User's Guide: NBC 1995: Environmental Separation (Part 5)

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(1)Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. DRAFT COPY. User’s Guide – NBC 1995 Environmental Separation (Part 5). Issued by the Canadian Commission on Building and Fire Codes National Research Council of Canada.

(2) Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. DRAFT COPY. First Edition 1999. ISBN 0-660-17863-X NR36-1/1995-5E © National Research Council of Canada Ottawa World Rights Reserved NRCC 43409 Printed in Canada First Printing. Aussi disponible en français : Guide de l’utilisateur – CNB 1995, Séparation des milieux différents (Partie 5).

(3) DRAFT COPY. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. Table of Contents. Preface. ..................................... Section 5.1.. General ...................... 5.1.-1. Section 5.2.. Loads and Procedures ................ 5.2.-1. Section 5.3.. Heat Transfer ............ 5.3.-1. Section 5.4.. Air Leakage ............... 5.4.-1. Section 5.5.. Vapour Diffusion ........ 5.5.-1. Section 5.6.. Precipitation .............. 5.6.-1. Section 5.7.. Surface Water ........... 5.7.-1. Section 5.8.. Moisture in the Ground ....................... 5.8.-1. Appendix A. Processes of Deterioration .............. A-1. Appendix B. Constructability ......... B-1. Appendix C. Glossary of Terms, Symbols and Abbreviations ............. C-1. v. User’s Guide – NBC 1995 Environmental Separation (Part 5) [99/10/06@11:34]. iii.

(4) Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. DRAFT COPY. iv.

(5) DRAFT COPY. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. Preface. This User’s Guide discusses Part 5 as it appears in the National Building Code of Canada (NBC) 1995 and is intended to provide users with a better understanding of the requirements in Part 5. Increased knowledge of the objectives of the requirements, and the general principles on which they are based, will help the user comply with the NBC and ensure that the building envelope and other elements separating dissimilar environments meet the required performance levels. NBC Part 5, Environmental Separation, provides the requirements for the design and construction, or selection, of those elements of the building intended to separate dissimilar environments, primarily those of the building envelope. It also provides the requirements for site conditions that may affect moisture loading on the building envelope. The intent is to address health and safety by setting minimum requirements for environmental separators to function adequately (by resisting or accommodating the loads imposed by the environments to which they are exposed), and by requiring that they resist deterioration to fulfil that function for the design service life of the separator. Improper design, construction, interfacing, or selection of building materials and assemblies may result in either inadequate separation of environments or the premature deterioration of the separator elements and adjacent materials and components, both of which can lead to unsafe or unhealthy conditions. The requirements also have an impact on energy consumption, influence the level of occupant comfort, and help ensure proper operation of building services.. Section 5.1. addresses resistance to environmental loads and the durability of the materials that must be installed to control and resist such loads. Section 5.2. identifies the information and methods necessary for calculating the loads created by the driving forces, as well as the resistance required to ensure that the control measures will perform adequately. Sections 5.3. to 5.8. provide those requirements for resistance to specific conditions that are considered critical to the performance of the separator. Achieving an effective environmental separation depends on effective interaction, communication and cooperation among all the participants in the design and construction process. The section on Durability, Quality Management and Constructability in Resistance to Deterioration [5.1.4.2.] in this User’s Guide, highlights these important considerations. This User’s Guide has no legal status and is not intended for formal adoption; its purpose is solely informational. Sketches and diagrams are presented to illustrate principles only. They are not design or construction details. Other methods of satisfying the intent of the NBC requirements may also be valid. The words and terms in italics in this User’s Guide have the meanings provided in Appendix C, Glossary of Terms, Symbols and Abbreviations.. Although the concepts apply to all buildings, Part 5 requirements apply to buildings other than those covered by Part 9, Housing and Small Buildings. If Part 5 requirements are applied to renovations of existing buildings, care must be exercised, because not all aspects of Part 5 may be applicable. Changing the interior environmental conditions in old or historical buildings can have detrimental effects on building envelopes, particularly those constructed using mass masonry.. User’s Guide – NBC 1995 Environmental Separation (Part 5) [99/10/06@11:34]. v.

