Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
CSA A123.5-16: Standard Practice for the Application of Asphalt Shingles on Roofs
Guidelines for proper installation, materials, and quality control in asphalt shingle roofing
CSA A123.5-16 – Standard Practice for the Application of Asphalt Shingles on Roofs – is a comprehensive Canadian standard developed by the Canadian Standards Association (CSA Group) to govern the proper field installation of asphalt shingles. It provides complete requirements for substrate preparation, underlayment materials, fastening systems, flashing details, and final shingle placement. The standard is periodically updated to reflect improvements in material science and field experience; the 2016 edition includes clarifications on ice-dam protection, low-slope applications, and fastener corrosion resistance.
Adherence to CSA A123.5-16 is essential for roofing contractors, building inspectors, architects, and homeowners to ensure durable, weather-tight roof assemblies. This article examines the key elements of the standard, with a focus on scope, technical requirements, installation best practices, and compliance pathways.
1. Scope and Application
CSA A123.5-16 applies to the field application of asphalt shingles on roof slopes ≥ 1:6 (approximately 2:12 or greater) for new construction and re-roofing. It covers both organic‑felt and glass‑fibre asphalt shingles, including strip shingles, individual shingles, and interlocking shingles. The standard also addresses low‑slope roofs (1:6 to 1:2) where special ice‑dam and underlayment provisions are required.
Key elements within the scope include:
- Minimum roof slope for asphalt shingle application
- Substrate requirements (deck type, condition, slope tolerances)
- Underlayment selection and overlap
- Fastener type, size, quantity, and corrosion resistance
- Shingle exposure, alignment, and offset patterns
- Flashing at hips, ridges, valleys, vents, and vertical walls
- Application in cold weather conditions
The standard does not cover built‑up roofing, modified‑bitumen membranes, or synthetic roofing products. It is intended to be used in conjunction with the shingle manufacturer’s written instructions; where a conflict arises, the manufacturer’s requirements take precedence provided they do not violate the minimum performance levels of CSA A123.5-16.
Tip: Always verify that the specific shingle product is listed as complying with the applicable material standard (CSA A123.1 or CSA A123.2) before referencing CSA A123.5-16 for installation.
2. Technical Requirements
2.1 Roof Slope and Deck Preparation
The standard requires the roof deck to be smooth, dry, and free from debris. The minimum allowable slope for standard asphalt shingles is 1:6 (about 2:12). For slopes between 1:6 and 1:2 (2:12 to 6:12), a minimum of two layers of underlayment or a self‑adhering membrane is required on all deck areas to prevent moisture ingress at low slopes.
2.2 Underlayment
CSA A123.5-16 specifies underlayment materials conforming to CSA A123.3 (asphalt‑saturated felt) or alternative approved products. The standard’s minimum requirements are summarised in Table 1 below.
| Roof Slope | Underlayment Type | Minimum Number of Layers | Lap Spacing (horizontal) | Lap Spacing (vertical / ridge) |
|---|---|---|---|---|
| ≥ 6:12 (≥26.6°) | No. 15 felt or equivalent | 1 | ≥ 75 mm | ≥ 150 mm |
| < 6:12 but ≥ 2:12 | No. 30 felt or self‑adhering membrane | 2 (felt) or 1 (membrane) | ≥ 150 mm | ≥ 225 mm |
| Any slope with ice‑dam risk | Ice‑dam membrane (self‑adhering) | 1 (as required along eaves) | ≥ 75 mm | ≥ 150 mm |
Table 1 – Underlayment requirements per CSA A123.5-16 based on roof slope and climate considerations.
Important: The standard requires a self‑adhering ice‑dam membrane (compatible with the shingle) to extend at least 900 mm (approx. 36 inches) from the roof edge in regions where ice dams are common. This distance may be increased if required by the building code or manufacturer.
2.3 Fasteners
Fasteners must be hot‑dipped zinc‑coated (galvanised) or stainless steel. The standard requires:
- Minimum shank diameter: 3.0 mm (for roofing nails) or 2.7 mm (for staples)
- Minimum length: 19 mm (3/4 inch) for applications into plywood or OSB decks; 25 mm (1 inch) for thicker boards or where deck thickness is unknown
- Minimum nail head diameter: 9.5 mm (3/8 inch)
- Fastener quantity: 4 nails per strip shingle (or 5 in high‑wind areas > 140 km/h) with corrosion‑resistant coating consistent with local exposure
2.4 Shingle Exposure and Layout
CSA A123.5-16 defines the maximum allowable shingle exposure based on slope and shingle type. For a typical three‑tab strip shingle on a roof ≥ 4:12, the exposure is the distance marked on the shingle (commonly 5 inches or 127 mm). On lower slopes, the exposure must be reduced to ensure a triple‑coverage pattern. The shingles should be offset between courses by a minimum of one tab (approx. 150 mm), and no cutouts should be aligned within two courses.
Best practice: Use the shingle manufacturer’s recommended nailing pattern (nails at 12.7 mm (½ inch) above cutouts) and place nails in the course just above the cutout to avoid bulge and premature cracking.
