Notes to ASM Standard

Division B - Standards

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Notes to Standard for Architectural Sheet Metal (ASM) Roof Systems

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(Notes are explanatory and non-binding, each provided to support the requirements, guiding principles and recommendations of the Standard.)

Notes to Part 1

A-1.1.3.1. (Permitted Roof Systems)

Metal roofing panels are roll-formed in full rafter length pans that are fastened to decks with metal clips and screws, or are manufactured with perforations or slots to facilitate concealed fastening. Galvanized steel and wood are the most common deck materials used with architectural metal roofing.

A-1.1.3.2. (Snow Loads)

To determine if a building is located in a high snow load area, the Design Authority must calculate the anticipated snow loads for the roof, using the building code having jurisdiction. The following references are extracted from the British Columbia Building Code:

• Div. B, 4.1.6.2 Specified Snow Load (see the formula for calculating snow loads).
• Div. B, Appendix C, Table C-2 which lists various types of loads, including snow loads, for specific reference locations throughout the province.

A-1.1.3.5. (Hot Works)

When any portion of a waterproofing system is installed with heat, the work is classified as Hot Works. Some tools used in the course of Hot Works can ignite combustible materials, and some building environments are more sensitive to fire than others, such as a building containing or in close proximity to flammable liquids. Hot works may occur during

• tear off (sparks).
• deck preparation (drying wet surfaces).
• cold temperatures (warming materials or surfaces).
• equipment use (sparks within electrical tools, or from cutting, drilling, or grinding metal, concrete, stone, or other hard surface products).
• membrane installation (with the means of a kettle, hot-air welder, or open flame torch).

A-1.1.4. (Alterations and Additions)

As a roof ages, is neglected or is damaged, it may lose its ability to perform reliably and effectively, necessitating replacement. Replacement roofing, also referred to as "re-roofing," whether made in whole or in part, should be undertaken with the Quality Assurance and Quality Control provided for under the RoofStar Guarantee Program. Regardless of the approach to replacement roofing, the existing deck structure must meet the pullout resistance rating for mechanical fasteners and must be capable of supporting all dead and live loads. Furthermore, the deck must be capable of supporting any additional dead loads of the new roof system.

A-1.3.3.2. (Workmanship)

While integrity and functionality of a new roof or grade-level waterproofing is the foundation of a RoofStar Guarantee, it is no less important to ensure that the finished project exhibits excellent workmanship.

Notes to Part 2

A-2 (Scope and Application of Part 2)

Part 2 addresses deck and wall materials, deck slope, deck and wall conditions, and the methods by which intersecting systems such as electrical wiring can be executed safely and in alignment with the interests of the Guarantor. It does not address construction or installation of decks and walls, which is the work of other trades. For the preparation of a roof deck to render a deck or wall suitable for roofing, refer to Part 9 and Part 10, in the articles pertaining the substrate preparation.

A-2.1.5.1. (Steel Roof Decks)

Steel decks are constructed of light gauge (usually 22, 20, or 18 gauge) cold-rolled steel sections (panels) that are usually galvanized. In cross-section the panels are ribbed, with the ribs usually spaced at 150 mm (6") O.C. The ribs provide the strength and rigidity of the panels. Steel decks are generally supported by open-web steel joist framing and are welded or mechanically fastened to the framework.

A-2.1.5.2. (Concrete Roof Decks)

Concrete decks generally are not suitable as a substrate for Architectural Sheet Metal Roofing, and must be overlaid with a material to which the roof system can be mechanically affixed.