(6) DRAFT COPY. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. Acknowledgements This User’s Guide was first drafted as a Commentary for the NBC 1990, by a team of researchers from the Institute for Research in Construction of the National Research Council under the direction of a Task Group reporting to the Standing Committee on Structural Design, the committee responsible at that time for Part 5. John Gibson, Consultant, revised the Commentary on Part 5, Wind, Water and Vapour Protection, National Building Code of Canada 1990, for application to the NBC 1995, under the direction of a Task Group reporting to the Standing Committee on Environmental Separation. The Task Group members were: D. Clancey (Chair) M.D. Lawton R. Oliver A. Patenaude G.R. Sturgeon W.C. Brown (Research Advisor) G.A. Chown (Technical Advisor) The resulting User’s Guide was reviewed by: R. Eastwood J.R.S. Edgar G.J. Foley M.J. Frye D. Hamilton G. Lowes B. Phillips G. Proskiw D.R. Ricketts R. Trempe R. Wilson The French edition was further reviewed by: R.L. Blanchette A. Patenaude M.V. Petrone G.F. Poirier M.Z. Rousseau. vi. Final decisions on the content of this User’s Guide were the responsibility of the Canadian Commission on Building and Fire Codes, on the recommendation of the Standing Committee on Environmental Separation. The Standing Committee had the following membership: R.M.B. Johnson (Chair) R.L. Blanchette D. Clancey K.A. Coulter J.R.S. Edgar J.S. Frain J. Gibson R.F. Gray G.F. Johnson R.M. Kobrick R.L. Maki M.M. Parker A. Patenaude M.V. Petrone M. Rickard D. Stones G.R. Sturgeon D. Surry C.M. Tye W.C. Brown (Research Advisor) G.A. Chown (Technical Advisor) Comments on this document are welcome and should be sent to: The Secretary Canadian Commission on Building and Fire Codes Canadian Codes Centre Institute for Research in Construction National Research Council of Canada Ottawa, Ontario K1A 0R6. [99/10/06@11:34] User’s Guide – NBC 1995 Environmental Separation (Part 5).

(7) DRAFT COPY. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. Section 5.1. General Scope [5.1.1.1.] According to Section 2.1. of the National Building Code of Canada (NBC), Part 5 applies to: (a) all buildings used for major occupancies classified as: (i) Group A, assembly occupancies, (ii) Group B, care or detention (institutional) occupancies, or (iii) Group F, Division 1, high hazard industrial occupancies, and (b) all buildings exceeding 600 m2 in building area or exceeding 3 storeys in building height used for major occupancies classified as: (i) Group C, residential occupancies, (ii) Group D, business and personal services occupancies, (iii) Group E, mercantile occupancies, or (iv) Group F, Division 2 and 3, medium and low hazard industrial occupancies. Essentially, Part 5 applies to all buildings not covered by Part 9, Housing and Small Buildings. Because the principles of physics are the same regardless of building size and occupancy, the concepts on which Part 5 requirements are based are equally valid for Part 9 buildings. Part 9 contains minimum requirements for smaller buildings, which may be subject to loads that are less onerous than those imposed on larger or taller buildings. In many cases, therefore, Part 9 requirements are not applicable to buildings covered by Part 5.. Application [5.1.2.] The primary focus of Part 5 is the control of moisture movement through or on those parts of the building that separate dissimilar environments, including those that separate the interior environment from the ground. Other concerns relate to wind or soil gas penetration, heat and air transfer, structural loads and deterioration. Moisture from construction materials and processes is not specifically addressed. While Part 5 is not limited to the exterior building envelope, the majority of the requirements, such as. the control of groundwater and the penetration of wind and rain, can only apply to the parts of the building that separate the interior from the exterior environment. Nevertheless, where applicable, and especially with respect to moisture, the requirements of Part 5 are also intended to apply to separators of dissimilar interior environments. An example of where such an interior separator would be required is in a sports centre, between the swimming pool and the ice arena. Frequently, exterior building elements, such as decorative columns, walls, balcony decks or guards, exist that are not environmental separators. For these, the requirements of NBC Section 5.6., Precipitation, should be considered, to resist damage to materials.. Definitions [5.1.3.] Words that appear in italics in the NBC are defined in Part 1 of the NBC. For words that appear in italics in this User’s Guide, refer to Appendix C, Glossary of Terms, Symbols and Abbreviations.. Resistance to Environmental Loads [5.1.4.1.] Environmental loads refer to loads on materials, components or assemblies exposed to: • wind pressures; • precipitation; • thermal variances; • solar radiation; • moisture as vapour in air; • air pressure differentials created by temperature difference (stack effect and convection) or by mechanical fan systems; • water pressure created by moisture in the ground, or a standing head of water against an enclosure; • structural stresses, deflections and differential movements caused by live and dead loadings, wind, earthquakes, shrinkage, creep, settling, thermal variations, vibration and impact;. User’s Guide – NBC 1995 Environmental Separation (Part 5) [99/10/06@11:34]. 5.1. - 1.