3. Implementation Highlights
3.1 Valleys and Flashing
Valley flashing must be of at least 0.41 mm (26‑gauge) galvanised steel or a proper roll‑valley membrane system. The standard requires open valleys to have a minimum 150 mm wide centre opening, while closed “woven” valleys are allowed only on slopes ≥ 6:12. Every intersection with a wall, chimney, or skylight requires a base flashing (step or continuous) and a counter‑flashing.
3.2 Ridge and Hip Installation
Ridge and hip shingles are cut from full shingles or pre‑fabricated. Exposure at the ridge should be approximately one‑half the normal exposure to provide a finished appearance and adequate coverage. The ridge must be ventilated unless an unvented assembly is designed.
3.3 Cold Weather Application
When ambient temperatures are below 4 °C, the standard warns that asphalt shingles become brittle and seals may not activate. Recommendations include:
- Warming shingles before installation
- Using hand‑sealing with asphalt cement to pre‑seal tabs
- Avoiding heavy foot traffic on the freshly laid roof
Caution: Do not install asphalt shingles during rain, snow, or when the deck is wet. Moisture trapped under the shingles can lead to blistering, curling, and premature failure.
4. Compliance and Certification Notes
CSA A123.5-16 is a voluntary consensus standard, but it is referenced by the National Building Code of Canada (NBC) and most provincial building codes as an accepted method of installing asphalt shingles. Therefore, compliance is effectively mandatory for installers seeking code acceptance.
4.1 Certified Products
Shingles, underlayment, and ice‑dam membranes bearing the CSA mark (or equivalent third‑party listing) verify that the product meets the material requirements of the relevant CSA A123 series standard. The installer must follow the marking and handling directions affixed to each bundle.
4.2 Field Verification
During inspection, the building authority will check:
- Slope and deck condition
- Underlayment type, number of layers, and lap distances
- Fastener type, length, spacing, and quantity
- Exposure length and offset
- Flashing details at all roof penetrations and terminations
Any deviation from CSA A123.5-16 must be justified by an engineer or documented as a product‑specific exemption.
4.3 Re‑Roofing
For re‑roofing over existing shingles, the standard allows an additional layer provided the old roof does not exceed one layer, the deck is sound, and the total added weight is within the structural capacity. Fasteners must be long enough to penetrate at least 19 mm into the deck or sheathing.
Important for re‑roofing: Many jurisdictions now prohibit adding a third layer; check local building code. Always remove old layers if the deck is damaged or if multiple layers are present.
Frequently Asked Questions
Q: What is the minimum roof slope for asphalt shingles according to CSA A123.5-16?
A: The minimum slope is 1:6 (approximately 2:12). For slopes between 1:6 and 1:2, additional underlayment is required, and the manufacturer’s instructions may further restrict application on such low slopes. Standard shingles should not be used on slopes below 2:12; a low‑slope membrane or torch‑on system should be considered instead.
A: The minimum slope is 1:6 (approximately 2:12). For slopes between 1:6 and 1:2, additional underlayment is required, and the manufacturer’s instructions may further restrict application on such low slopes. Standard shingles should not be used on slopes below 2:12; a low‑slope membrane or torch‑on system should be considered instead.
Q: Are staples an acceptable fastener under CSA A123.5-16?
A: Yes, staples are permitted provided they have at least a 2.7 mm crown width, a minimum shank diameter of 2.7 mm, and are driven vertically with the crown parallel to the shingle’s long dimension. However, for high‑wind areas or when required by the manufacturer, roofing nails (with larger head and higher pull‑out resistance) are often preferred.
A: Yes, staples are permitted provided they have at least a 2.7 mm crown width, a minimum shank diameter of 2.7 mm, and are driven vertically with the crown parallel to the shingle’s long dimension. However, for high‑wind areas or when required by the manufacturer, roofing nails (with larger head and higher pull‑out resistance) are often preferred.
Q: Does CSA A123.5-16 address ice‑and‑water membrane?
A: Yes. The standard requires a self‑adhering membrane along the eave edge in areas where ice damming is expected (typically extending 900 mm above the interior wall line). The membrane must be compatible with both the underlayment and the asphalt shingles. Many shingle manufacturers also include their own membrane as part of their warranty package, and the standard allows that as long as it meets the same performance criteria.
A: Yes. The standard requires a self‑adhering membrane along the eave edge in areas where ice damming is expected (typically extending 900 mm above the interior wall line). The membrane must be compatible with both the underlayment and the asphalt shingles. Many shingle manufacturers also include their own membrane as part of their warranty package, and the standard allows that as long as it meets the same performance criteria.
Q: How often is CSA A123.5 updated?
A: The standard is reviewed every five years on a regular cycle. The 2016 edition replaced the 2011 version, and a more recent revision (A123.5:21) has been published. However, many jurisdictions still reference the 2016 edition in transitional periods. Always confirm the version accepted by your local building authority.
A: The standard is reviewed every five years on a regular cycle. The 2016 edition replaced the 2011 version, and a more recent revision (A123.5:21) has been published. However, many jurisdictions still reference the 2016 edition in transitional periods. Always confirm the version accepted by your local building authority.
For the most accurate and detailed text, readers should obtain the official CSA A123.5-16 document from the CSA Group or its authorised distributor. This article presents a professional summary based on publicly available information and industry experience.
— Published 2026 —