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:Cutting the existing membrane is also necessary to relieve diaphragm-like tension that could distort the new ''roof system'', particularly at the perimeter.  It also allows any existing moisture in the roof system to move around and prevents the existing membrane from acting as an intermediate vapour retarder that could adversely affect the performance of the recovered ''roof system''.

:Cutting the existing membrane is also necessary to relieve diaphragm-like tension that could distort the new ''roof system'', particularly at the perimeter.  It also allows any existing moisture in the roof system to move around and prevents the existing membrane from acting as an intermediate vapour retarder that could adversely affect the performance of the recovered ''roof system''.

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<div id=A-1.1.4.4.(9).></div>

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===={{hilite | A-1.1.4.4.(9) Recovering Membranes in a Protected Assembly || 2026-October-31  }}====

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:{{hilite | When an in-service membrane is demonstrably secure (fully bonded to the roof ''deck'' – adhesion of the membrane for wind uplift resistance must be tested, and the test results submitted to the '''''Guarantor''''' with the request for a Variance), it is blister-free, and it is free of damage, the '''''Guarantor''''' may permit the application of a new membrane directly to the existing membrane, without requiring membrane removal or the application of an intermediate overlay board. || 2026-October-31 }}

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====A-2.1.5.5. Overlays for Mass Timber Decks====

====A-2.1.5.5. Overlays for Mass Timber Decks====

:An overlay may be required by the ''manufacturer'' for these types of wood decks to protect membranes from wood sap, deck surface irregularities, and protruding fasteners.

:An overlay may be required by the ''manufacturer'' for these types of wood decks to protect membranes from wood sap, deck surface irregularities, and protruding fasteners.

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<div id=A-2.1.5.6.></div>

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===={{hilite | A-2.1.5.6. Non-veneered Panel Roof Decks || 2026-October-31 }}====

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:{{hilite | In 2024, the "Special Interest Group for the Dynamic Evaluation of Roof Systems" (SIGDERS) completed a study of wood ''decks'' and the holding strength of mechanical fasteners used in membrane ''roof systems''. They found significantly low resistance values from all grades of non-veneered wood ''decks'' (e.g., oriented strand board, or OSB) when compared with 12.7 mm (1/2") fir plywood. As a result, the study recommended avoiding non-veneered wood panels for commercial roof decking|| 2026-October-31 }}.

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:{{hilite | Following the findings of the SIGDERS study, the requirements for decking found in the RGC Standards for waterproofing roofs have been amended to prohibit fastening to a non-veneered wood deck unless it is overlaid with suitable plywood.  For a summary of the study, read the article by Dr. A. Baskaran's "Application of Wood As Decking Component", published in || 2026-October-31 }} [https://www.mediaedgemagazines.com/roofing-contractors-association-of-britishcolumbia-rcabc/rc251/ {{hilite | Volume 22, Number 1 of Roofing BC|| 2026-October-31 }}].

<div id=A-2.1.7.></div>

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:{{hilite | 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. || 2023-June-16 }}

:{{hilite | 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. || 2023-June-16 }}

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<div id=A-7.1.5.2.></div>

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===={{hilite | A-7.1.5.2. Waterproofing Roof Systems on Uninsulated, Vented Wood-Frame Structures || 2026-October-31 }}====

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:{{hilite | Some roofs on older wood-framed buildings (often Multi-Unit Residential Buildings, or MURBs) are still protected by built-up ''roof systems'' (BURs) that have aged past their end-of-service date. Topped with small-sized gravel, these roofs absorb and reflect heat energy that keeps the roof ''deck'' warm and dry, even through cool nights. Buildings of this design are usually insulated between the joists below the roof deck and often, though not always, there is a 'ventilation' cavity between the insulated joists and the underside of the ''deck''. These older buildings are also characteristically air-leaky, carrying water vapour into the roof cavity. However, because of the properties of the old BUR ''roof system'', condensation on the underside of the deck has never been an issue || 2026-October-31 }}.

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:{{hilite | Where condensation and subsequent deterioration of the roof deck has occurred, even when the ventilation meets Section 9.19 of the Building Code, it appears to be associated with replacement roof designs that did not account for the thermal properties of the former BUR roof assembly. Condensation can be a problem in marine climate regions (such as along the British Columbia coast) where higher relative humidity values, especially when combined with the night sky effect, cause condensation on the underside of the roof ''deck'' (See the two studies on asphalt shingle roofs commissioned by BC Housing, with support from the RCABC - [https://www.bchousing.org/publications/Asphalt-Shingle-Sloped-Roofing-Research-Study.pdf Phase 1] and [https://www.bchousing.org/publications/Field-Evaluation-Roof-Treatments-Report.pdf Phase 2]). Therefore, when designing a roof for a new wood-framed building or a replacement ''roof system'' for an existing BUR roof, the ''Design Authority'' should consider the potential for condensation on the underside of the roof ''deck'' and design the new ''roof system'' to prevent it. This may be accomplished by evaluating the effectiveness of ventilation below the deck ensuring it is not obstructed), or by insulating the new roof system above the deck and using darker membranes, but any mitigation strategies such as the addition of above-deck insulation must be carefully considered and calculated by the ''Design Authority'' || 2026-October-31 }}.