(8) General. DRAFT COPY. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. • electrochemical and chemical attack (e.g. from pollutants such as acid rain); • biological attack by living organisms and their by-products. A separator must be designed and constructed to resist or accommodate all loads that may be reasonably expected to occur within the environment in which it is to function. Environmental and structural loads are interrelated, since one load may create the other load, which must be resisted or accommodated. The structural requirements of Part 4 of the NBC address peak loads; Part 5 also addresses sustained loads. Because it is vital to many mechanisms of deterioration, moisture is recognized as the environmental load with the most potentially wide-ranging adverse consequences. See also Resistance to Deterioration [5.1.4.2.], below.. Wind Control of air flow induced by wind is discussed in this User’s Guide both in the context of controlling the transfer of moisture (Section 5.4.), and in terms of wind damage to roofs (Section 5.6.). Impact loads related both to the use of the building and to wind-borne debris should be considered, in terms of the likelihood of occurrence as well as the resistance of the materials and components in the assembly.. Accommodating Movement and Deformation. Moisture Part 5 is primarily directed at reducing moisture movement into or through the building envelope in order to minimize damage and reduce the likelihood of failure due to moisture accumulation. Moisture can be transported through building materials and assemblies by any combination of the following mechanisms: • water vapour diffusion driven by water vapour pressure difference; • moist air flow driven by air pressure difference; • liquid water flow driven by surface tension (including capillary), gravity (including hydrostatic pressure), air pressure difference (wind or mechanical) or kinetic energy (rain drop momentum). The net effect of these moisture flows, including condensation of moisture on cold surfaces that are below the dew point temperature of the ambient air, combined with the effects of venting and drainage, determines the rate of moisture deposition and drying at any place in the assembly. Various building assembly designs can prevent, or at least minimize, moisture accumulation in the assembly. The first step is to control moisture movement into the assembly. A design must control moisture movement and accumulation due to: • insufficient heat transfer resistance (NBC Section 5.3.); • air leakage (NBC Section 5.4.); • vapour diffusion (NBC Section 5.5.); • ingress of precipitation (NBC Section 5.6.); • ingress of surface water (NBC Section 5.7.); • ingress of moisture in the ground (NBC Section 5.8.). 5.1. - 2. In view of the likelihood that these preventive measures will not function perfectly, this control should be supported by venting and/or drainage to limit accumulation and expedite drying of the assembly.. The building envelope must accommodate both permanent and cyclic movement and deformation. The former may occur due to initial settling and long-term creep of the structure, as well as shrinkage of materials as they dry. The latter may occur due to loading from wind, earthquakes, occupancy and use, intermittent thermal or moisture stresses, or fluctuating hydrostatic loads. Because many materials have limited elasticity to absorb these movements, they must be accommodated at joints and junctions. Proper joint and junction design requires a prediction or measurement of expected movement, including direction and amplitude. These depend on the nature of the materials involved, the environmental and structural loads imposed on them, and the geometry of the components and anchorage method. Where the environmental separator bridges a joint or junction in the structure or backup, care must be taken to ensure continuity of critical elements such as the air barrier system and insulating materials. Materials selected to bridge joints and junctions must be capable of accommodating movement without failure of the material or configuration. A building envelope component may be: • an inherent part of a structural component and thus self-supporting; • adhered; or • mechanically fastened. Except in the first case, positive securement and allowance for movement are primary considerations. The most vulnerable parts of an environmental separator are the joints and junctions because of the movement they must accommodate. These meetings. [99/10/06@11:34] User’s Guide – NBC 1995 Environmental Separation (Part 5).