A-2.1.5.3. (All Wood Roof Decks)

Wood is a common roof deck construction material that has been used for many years because of its economy, ease of fabrication, lighter construction, and ready availability. Acceptable wood roof decks may include (without limitation)

• wood board (tongue-and-groove, ship-lapped, or splined boards or planks that typically range in thickness from 19 mm to 89 mm (nominal 1" to 4"). Wood board decks may also include Mill Decks which are also called Nail-Laminated Timber decks. These are constructed with a single layer of dimensional boards (dimensions can vary), placed on edge and spiked together to form a Mill Deck. The thickness of the boards is determined by the anticipated loads and spacing of roof joists or trusses.
• plywood (exterior type plywood mechanically fastened to the roof framing).
• non-veneered (oriented strand board, waferboard, etc.).
• laminated timber (typically comprised of crossing layers of dimensional solid wood material, laminated to form a thick, dimensionally stable slab strong enough to support significant structural loads).

A-2.1.5.4.(1) (All Wood Roof Decks)

There are eight (8) exterior grades of plywood used in Canada, and the Canadian Wood Council (CWC) identifies and explains each of them in their published article, "Plywood grades" (https://cwc.ca/wp-content/uploads/2019/03/Plywood-Grades.pdf). Because grades vary, it is incumbent upon the Design Authority to specify the correct grade for roof decking.

A-2.1.7. (Walls)

Walls and roofs intersect either directly (where the wall structurally connects to the roof structure, so that both move together), or indirectly (where the roof structure and the wall structure are independent of each other, so that the movement of one does not affect the other). These locations require an expansion joint.

A-2.1.8. (Electrical Cables and Boxes)

Electrical boxes, fixtures, and electrical wiring (exposed or protected inside conduit) installed inside, on top of, or beneath a roof assembly may present hazards for roofing workers and building occupants and may interfere with the roof design.

Many Tested Assemblies (roof assemblies tested under controlled conditions) rely on mechanical fasteners to secure some or all materials. Roof fasteners (which are self-drilling so they can penetrate steel decking) are capable of penetrating even the most rigid electrical conduit. When roofing screws contact an energized electrical system, workers can be shocked, sometimes with lethal consequences. Furthermore, electrical conductors damaged by roofing screws may not trip fault protection devices which generally do not respond to high-resistance faults. High-resistance electrical faults have been linked to numerous structural fires, which sometimes occur years after conductors were damaged. For these reasons, separating the electrical service from the roof assembly is critical.

Electrical conductor damage is not a problem exclusive to new construction. As roofs wear out and require partial or full replacement, mechanical fastening is often the only way by which new roof materials can be secured to the structural roof deck, to comply with the Building Code. When electrical systems are hidden by existing roof system materials, the design and construction of a replacement roof may be exceedingly difficult to execute.

Rule 12-022 of the "2021 Canadian Electrical Code, Part I", now prohibits the installation of “cables or raceways” within a roof assembly. Rule 12-022 is reprinted below (the term “roof decking system” used in the Rule has the same meaning as roof assembly used by ASTM International (ASTM D6630-08, "Standard Guide for Low slope Insulated Roof membrane Assembly Performance"), and by this Standard):

12-022 Cables or raceways installed in roof decking systems

1) Cables or raceways installed in accordance with this Section shall not be installed in locations concealed within a roof decking system, where the roof systems utilises screws or other metal penetrating fasteners.

2) Notwithstanding Subrule 1) the following circuits shall be permitted for installations in locations concealed within a roof decking system:

a) Class 2 circuits in which the open-circuit voltage does not exceed 30 V; and

b) embedded trace heat.

3) Where wiring is concealed within the roof deck system in accordance with Subrule 2), a warning label shall be installed

a) at all permanently installed roof access points where provided; and

b) in a conspicuous location in the roof area where the cabling is installed.

While Rule 12-022 permits the installation of cables and raceways within a roof system that does not utilize "screws or other metal penetrating fasteners", doing so is inadvisable; unlike electrical systems that are more or less permanent, roof systems must be renewed, usually multiple times over the course of a building's expected service life. Often, when the roof system is only partially renewed (for reasons of economy, or to limit the amount of material entering the waste stream), mechanical fasteners offer the best option for securing new materials to those left in situ. Obviously, electrical systems located anywhere close to the roof assembly pose high risks to both the Contractor during construction and may introduce a fire risk to building occupants later (for more on this subject, see the Information Centre in Division E). Providing considerable separation between electrical systems and the roof assembly, and ensuring that electrical services to rooftop equipment utilize purpose-made penetrations that can be sealed into the roof system, will serve the Owners well for the service life of the building.

