidelines are mandatory to ensure straight horizontal and vertical alignment, especially for steep slopes where visual drift is pronounced.
• Low-slope procedures: For slopes 2:12–4:12, a full-width sealed strip (e.g., self-adhering membrane) is required along the eave edge to prevent ice dam back-ups.
• Weather limitations: The standard prohibits installation when temperatures fall below 4°C (40°F) unless warm-stored shingles or manufacturer-approved cold weather adhesives are used.

Manufacturers often include additional requirements beyond the standard; their specifications must be followed to maintain the shingle warranty. The standard itself notes that where the manufacturer’s instructions are more stringent, those instructions take precedence.

Compliance and Verification Notes

Enforcement of CSA A123.16-04 typically falls under provincial building codes and municipal inspection. Key points for verification:

• Documentation: The contractor should provide a statement of compliance with the standard and include fastener schedule, underlayment type, and slope verification.
• Inspection checkpoints: Deck condition, underlayment laps, fastener count and penetration, flashing integration, and ridge vent clearance.
• Conflict resolution: In case of conflict with the National Building Code or local by-laws, the stricter requirement governs. The standard explicitly states it does not override seismic or wind uplift requirements from referenced documents like CSA O86 or NBCC 2005.

The standard also references test methods from ASTM D3462 (asphalt shingles) and ASTM D3161 (wind resistance). Wind classification (H, G, or F) must match the design wind speed for the building location as per NBCC.

Note: CSA A123.16-04 (2006) is a reaffirmation of the original 2004 edition. Users should check if the project requires compliance with a later edition, such as CSA A123.16-12 or A123.16-17, which may contain updated climate zone maps and ice dam protection requirements.

© 2026 — Content prepared for informational purposes. Always refer to the official standard for full requirements.