Notes to TPO Standard

Division B - Standards

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Notes to Standard for TPO Membrane 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

Notes to Part 2

A-2.7 (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 as used in 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 this 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

Notes to Part 4

Notes to Part 5

Notes to Part 6

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 (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 (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-7.1.3.4 (Tapered Insulation and Crickets)

The effective thermal resistance of any insulation is dependent on location and other intervening factors (penetrating screw fasteners, for example) which may diminish the performance of the insulation panel. Effective thermal resistance of sloped or tapered insulation is not the same as the average value, using the minimum and maximum thermal resistance of a panel. For help with these calculations, use the RoofStar Effective Thermal Resistance Calculator for Sloped Insulation.

Notes to Part 8

A-8.1 (Design)

Insulation overlay boards are installed in most conventionally insulated systems to

• protect heat-sensitive insulation materials from damage by heat and flame.
• protect insulation materials from accidental impact.
• provide dimensional stability to the roof system.
• distribute dead loads from heavy overburdens or equipment installed on top of the finished waterproofing system.
• ensure the membrane performs as it should.
• provide a suitable substrate for membrane application.

Insulation overlay boards may be mechanically attached or adhered, depending upon the insulation type and the design requirements of the entire roof assembly.

Notes to Part 9

A-9.1.2.2 (All Projects - Membrane Protection)

Sunlight reflected from windows, doors, cladding and other reflective materials can elevate roof surface and sub-surface temperatures, which may shorten the life of a membrane and the roof system materials beneath it, and may cause irreparable damage. Roofs oriented to face south and southwest are particularly vulnerable to these effects, and sunlight reflected from metal can be more damaging than light reflected by glass.

For more about this phenomenon, read The Impact of Solar Reflectivity of Glazing Adjacent Roofs, published in the Summer 2021 issue of RoofingBC.

Notes to Part 10

A-10.1.2.2 (All Projects - Membrane Protection)

Restoration is required to prevent fire, and to ensure the EIFS is not vulnerable to insect infestation or contamination. Also refer to EIFS Council of Canada Practice Manual.

Refer to The British Columbia Building Code, Division B, Part 3, Section 3.1, Subsection 3.1.4. Combustible Construction: Article 3.1.4.1., Combustible Materials Permitted, and to Article 3.1.4.2., Protection of Foam Plastics.

Notes to Part 11

Notes to Part 12

Notes to Part 13

Notes to Part 14

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