Rule 12-022 is a national code requirement directly resulting from a years-long endeavor by the RCABC, provincial adoption of the Canadian Electrical Code, Part I may be delayed because of the British Columbia code cycle. Nevertheless, the Design Authority is advised to adopt the requirements and prohibitions of the national Code, and to also adopt the following requirements for new construction or replacement roofing, as they apply.

Notes to Part 3

A-3.1.1.1. (Scope)

Wind exerts tremendous forces on a roof system, regardless of roof type. While wind is commonly experienced as a “pushing” force, wind also generates “negative” (pulling or “uplift”) forces, particularly on flat roofs. These powerful forces can, if the roof system is poorly secured to the building’s structural elements, detach a portion or all of a roof system from the building.

The Code refers to these calculated forces as Specified Wind Loads, which act in concert with the “responses of the roof system…[and therefore] are time-and-space dependent, and thus are dynamic in nature.” (CSA Standard A123.21, "Standard test method for the dynamic wind uplift resistance of membrane-roofing systems" (latest edition), 4.1). Because of this dynamic interplay between loads and a building’s structural capacities (the load paths between the roof system and other structural elements of the building), the Design Authority must design a roof capable of effectively absorbing and mitigating Specified Wind Loads.

As stated earlier, the calculation of Specified Wind Loads falls under "British Columbia Building Code", Division B, Subsection 4.1.7., "Wind Loads", while the securement of the roof components system to resist Specified Wind Loads is governed by the "British Columbia Building Code", Division B, Article 5.2.2.2., "Determination of Wind Load".

A-3.1.1.2. (Intent)

In December 2018 the Province of British Columbia released a revised edition of the "British Columbia Building Code" (the "Code"), based on the 2015 "National Building Code of Canada". The 2018 Building Code includes a considerable expansion of the requirements in Division B, Part 4 (see "British Columbia Building Code", Division B, Subsection 4.1.7., "Wind Loads") applicable to the loads exerted on a roof system by wind. The careful reader will note that these Part 4 requirements apply to all Part 3 buildings and to some Part 9 structures.

While the expansion of Part 4 addresses the calculation of dynamic wind loads experienced by a roof assembly, Part 5 ("Environmental Separation") specifies how a roof system should be secured to resist Specified Wind Loads (see the "British Columbia Building Code", Division B, Article 5.2.2.2., "Determination of Wind Load").

Article 5.2.2.2. of the Building Code applies almost exclusively to conventionally insulated roof systems and is specifically oriented to sheet membrane roof systems. While sheet membrane conventionally insulated roof systems are prolific and perhaps the most common type of waterproofing roof system, the Building Code offers little guidance for other roof types, including uninsulated roof systems, liquid membrane systems, systems insulated above the membrane (referred to as “inverted” or “protected”), and steeply sloped roofs (greater than 1:6, or 2" in 12"). This Standard incorporates design and construction guidance, even where the Code appears to offer little or no support.

Proper securement of the roof system, to resist wind uplift loads, is good practice. It also fulfills the design and construction objectives of the Code, to guard public safety, and it supports the design objectives of the RoofStar Guarantee Program, to keep weather outside of the building. In this Part, the reader will find explanatory notes and aids in the design and construction of a roof intended to be Code-compliant.

A-3.1.3.4. (Design to Resist Other Loads)

By design, most architectural standing seam metal panel systems are intended to float to provide freedom for thermal expansion and contraction. Proprietary attachment clip designs permit metal panels to slide back and forth on the clip as the panel expands and contracts during the thermal cycle. Live snow loads can create considerable drag on panels displacing them from their intended location. The most common place to install drag load fasteners (point of fixity) is at the roof ridge, which allows fasteners to be concealed by cap flashing.

