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Part 5 governs the building envelope of Part 3 buildings: how walls, roofs and floors control heat, air, vapour and rain. It is written in performance language, so exam questions focus on three things: what each Section requires the assembly to achieve, the shared "not required where it can be shown" escape clause, and which standard applies to windows, air barriers and EIFS. The Building Services syllabus takes Sections 5.3, 5.4, 5.5, one precipitation Article (5.6.1.1.) and Section 5.9.
Heat transfer
Any component or assembly subject to an intended temperature differential must include materials that resist heat transfer, or a means to dissipate the heat OBC Div. B 5.3.1.1.OBC Div. B 5.3.1.1. Required Resistance to Heat Transfer(1) Except as provided in Sentence (2), where a building component or assembly will be subjected to an intended temperature differential, the component or assembly shall include materials to resist heat transfer or a means to dissipate transferred heat in accordance with the remainder of this Subsection. (2) The…. The amount of resistance is not a fixed RSI in Part 5 (Part 12 and SB-10 set energy values). Instead, it must be enough to OBC Div. B 5.3.1.2.OBC Div. B 5.3.1.2. Properties to Resist Heat Transfer or Dissipate Heat(1) Taking into account the conditions on either side of the environmental separator, materials and components installed to provide the required resistance to heat transfer or the means implemented to dissipate heat shall provide sufficient resistance or dissipation, (a) to minimize surface condensation on the warm…:
- minimize surface condensation on the warm side,
- minimize condensation within the assembly (working with the other layers),
- meet the interior design temperature with the heating and cooling systems, and
- minimize ice damming on sloped roofs.
Where insulation is interrupted by an intersecting assembly, a high conductance element or a joint, and condensation is likely there, extra thermal resistance is needed at that spot. Insulation must also resist airflow, or be positioned to prevent convective looping through and around it OBC Div. B 5.3.1.3.OBC Div. B 5.3.1.3. Location and Installation of Materials Providing Thermal Resistance(1) Where a material required by Article 5.3.1.1. is intersected by a building assembly, penetrated by a high conductance component or interrupted by expansion, control or construction joints, and where condensation is likely to occur at these intersections, penetrations or interruptions, sufficient thermal resistance….
Air leakage and vapour diffusion
Air leakage. An assembly separating conditioned space from outdoors, from the ground, or from an environmentally dissimilar interior space must control air leakage (or vent to the exterior) for six stated reasons, including occupant comfort, condensation and rain control, ice damming, soil gas such as radon, and not compromising building services OBC Div. B 5.4.1.1.OBC Div. B 5.4.1.1. Required Resistance to Air Leakage (Note A-5.4.1.1.)(1) Where a building component or assembly separates interior conditioned space from exterior space, interior space from the ground, or environmentally dissimilar interior spaces, the properties and position of the materials and components in those components or assemblies shall be such that they control air leakage…. The air barrier system is the assembly that forms a continuous barrier to air movement definitionOBC Div. A 1.4.1.2.(1) Air barrier systemAir barrier system means the assembly installed to provide a continuous barrier to the movement of air.. It must be continuous across construction, control and expansion joints, across junctions between assemblies, and around penetrations. Assemblies meet a Performance Class from the code's air leakage table.
Air barrier standards OBC Div. B 5.4.1.2.OBC Div. B 5.4.1.2. Air Barrier Assemblies(1) Except as provided in Sentences (2) and (3), air barrier assemblies not in contact with the ground shall (a) conform with CAN/ULC-S742, "Standard for Air Barrier Assemblies – Specification," and (b) meet the selected Performance Class of Table 5.4.1.1. (See Note A-5.4.1.2.(1)) (2) Air barrier assemblies not…:
| Case | Standard named |
|---|---|
| Above-grade air barrier assembly | CAN/ULC-S742 (assembly specification) |
| Assembly not evaluated to S742 | Must meet the Performance Class and include at least one material meeting CAN/ULC-S741 |
| Windows, other fenestration, EIFS | The criteria in Subsections 5.9.2. to 5.9.4. |
| Below grade, in contact with ground | Minimize ingress of radon and other soil gases |
Vapour diffusion. Where an assembly sees differences in temperature and vapour pressure, a vapour barrier (the elements installed to control diffusion of water vapour) provides the principal resistance OBC Div. B 5.5.1.1.OBC Div. B 5.5.1.1. Required Resistance to Vapour Diffusion(1) Where a building component or assembly is subjected to differentials in temperature and water vapour pressure, the properties and position of the materials and components in those components or assemblies shall be such that they control vapour diffusion or permit venting to the exterior so as to minimize…. Its permeance and position must keep diffusion from reaching surfaces cold enough to condense, or slow it so moisture never builds up enough to cause damage OBC Div. B 5.5.1.2.OBC Div. B 5.5.1.2. Vapour Barrier Properties and Installation(1) The vapour barrier shall have sufficiently low permeance and shall be positioned in the building component or assembly so as to (a) minimize moisture transfer by diffusion, to surfaces within the assembly that would be cold enough to cause condensation at the design temperature and humidity conditions, or (b)…. Coatings on gypsum board are tested to CAN/CGSB-1.501-M; coatings on other materials to ASTM E96 by the dry cup (desiccant) method.