(9) General. DRAFT COPY. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. of materials and assemblies are discussed throughout the User’s Guide as they pertain to the requirements of the various sections. Movement, stresses induced by movement, and measures taken to accommodate movement are concerns of both Part 4 and Part 5 of the NBC. The primary structure should not induce stresses on the environmental separator, and loads must be carried from the environmental separator to the primary structure.. Resistance to Deterioration [5.1.4.2.] Durability is the ability to resist or accommodate agents and mechanisms of deterioration in the service environment in order to perform, over time, the required functions at or above a minimum level. The materials, components and assemblies that serve environmental separation functions must be designed or selected, and installed, in such a way as to be durable. Building elements that have a design service life less than that of the building or the assembly of which they form a part, should be designed to be accessible to allow inspection, repair or replacement as part of the building maintenance requirements. The ability of a building element to perform its intended function depends both on the properties of the element and on the environment in which it is intended to function. The elements should be selected, or their properties or characteristics specified, with their respective environments in mind. These include conditions during construction, and environmental and structural loads in situ. The compatibility of adjoining materials must be assessed, since two materials in contact may experience deterioration as a result of chemical interaction. Examples of chemical incompatibility include: galvanic corrosion between dissimilar metals; deterioration of plastics in contact with some sealants; corrosion of steel and zinc in contact with wood containing certain preservative chemicals; and corrosion of lead and some aluminum alloys in contact with moist concrete. Accelerated testing may be required to determine the service life of materials under expected conditions. Among those deterioration processes that must be considered are: hygrothermal (dealing with moisture and heat); chemical; electrochemical; biochemical; and biological. Information on these environmental factors, corrosion of fastening devices and cathodic protection against corrosion are all presented in Appendix A. See also CSA standard S478-95, “Guideline on Durability in Buildings.”. Durability, Quality Management and Constructability In the quest to achieve durability, an important factor can be an effective quality management program, which should be implemented from the initiation of a construction project. Its objective would be to ensure that all quality assurance checks are conducted, and that corrections are made if the specified quality is not met. As part of quality assurance, testing of pre-built or mocked-up portions of an assembly can help determine construction sequencing and the overall performance as constructed. The success of an environmental separator depends not only on the properties and functions of the materials and components being installed, but also on an overall co-ordinated approach to design and construction. Effective design and construction practices demand interaction, communication and co-operation among a number of participants who have different areas of expertise and different levels of knowledge and skill. Building projects benefit when designers, constructors, manufacturers and suppliers work as a team from the outset, developing a common vision and understanding of the intended product and the processes required to achieve that product. A team must have a common understanding of design intent, prevalent or preferred construction practices, the constructability of the building envelope details, and the quality of workmanship to be provided. See Appendix B and CSA standard S478-95, “Guideline on Durability in Buildings.”. Exceptions [5.1.4.2.(2)] Throughout Part 5 there are exceptions to the basic requirements. These are permitted only where design and construction to criteria different than those otherwise stated will not adversely affect: (1) health and safety, which are the principle purposes of the NBC; (2) intended building use (recognizing that the function of the facility must be considered); or (3) operation of building services (recognizing that the health, safety and functionality of the facility depend on plumbing, heating, cooling, ventilation and fire protection systems). Exceptions are provided to allow for construction of buildings for specific occupancy, location, building materials, etc., which may not need strict adherence to the requirements of Part 5. For example, temporary buildings may not provide the resistance to deterioration generally required by NBC Article 5.1.4.2. A stadium may have some moderation of temperature within it, but not provide the resistance to heat transfer, air leakage or. User’s Guide – NBC 1995 Environmental Separation (Part 5) [99/10/06@11:34]. 5.1. - 3.