Notes to Part 4

Notes to Part 5

A-5 (Deck and Wall Overlays)

This Part addresses materials that are acceptable as overlays used to render a deck or wall surface suitable for roofing. This Part supports the substrate preparation requirements in Parts 9 and 10.

A-5.1.3.1. (Required Use of Overlays)

A roof deck overlay (also called a system underlay) is installed as part of the roof system, on the top surface of the roof deck but beneath other roofing materials. These products are most commonly affixed to steel decks to provide a level surface for the roof membrane, to support air or vapour control layers, or to serve as a thermal barrier between the roof deck and combustible insulation. Roof deck overlay materials may also be applied to other types of supporting deck structures, depending on the roof design criteria.

Notes to Part 6

A-6 (Air and Vapour Controls)

Part 6 is a boilerplate wording included in every Standard of the RoofStar Guarantee Program, regardless of whether or how air and vapour controls are used in a roof assembly.

Air and vapour controls, whether manufactured as sheet products or as liquids, form a critical component of the suite of building enclosure systems used to regulate the movement of air and water vapour in and out of the building. Because continuity is critical not only within an assembly but also between assemblies, performance of air and vapour control materials is not covered by the RoofStar Guarantee; the RoofStar Guarantee Program is limited to the scope of a roof system, and therefore it has no control over the construction or performance of adjoining assemblies, such as walls, which may adversely impact the performance of the roof system. Nevertheless, the choice of materials used in a roof system is still critical for its performance. Therefore, this Part prohibits certain materials because, from a constructability standpoint, they are difficult to seal (to achieve continuity) and are often fragile and prone to puncture during construction. Furthermore, this Part includes both design and construction requirements intended to achieve continuity, since the transfer of air and the movement of water vapour into the roof system can produce false leaks that undermine the objectives of the Standard.

A-6.1.1.1. (Scope)

Air and vapour control layers, along with thermal barriers, water resistive barriers and water-shedding surfaces, serve to separate the outside environment from the interior environments of a structure. Continuous air control layers are perhaps the most critical. Codes in each jurisdiction, and the "2020 National Energy Code of Canada for Buildings" (NECB), require the selection and proper installation of “a continuous air barrier system comprised of air-barrier assemblies"..."to control air leakage into and out of the conditioned space” ("National Energy Code of Canada for Buildings", Part 3, Article 3.2.4.1., "General").

Air control layers regulate and often prohibit the “flow of air through the building enclosure, either inward or outward” (Guide for Designing Energy Efficient Building Enclosures, Homeowner Protection Office). Controlling air flow into and out of conditioned spaces affects the performance of “thermally efficient enclosure assemblies” (ibid), impacts the potential for condensation in between materials, and directly influences rain water penetration of the building envelope.

Vapour control layers regulate or prohibit the movement of water vapour from one space to another by means of diffusion. Consequently, these control layers are referred to as either vapour-permeable or impermeable. Diffusion is a slow process, in contrast to air movement, and its regulation is not always mandatory or even desirable.

Any references in this Manual to installation methodologies, and any construction details that show air and vapour control layers, are merely illustrative and not prescriptive. Installers of continuous air and vapour control layer systems are urged to understand and comply with best practices for their application.

A-6.1.3.1. (Responsibility for Design)

Air and vapour control layer performance is not part of the RoofStar Guarantee, and air and vapour control materials are not listed in Division C.

In some roof assembly designs, the required underlayment may serve as an air control layer, vapour control layer, or both; this is dependent upon the properties of the material to be used and will be subject to the designer’s modelling of the assembly. Consult the Technical Data Sheets for suitable materials.