Precipitation OBC Div. B 5.6.1.1.OBC Div. B 5.6.1.1. Required Protection from Precipitation(1) Except as provided in Sentence (2), where a building component or assembly is exposed to precipitation, the component or assembly shall (a) minimize ingress of precipitation into the component or assembly, and (b) prevent ingress of precipitation into interior space. (2) Protection from ingress of precipitation is…: an exposed assembly must minimize ingress of rain into the assembly and prevent it reaching interior space.
The common escape clause. Each of 5.3.1.1., 5.4.1.1., 5.5.1.1. and 5.6.1.1. has the same exception: the protection is not required where it can be shown that leaving it out will not adversely affect the health or safety of building users, the intended use of the building, or the operation of building services. An unheated storage shed or an open parking structure are typical examples where the designer may make that case.
Standards for windows, doors and EIFS
Envelope materials installed to meet Part 5 must conform to the standards in the Part 5 standards table OBC Div. B 5.9.1.1.OBC Div. B 5.9.1.1. Compliance with Applicable Standards(1) Except as provided in Sentence (2) and elsewhere in this Part, materials and components, and their installation, shall conform to the requirements of the applicable standards in Table 5.9.1.1. where those materials or components are (a) incorporated into environmental separators or assemblies exposed to the…, but flame-spread ratings inside insulation standards apply only where Part 3 requires them.
| Element | What the code requires |
|---|---|
| Windows, doors, skylights | AAMA/WDMA/CSA 101/I.S.2/A440 (the Harmonized Standard) plus the CSA A440S1 Canadian Supplement; performance grades chosen for the location OBC Div. B 5.9.2.2.OBC Div. B 5.9.2.2. Applicable Standards(1) Windows, doors and skylights shall conform to the requirements in (a) AAMA/WDMA/CSA 101/I.S.2/A440, "North American Fenestration Standard/Specification for windows, doors, and skylights" (Harmonized Standard), and (b) CSA A440S1, "Canadian Supplement to AAMA/WDMA/CSA 101/I.S.2/A440-17, North American Fenestration… |
| Metal-framed glazing between conditioned and unconditioned or exterior space | A thermal break to minimize condensation, except storm units and fire-rated doors and windows OBC Div. B 5.9.2.4.OBC Div. B 5.9.2.4. Heat Transfer(1) Windows, doors and skylights shall meet the heat transfer performance requirements stated in Section 5.3. (See Note A-5.3.1.2.) (2) Except as provided in Sentence (3), all metal-framed glazed assemblies separating interior conditioned space from interior unconditioned space or exterior space shall incorporate a… |
| Curtain walls, window walls, storefronts | Air leakage not more than 0.2 L/(s x m²) for fixed parts and 1.5 L/(s x m²) for operable parts OBC Div. B 5.9.3.4.OBC Div. B 5.9.3.4. Air Leakage(1) Other fenestration assemblies and their components shall be designed and constructed in accordance with Section 5.4. (2) Except as provided in Sentence (3), other fenestration assemblies and their components shall have "Standard Test Method for Determining Rate of Air Leakage Through Exterior Windows, Curtain… |
| EIFS | Part 5 Sections 5.3 to 5.6 and CAN/ULC-S716.1 OBC Div. B 5.9.4.1.OBC Div. B 5.9.4.1. Structural Loads, Heat Transfer, Air Leakage, Vapour Diffusion and Water Penetration(1) Exterior insulation finish systems and their components shall comply with (a) Subsection 5.1.4. and Sections 5.3. to 5.6., and (b) CAN/ULC-S716.1, "Standard for Exterior Insulation and Finish Systems (EIFS) - Materials and Systems," where covered in the scope of that standard. (See Note A-5.9.4.1.(1)) |
"Other fenestration assemblies" is a defined phrase in this Subsection: curtain walls, window walls, storefronts and glazed architectural structures OBC Div. B 5.9.3.1.OBC Div. B 5.9.3.1. Definition(1) In this Subsection, "other fenestration assemblies" means curtain walls, window walls, storefronts and glazed architectural structures. (See Note A-5.9.3.1.(1)). Garage doors, revolving doors, commercial entrance systems, storm units, site-built doors and commercial steel doors are exempt from the air leakage limits. A wired glass assembly in a required fire separation need not meet the window Subsection at all.