(10) General. DRAFT COPY. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. precipitation required in NBC Sections 5.3., 5.4. and 5.6. When exceptions are invoked, the intent is generally to exempt all subsequent provisions in the respective sections. There is only one case where general exemption does not apply; this is related to wind uplift on roofs. Invoking the exceptions may require verification that there are no adverse affects associated with the three criteria listed above. Tests and calculations necessary to verify acceptable performance may prove difficult to identify.. Equivalency. Requirements in Other Parts of the NBC [5.1.5.1.] Materials, components and assemblies that are included in buildings to meet the requirements of Part 5 must also meet the requirements of other parts of the NBC, including the fire and acoustical provisions of Part 3 and the structural requirements of Part 4.. Supplemental Reading. The user should not confuse these exception provisions with equivalency allowed for in Section 2.5. of the NBC. The exceptions provide for situations where a level of performance less than that which is generally required may be appropriate. Equivalency can be invoked when the intent of the NBC requirements can be met with an alternative approach that provides the same or equivalent level of performance.. (1). (2). Burge, H., Su, J. and Spengler, J., Moisture, Organisms and Health Effects, Moisture Control in Buildings, ASTM MNL 18, American Society for Testing and Materials, West Conshohocken, Pennsylvania. CSA standard S478-95, Guideline on Durability in Buildings, Canadian Standards Association, Etobicoke, Ontario.. Occupant Health and Safety The requirements of Part 5 have objectives for occupant health in the indoor environment. Some implications of failing to meet the requirements are: • Accumulated moisture may support mould and mildew growth. This can contribute to poor indoor air quality from airborne spores and bacteria, which can cause illness. Material degradation may also occur, including damage to finishes or the building structure. • Infiltration can amplify the effects of mould and mildew in indoor air where the deterioration is within the environmental separator. It can also bring additional problems from soil gases such as radon and methane, and from outdoor air pollutants such as exhaust fumes from vehicles. • Infiltration can also produce unacceptable thermal conditions if it leads to cold drafts in the occupied space. Objectives related to safety are intended to minimize the harm that might result from hazards such as: • Ice or snow falling off roofs. • Materials falling from the building due to failure of fastening devices that is caused by corrosion. • Freezing of critical services such as fire suppression sprinkler piping, caused by infiltration of cold air. • Degradation of structural strength due to rotting or rusting caused by the presence of water trapped within an assembly. 5.1. - 4. [99/10/06@11:34] User’s Guide – NBC 1995 Environmental Separation (Part 5).