A-6.2.1.2. (Prohibited Materials for RoofStar Guarantee)

Constructability, and resistance to damage, heat, and to solvent-based products, are key properties of air and vapour control materials. While the RoofStar Guarantee does not extend coverage to air and vapour control materials, or to their performance (Ref. Note A-6, "Air and Vapour Controls"), leaks through or past damaged or poorly sealed materials can adversely affect the performance of the guaranteed roof system. For this reason, both polyethylene plastic sheet products and bitumen-impregnated kraft paper are not permitted in a roof intended to qualify for a RoofStar Guarantee; both materials are easily damaged (punctured) during construction, and proper sealing of each material to itself and to adjoining materials is difficult.

Notes to Part 7

A-7.1.3.1 (Responsibility for Design)

Insulation materials rely on various standards for the determination of thermal resistance, which means that not all data can be easily compared. Furthermore, not all insulation products perform with consistent thermal resistance as temperature changes, and some insulation performance declines with age. Therefore, refer to the "Long-term Thermal Resistance" (LTTR) for each insulation product, in relation to the product's placement within the roof assembly and the anticipated outside and interior climates of the building.

Also see the "British Columbia Building Code", Division B, Part 10 (Ref. Div. B, Section 9.25., "Heat Transfer, Air Leakage and Condensation Control" for structures governed by Part 9), together with relevant requirements in Division A and Division C of the Building Code.

A-7.1.3.2. (General Requirements)

Wood is the typical deck material used for Architectural Sheet Metal Roof Systems, and when the slope is less than 1:3 (4" in 12"), a self-adhered underlayment is required. However, because wood is organic, and because wood both accumulates and retains moisture during and after construction, it is critical that the roof deck be ventilated on at least one face, to permit drying. Some polymeric underlayments are manufactured to allow the diffusion of moisture escaping from a wood deck, but when a self-adhered membrane is applied to a low-sloped roof deck, nothing will vent upward through the underlayment. Ventilation below the deck is therefore critical, or the deck may decay.

A-7.1.3.4. (Effective Thermal Resistance and Layering)

In warm seasons, the roof surface may reach temperatures higher than 85°C (185°F), affecting the performance and stability of some insulation. Consequently, the requirement which limits panel size in single-layer applications ensures that inevitable gaps between adjacent panels are kept to a minimum. Combining insulation types in a roof system may help mitigate these temperature swings and the consequence of thermal contraction. The Design Authority therefore must consider these variables when specifying materials and their installation.

The "Long-Term Thermal Resistance" (LTTR) measurement of closed-cell insulation materials remains the standard by which insulation performance is measured. Published R-values should reflect the LTTR of the material. In Canada, two principal standards apply to the accurate measurement of thermal resistance: CAN/ULC-S770 ("Standard Test Method for Determination of Long-Term Thermal Resistance of Closed-Cell Thermal Insulating Foams") and CAN/ULC-S704.1 ("Standard for Thermal Insulation, Polyurethane and Polyisocyanurate, Boards, Faced").

A-7.1.4.2. (Protection of Heat-sensitive Insulation)

Heat-sensitive insulation can be distorted and even damaged when absorbed solar radiation raises the temperature of the insulation above its published maximum service temperature rating (usually 70 - 75°C). Severe damage can reduce the thermal resistance of the insulation system; damaged panels have been known to contract, causing depressions and increasing gaps between adjacent panels.

The requirement to use a layer of heat-resistant insulation on top of heat-sensitive insulation is based on a mathematical modeling of the buffering effects of different overlay strategies. While modeling showed some insulation overlay panels reduced some absorbed heat, none reduced heat below the service temperature of the insulation, and none provided sufficient margin to allow for high-heat weather events. Only heat-resistant insulation measuring at least 50 mm (2") thick offered the necessary level of protection to prevent insulation damage.