Common traps
- Looking for an RSI value in Part 5. The Section is performance-based; numbers live in Part 12 and SB-10.
- Forgetting that the air barrier must be continuous at joints and penetrations, not only across the field of the wall.
- Picking S741 for an assembly. S741 is the material standard; S742 is the assembly standard.
- Applying the thermal break rule to a fire-rated window frame. Fire-rated units are exempt.
Chapter review
Chapter at a glance
One line per section: the idea to carry into the exam. Then the answers that most often catch candidates out.
- Heat transfer
Any component or assembly subject to an intended temperature differential must include materials that resist heat transfer, or a means to dissipate the heat.
- Air leakage and vapour diffusion
Precipitation: an exposed assembly must minimize ingress of rain into the assembly and prevent it reaching interior space.
- Standards for windows, doors and EIFS
Envelope materials installed to meet Part 5 must conform to the standards in the Part 5 standards table, but flame-spread ratings inside insulation standards apply only where Part…
Usual exam traps
- Looking for an RSI value in Part 5. The Section is performance-based; numbers live in Part 12 and SB-10.
- Forgetting that the air barrier must be continuous at joints and penetrations, not only across the field of the wall.
- Picking S741 for an assembly. S741 is the material standard; S742 is the assembly standard.
- Applying the thermal break rule to a fire-rated window frame. Fire-rated units are exempt.
Practice this chapter
Questions on Environmental separation (Part 5), in the exam format, every answer explained and cited to its article. Sign in to start; a free account gets the free questions.
Code cited in this chapter
Based on the official 2024 Building Code Compendium on ontario.ca.
© King's Printer for Ontario, 2024. Reproduced with permission.
OBC Div. B 5.3.1.1. Required Resistance to Heat Transfer
Open OBC Div. B 5.3.1.1. in the code viewer(1)Except as provided in Sentence (2), where a building component or assembly will be subjected to an intended temperature differential, the component or assembly shall include materials to resist heat transfer or a means to dissipate transferred heat in accordance with the remainder of this Subsection.
(2)The installation of materials to resist heat transfer in accordance with this Subsection is not required where it can be shown that uncontrolled heat transfer will not adversely affect any of
(a)the health or safety of building users,
(b)the intended use of the building, or
(c)the operation of building services.
OBC Div. B 5.3.1.2. Properties to Resist Heat Transfer or Dissipate Heat
Open OBC Div. B 5.3.1.2. in the code viewer(1)Taking into account the conditions on either side of the environmental separator, materials and components installed to provide the required resistance to heat transfer or the means implemented to dissipate heat shall provide sufficient resistance or dissipation,
(a)to minimize surface condensation on the warm side of the component or assembly,
(b)in conjunction with other materials and components in the assembly, to minimize condensation within the component or assembly,
(c)in conjunction with systems installed for space conditioning, to meet the interior design thermal conditions for the intended occupancy, and
(d)to minimize ice damming on sloped roofs. (See Note A-5.3.1.2.(1))
OBC Div. B 5.3.1.3. Location and Installation of Materials Providing Thermal Resistance
Open OBC Div. B 5.3.1.3. in the code viewer(1)Where a material required by Article 5.3.1.1. is intersected by a building assembly, penetrated by a high conductance component or interrupted by expansion, control or construction joints, and where condensation is likely to occur at these intersections, penetrations or interruptions, sufficient thermal resistance shall be provided so as to minimize condensation at these locations.
(2)Materials providing required thermal resistance shall have sufficient inherent resistance to airflow or be positioned in the assembly so as to prevent convective airflow through and around the material. (See Note A-5.3.1.3.(2))
OBC Div. B 5.4.1.1. Required Resistance to Air Leakage (Note A-5.4.1.1.)
Open OBC Div. B 5.4.1.1. in the code viewer(1)Where a building component or assembly separates interior conditioned space from exterior space, interior space from the ground, or environmentally dissimilar interior spaces, the properties and position of the materials and components in those components or assemblies shall be such that they control air leakage or permit venting to the exterior so as to
(a)provide acceptable conditions for the building occupants,
(b)maintain appropriate conditions for the intended use of the building,
(c)minimize the accumulation of condensation in and the penetration of precipitation into the building component or assembly,
(d)control heat transfer to roofs where ice damming can occur,
(e)minimize the ingress of airborne radon and other soil gases from the ground with an aim to controlling the indoor concentrations of these gases to an acceptable level, and
(f)not compromise the operation of building services.