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:{{hilite | When the existing roof system cannot be easily removed from the supporting deck (for example, a BUR system that was mopped directly to wood), the ''Design Authority'' should consider the 'recover' option in || 2026-October-31 }} [[SBS Roof Systems Standard#Part 1 - General |{{hilite | Part 1 || 2026-October-31 }}]] {{hilite | of this Standard || 2026-October-31 }}.

<div id=A-7.2.2.3.></div>

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====A-11.1.4.2. Scuppers and Overflows====

====A-11.1.4.2. Scuppers and Overflows====

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:{{hilite | 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. || 2023-June-16 }}

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:{{hilite | 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. || 2023-June-16 }}

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:{{hilite | Where ''overflows'' are not located at the roof edge and are instead located in the roof field, they should be plumbed separately from ''primary roof drains''. Currently, the National Plumbing Code of Canada (and the British Columbia Plumbing Code which is modelled after it) do not stipulate how ''overflows'' must be plumbed. However, that is expected to change with the 2025 NPC and subsequently with the British Columbia Plumbing Code.  “Emergency roof drainage systems” will have to be independent of (separately plumbed from) the “primary roof drainage system”. Furthermore, “A storm building drain serving both the primary and emergency roof drainage systems, as described in Clause 2.6.6.6.(3)(a), shall be sized for 200% of the calculated hydraulic load determined in accordance with Subsection 2.4.10.” (Proposed Change 1790, Canadian Board for Harmonized Construction Codes, February 2024). The illustration below, adapted from PC1790, captures the concept. However, ''overflows'' situated at the roof perimeter are recommended, where the design permits it; ''overflows'' that share drain leaders, regardless of leader capacity, should be avoided || 2026-October-31 }}.

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::{|

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|-

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|-

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| colspan="1"; style="text-align:center;width:450px;" | {{hilite | '''Figure A-11.1.4.2.-1 Illustration adapted from PC1790, NPC''' || 2026-October-31 }}<br>{{hilite | Forming Part of Note A-11.1.4.2. || 2026-October-31 }}<br><small>(Click to expand illustration)</small>

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|-

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| [[File:Part 11 Notes - Figure 1 of A-11.1.4.2.-A.png|link=https://rpm.rcabc.org/images/7/79/Part_11_Notes_-_Figure_1_of_A-11.1.4.2.-A.png |600 px]]

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|}

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:{{hilite | The location of the ''drainage plane'' depends on the type of ''roof system''. On a ''conventionally insulated roof'' with an exposed membrane (no ''overburden''), the ''drainage plane'' and the field membrane are synonymous. However, ''overburden'' displaces water upward, shifting the location of the ''drainage plane'' with it. The location of ''overflows'' must take this into account || 2026-October-31 }}.

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:{{hilite | The ''drainage plane'' of a ''protected membrane roof assembly'' is also affected by displacement (XPS insulation and ballast), and also by how water-permeable the filtration layer is. Low-permeable materials tend to direct most water to the drains across the filtration layer plane, so that very little water finds its way down to the roof membrane. Highly permeable filtration materials, when they are new, admit considerable water into the ''roof system''; water works its way down to the roof membrane, between and around XPS panels. However, as protected membrane roofs age, water-permeable filtration layers will tend to cake with fine debris so that they function more like impermeable fabrics || 2026-October-31 }}.

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:{{hilite | When ''overflows'' are located at the same plane as ''overburden'' or stone roof ballast, they must be protected with ballast guards from blockage by water-displaced materials || 2026-October-31 }}.

<div id=A-11.1.4.3.></div>

<div id=A-11.1.4.3.></div>

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Grade 316L stainless steel has high amounts of chromium and nickel, much like grade 304 stainless, and it also contains silicon, manganese, and carbon (in addition to iron). However, grade 316 stainless steel also contains 2 to 3 percent molybdenum (by weight), compared to only trace amounts found in 304 stainless steel. Higher molybdenum content produces a superior corrosion-resistant stainless steel. Grade 316L stainless steel is often considered one of the most suitable choices for marine applications.

Grade 316L stainless steel has high amounts of chromium and nickel, much like grade 304 stainless, and it also contains silicon, manganese, and carbon (in addition to iron). However, grade 316 stainless steel also contains 2 to 3 percent molybdenum (by weight), compared to only trace amounts found in 304 stainless steel. Higher molybdenum content produces a superior corrosion-resistant stainless steel. Grade 316L stainless steel is often considered one of the most suitable choices for marine applications.

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<div id=A-13.2.2.1.(4)></div>

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===={{hilite | A-13.2.2.1.(4) Coefficient of expansion and securement of linear metal flashings|| 2026-October-31 }}====

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{{hilite | The coefficient of thermal expansion is the mathematical expression of linear movement one can expect of a particular metal when it is exposed to changes in temperature. Alloys will change these properties, which is why it is important to know the metal's composition. || 2026-October-31 }}

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{{hilite | Because the degree of linear movement increases with flashing length, the ''registered professional'' responsible for designing ''linear metal flashing'' securement should consider anchoring the mid-point of very long flashings to allow for bi-directional expansion. However, each solution presents its own challenges. Affixing flashings at an end or in the middle forces expansion and contraction away from the anchoring point. This must be considered when designing a system of flashings where each length of material is attached to another. || 2026-October-31 }}

===<big><span class="reference">Notes to Part 14</span></big>===

===<big><span class="reference">Notes to Part 14</span></big>===

Notes to PVC Standard - Revision history

James Klassen at 14:43, 31 October 2025

James Klassen at 21:12, 26 June 2025