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<div id=A-7.1.3.4.></div>

<div id=A-7.1.3.4.></div>

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====A-7.1.3.4. Effective Thermal Resistance and Layering====

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====A-7.1.3.4. {{strike| Effective || 2026-January-28 }} {{hilite | Thermal Resistance and Layering|| 2027-February-1 }}====

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

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

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

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

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<div id=A-7.1.3.4.(4)></div>

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===={{hilite | A-7.1.3.4.(4) Thermal Bridging and Dewpoint|| 2026-February-1 }}====

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:{{hilite | While every effort is made by suppliers and installers to keep roofing materials dry, some moisture will always find its way inside the built assembly, usually turning to vapour.  In certain climates and weather conditions, particularly because of snow cover, the dew point may fall inside the ''roof assembly'', turning entrapped water vapour to liquid on a condensing surface, such as a metal girt.  Water inside the ''roof system'' can reduce thermal performance, cause corrosion (e.g., on the cut edges of girts, which are not galvanized), and may present as a leak inside the building due to discontinuities in assembly intersections (roof-to-wall) or vapour and air control layers.  Condensation of any sort is not a leak and therefore isn't covered by a '''''RoofStar Guarantee''''' (Refer to || 2026-February-1 }} [https://rpm.rcabc.org/index.php?title=Guarantee#3.2.1.2._Limitations_and_Exclusions_of_Guarantee {{hilite | Article 3.2.1.2.|| 2026-February-1 }}]{{hilite | in Division A of the RPM for limitations and exclusions).  Consequently, the ''Design Authority'' must consider the overall thermal performance expectations of the roof, along with the design requirements for (or, in the case of roof replacement, the condition of) the entire building enclosure, and use appropriate methods for supporting panel clips|| 2026-February-1 }}.

<div id=A-7.1.4.2.></div>

<div id=A-7.1.4.2.></div>

Notes to ASM Standard - Revision history

James Klassen at 18:38, 30 January 2026

James Klassen: /* A-2.1.5.5. All Wood Roof Decks */