A-7.2.2.3. (Polyisocyanurate Insulation)

Since September 1, 2010, the RGC has excluded organic-faced polyisocyanurate insulation from the RoofStar Guarantee Program, because of moisture-induced cupping and curling attributed to the composition of the facer material. Only fibre-glass or acrylic facers are accepted by the Guarantor for use on roofs qualifying for a RoofStar Guarantee.

Notes to Part 8

A-8.1.3.5. (Ventilation Beneath Panels)

Condensation on the bottom face of metal panels is a normal occurrence. To permit drying, a "ventilation" cavity immediately beneath the panels is required. The purpose of the cavity is not ventilation as defined by the Building Code in Part 9. Rather, it is strictly an air space between materials to ensure water does not remain trapped against the panel, which could promote corrosion or (in the case of an insulated roof system) reduce thermal performance. Ventilation of an unconditioned space beneath the roof assembly must be achieved by other means, which are the responsibility of the Design Authority and fall outside the scope of this Standard.

Notes to Part 9

A-9.1.3.1. (System Design)

By design, most architectural standing seam metal panel systems are intended to float to provide freedom for thermal expansion and contraction. Proprietary attachment clip designs permit metal panels to slide back and forth on the clip as the panel expands and contracts during the thermal cycle. Live snow loads can create considerable drag on panels displacing them from their intended location. The most common place to install drag load fasteners (point of fixity) is at the roof ridge, which allows fasteners to be concealed by cap flashing.

A-9.2.1.5. (Clips)

Refer to Note A-3.1.3.4.

Notes to Part 10

A-10.1.6.1. (Expansion Joints)

Roof expansion joints, or movement joints, are designed to safely absorb thermal expansion and contraction of materials, or to absorb vibration. They also allow for movement caused by settlement and earthquakes.

Notes to Part 11

A-11.1.4.2. (Scuppers and Overflows)

The primary function of an overflow is to keep a roof from collapsing when primary roof drains are plugged or cannot drain heavy rainfall. New and existing buildings should incorporate overflows to handle large rain events. Refer to the "British Columbia Building Code" and the "British Columbia Plumbing Code" for drain sizing and location requirements.

A-11.1.4.3. (Membrane Gutters)

Gutters designed with downward-draining flanged drains need sufficient width to properly secure and seal the flange to the gutter membrane system. Gutters narrower than 300 mm compromise this critical detail, either by forcing the installer to trim the flange to fit the gutter width (which can compromise securement of the drain body), or by reducing the breadth of membrane needed to properly seal the drain flange to the gutter bottom. Gutters designed with cast-iron drains must be at least 100 mm (4") wider than the width of the drain body, to permit a sufficient membrane seal; more width is better, improving the effectiveness of the drain installation.

A-11.2.1.2. (Roof Drains and Scuppers)

Roof drains are comprised mainly of two parts: a bowl or flange that is affixed to the roof deck with mechanical fasteners or a proprietary clamping mechanism; and an integral drain stem that connects the bowl or flange to the leader. Roof drains are sized according to the diameter of the drain stem. The appropriate size and number of roof drains for any given roof area is determined by the relevant building code in force (ref. British Columbia Plumbing Code, Division B, Part 2; Article 2.4.10.4 Hydraulic Loads from Roofs or Paved Surfaces).

Roof drains can be further classified as internal or external. Internal roof drains are connected to leaders located and connected to a storm building drain or sewer inside the exterior surface of a building. Internal roof drains may be made of cast iron (secured to the roof assembly with clamps) or from copper or aluminum, fashioned from spun components that are welded together and incorporate a flange around the drain bowl.

External roof drains direct storm water outside the exterior surface of a building. Scuppers and overflow drains are the common types of external roof drains, and may connect to leaders or simply drain freely. Any requirements for leaders and connections to leaders may be found in the applicable municipal and provincial building and plumbing codes (ref. British Columbia Building Code, Division B, 5.6.2.2 Accumulation and Disposal).

Notes to Part 12

Notes to Part 13

Notes to Part 14

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