(2)Except as provided in Sentence (7), an air barrier system shall be designed and constructed to provide the principal resistance to air leakage to meet the requirements of Sentence (1).
(3)The air barrier system shall incorporate air barrier assemblies that meet the appropriate Performance Class as defined in Table 5.4.1.1. (See Note A-5.4.1.1.(3))
(4)The air barrier system shall be designed and constructed to be continuous
(a)across construction, control and expansion joints,
(b)across junctions between different air barrier assemblies, and
(c)around penetrations through air barrier assemblies. (See Note A-5.4.1.1.(4))
(5)The structural design of air barrier assemblies, including junctions between air barrier assemblies, subject to air pressure loads shall comply with Article 5.1.4.1. and Subsection 5.2.2.
(6)The maximum air leakage rates specified in Table 5.4.1.1. are permitted to be increased where it can be shown that the higher rate will not adversely affect any of
(a)the health or safety of the building users,
(b)the intended use of the building, or
(c)the operation of building services.
(7)An air barrier system is not required where it can be shown that uncontrolled air leakage will not adversely affect any of
(a)the health or safety of building users,
(b)the intended use of the building, or
(c)the operation of building services. (See Note A-5.4.1.1.(7))
OBC Div. A 1.4.1.2.(1) Air barrier system
Open OBC Div. A 1.4.1.2.(1) in the code viewerAir barrier system means the assembly installed to provide a continuous barrier to the movement of air.
OBC Div. B 5.4.1.2. Air Barrier Assemblies
Open OBC Div. B 5.4.1.2. in the code viewer(1)Except as provided in Sentences (2) and (3), air barrier assemblies not in contact with the ground shall
(a)conform with CAN/ULC-S742, "Standard for Air Barrier Assemblies – Specification," and
(b)meet the selected Performance Class of Table 5.4.1.1. (See Note A-5.4.1.2.(1))
(2)Air barrier assemblies not evaluated in accordance with CAN/ULC-S742, "Standard for Air Barrier Assemblies – Specification," shall be designed and constructed
(a)to meet or exceed the selected Performance Class of Table 5.4.1.1., and
(b)with at least one air barrier material intended to provide the primary resistance to air leakage that meets the requirements of CAN/ULC-S741, "Standard for Air Barrier Materials – Specification." (See Note A-5.4.1.2.(2))
(3)Air barrier assemblies covered in Subsections 5.9.2., 5.9.3. and 5.9.4. shall meet the air barrier performance criteria defined in those Subsections.
(4)Below-grade air barrier assemblies in contact with the ground shall minimize the ingress of airborne radon and other soil gases. (See Note A-5.4.1.2.(4))
OBC Div. B 5.5.1.1. Required Resistance to Vapour Diffusion
Open OBC Div. B 5.5.1.1. in the code viewer(1)Where a building component or assembly is subjected to differentials in temperature and water vapour pressure, the properties and position of the materials and components in those components or assemblies shall be such that they control vapour diffusion or permit venting to the exterior so as to minimize accumulation of condensation in the building component or assembly.
(2)Except as provided in Sentence (3), a vapour barrier shall be installed to provide the principal resistance to water vapour diffusion.
(3)A vapour barrier is not required where it can be shown that uncontrolled vapour diffusion will not adversely affect any of
(a)the health or safety of building users,
(b)the intended use of the building, or
(c)the operation of building services.
OBC Div. B 5.5.1.2. Vapour Barrier Properties and Installation
Open OBC Div. B 5.5.1.2. in the code viewer(1)The vapour barrier shall have sufficiently low permeance and shall be positioned in the building component or assembly so as to
(a)minimize moisture transfer by diffusion, to surfaces within the assembly that would be cold enough to cause condensation at the design temperature and humidity conditions, or
(b)reduce moisture transfer by diffusion, to surfaces within the assembly that would be cold enough to cause condensation at the design temperature and humidity conditions, to a rate that will not allow sufficient accumulation of moisture to cause deterioration or otherwise adversely affect any of,
(i)the health or safety of building users,
(ii)the intended use of the building, or
(iii)the operation of building services. (See Note A-5.5.1.2.(1))
(2)Coatings applied to gypsum wallboard to provide required resistance to vapour diffusion shall conform to the requirements of Sentence (1) when tested in accordance with CAN/CGSB-1.501-M, "Method for Permeance of Coated Wallboard."
(3)Coatings applied to materials other than gypsum wallboard to provide required resistance to vapour diffusion shall conform to the requirements of Sentence (1) when tested in accordance with ASTM E96/E96 M, "Standard Test Methods for Water Vapor Transmission of Materials," by the desiccant method (dry cup).
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OBC Div. B 5.6.1.1. Required Protection from Precipitation
Open OBC Div. B 5.6.1.1. in the code viewer(1)Except as provided in Sentence (2), where a building component or assembly is exposed to precipitation, the component or assembly shall
(a)minimize ingress of precipitation into the component or assembly, and
(b)prevent ingress of precipitation into interior space.
(2)Protection from ingress of precipitation is not required where it can be shown that such ingress will not adversely affect any of
(a)the health or safety of building users,
(b)the intended use of the building, or
(c)the operation of building services.
OBC Div. B 5.9.1.1. Compliance with Applicable Standards
Open OBC Div. B 5.9.1.1. in the code viewer(1)Except as provided in Sentence (2) and elsewhere in this Part, materials and components, and their installation, shall conform to the requirements of the applicable standards in Table 5.9.1.1. where those materials or components are
(a)incorporated into environmental separators or assemblies exposed to the exterior, and
(b)installed to fulfill the requirements of this Part. (See Note A-5.9.1.1.(1))
(2)The requirements for flame-spread ratings contained in thermal insulation standards shall be applied only as required in Part 3.
OBC Div. B 5.9.2.2. Applicable Standards
Open OBC Div. B 5.9.2.2. in the code viewer(1)Windows, doors and skylights shall conform to the requirements in
(a)AAMA/WDMA/CSA 101/I.S.2/A440, "North American Fenestration Standard/Specification for windows, doors, and skylights" (Harmonized Standard), and
(b)CSA A440S1, "Canadian Supplement to AAMA/WDMA/CSA 101/I.S.2/A440-17, North American Fenestration Standard/Specification for windows, doors, and skylights."
(2)Performance grades for windows, doors and skylights shall be selected according to the Canadian Supplement referenced in Clause (1)(b) so as to be appropriate for the conditions and geographic location in which the window, door or skylight will be installed.
(3)Windows, doors and skylights shall conform to the performance grades selected in Sentence (2) when tested in accordance with the Harmonized Standard referenced in Clause (1)(a).
OBC Div. B 5.9.2.4. Heat Transfer
Open OBC Div. B 5.9.2.4. in the code viewer(1)Windows, doors and skylights shall meet the heat transfer performance requirements stated in Section 5.3. (See Note A-5.3.1.2.)
(2)Except as provided in Sentence (3), all metal-framed glazed assemblies separating interior conditioned space from interior unconditioned space or exterior space shall incorporate a thermal break to minimize condensation.
(3)Metal-framed glazed assemblies need not comply with Sentence (2) where these assemblies are
(a)storm windows or doors, or
(b)windows or doors that are required to have a fire-protection ratings. (See Note A-5.9.2.4.(3))
OBC Div. B 5.9.3.4. Air Leakage
Open OBC Div. B 5.9.3.4. in the code viewer(1)Other fenestration assemblies and their components shall be designed and constructed in accordance with Section 5.4.
(2)Except as provided in Sentence (3), other fenestration assemblies and their components shall have "Standard Test Method for Determining Rate of Air Leakage Through Exterior Windows, Curtain Walls, and Doors Under Specified Pressure Differences Across the Specimen," that is not greater than
(a)0.2L/(s × m^2) for fixed portions, including any opaque portions, and
(b)1.5L/(s × m^2) for operable portions. (See Note A-5.9.3.4.(2))
(3)The following systems need not comply with Sentence (2):
(a)interior windows and interior doors that do not serve as environmental separators,
(b)vehicular access doors (garage doors),
(c)storm windows and storm doors,
(d)commercial entrance systems,
(e)revolving doors,
(f)smoke and relief air vents,
(g)site-built door systems, and
(h)commercial steel doors. (See Note A-5.9.3.4.(3))
OBC Div. B 5.9.4.1. Structural Loads, Heat Transfer, Air Leakage, Vapour Diffusion and Water Penetration
Open OBC Div. B 5.9.4.1. in the code viewer(1)Exterior insulation finish systems and their components shall comply with
(a)Subsection 5.1.4. and Sections 5.3. to 5.6., and
(b)CAN/ULC-S716.1, "Standard for Exterior Insulation and Finish Systems (EIFS) - Materials and Systems," where covered in the scope of that standard. (See Note A-5.9.4.1.(1))
OBC Div. B 5.9.3.1. Definition
Open OBC Div. B 5.9.3.1. in the code viewer(1)In this Subsection, "other fenestration assemblies" means curtain walls, window walls, storefronts and glazed architectural structures. (See Note A-5.9.3.1.(1))