(11) DRAFT COPY. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. Section 5.2. Loads and Procedures Scope Section 5.2. of the NBC addresses the loads and calculation procedures that must be considered when selecting building envelope materials and components in order to ensure that those materials and components ultimately perform the functions for which they were intended. All components in roof, wall and floor separation assemblies, both above and below grade, are to be considered. The loads to be considered are those created by exterior environmental conditions and interior design conditions. Information on climatic conditions, found in Appendix C of the NBC, includes: • winter and summer design temperatures; • rainfall; • snow; • wind pressure; and • seismic loadings. Other exterior conditions that should be considered include: • humidity; • airborne salts and other pollutants; and • ultraviolet radiation. The interior design conditions determined by the building program include: • temperature; • humidity; and • air pressures caused by mechanical fan systems or stack effect. For smaller, simpler buildings, Part 9 of the NBC provides specific requirements for the selection and installation of building envelope elements. Considerable information on the subject is available for smaller buildings.(1)(2) Buildings covered by Part 5 may be larger or more complex, or subject to more severe structural or environmental loads. In these cases, more stringent requirements may be necessary. Some design information is provided in the appendices to the NBC, in various material and installation standards provided in Part 5, and in references provided in sections of this User‘s Guide.. Exterior Environmental Loads [5.2.1.1.] Refer to Section 2.2. and Appendix C of the NBC for detailed values required for the determination of exterior environmental loads. Other such loads not included in Appendix C are humidity, solar radiation and airborne road and sea salt. A major concern is the water load created by winddriven rain on exterior walls. This is particularly true in coastal locations, not because the driving rain wind pressures (DRWP) are necessarily higher in coastal areas, but because these regions have higher annual rainfalls and consequently higher annual driving rain indices (ADRI). Water can accumulate in cavities and on horizontal surfaces, testing the perfection of joints and junctions. DRWP data is published in CSA A440.1-M1990, “User Selection Guide to CAN/CSA-A440-M90 Windows,” and is available from Environment Canada. ADRI data can be found in CSA A370-94, “Connectors for Masonry.” Theoretically, soil temperature data are required to design a separation below grade, however, it is usually adequate to follow good practice that has been proven successful in a particular area.. Interior Environmental Loads [5.2.1.2.] Interior heat, air and moisture loads can be determined from the building program requirements and the mechanical design.(3) It is advisable to state the interior design conditions and the limitations of the design in the design documents. Consideration must also be given to uncontrolled relative humidity levels. Indoor air relative humidity can rise for a number of reasons, including shut-down for maintenance or repair of ventilation or dehumidification equipment, carpet steam cleaning, or the existence of a cold basement when outdoor conditions are warm and humid.. User’s Guide – NBC 1995 Environmental Separation (Part 5) [99/10/06@11:34]. 5.2. - 1.

(12) Loads and Procedures. DRAFT COPY. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. Structural Loads within Assemblies Although Section 5.2. of the NBC does not refer to the structural loads discussed in Section 5.1. of this User’s Guide, these loads should be considered in the design of an environmental separator. For example, in an exterior wall, long-term creep can over-compress a joint that was designed only for thermal expansion.. Calculation Procedures [5.2.2.1.] Reference is made to the ASHRAE Handbook(3) as providing examples of good practice in calculating air, moisture and heat transfer. Other methods may also be acceptable. Part 4 of the NBC provides detailed information about design procedures and methods to calculate the magnitude of structural loads. Additional information is provided by CSA design and materials standards, structural design handbooks and product manufacturers’ literature.. References (1) (2) (3). 5.2. - 2. National Housing Code of Canada 1998 and Illustrated Guide, NRCC 42803, National Research Council Canada, Ottawa. High-Rise Residential Construction Guide, 1995 edition, Ontario New Home Warranty Program, Toronto. ASHRAE 1997 Handbook — Fundamentals, SI edition, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta, Georgia.. [99/10/06@11:34] User’s Guide – NBC 1995 Environmental Separation (Part 5).

(13) DRAFT COPY. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. Section 5.3. Heat Transfer Required Resistance to Heat Transfer [5.3.1.1.]. Properties To Resist Heat Transfer [5.3.1.2.]. Where a temperature difference is intended by the design requirements, control of heat transfer is required by Part 5. The mechanisms of heat transfer are: conduction, convection, radiation and mass transfer.. Materials and components installed in an environmental separator are required to provide adequate resistance to heat transfer to minimize condensation within the component or assembly or on the surface of its warm side. It is also required that these materials and components, in conjunction with the space-conditioning systems, permit the maintenance of the interior design thermal conditions. This requirement suggests that the thermal resistance of insulating materials must be selected in conjunction with the sizing of any heating and air-conditioning systems.. Part 5 does not address minimum requirements for energy efficiency. Reference can be made to the Model National Energy Code of Canada for Buildings (MNECB) 1997.(1) Materials to resist heat transfer are required to minimize condensation on or within a separator assembly and to meet interior design thermal conditions where such condensation or lack of control of interior temperatures will adversely affect health and safety or the intended use of the building, or the operation of the building services.. Exceptions [5.3.1.1.(2)] Heat transfer need not be controlled for an unconditioned structure since a temperature differential across the separation is not intended by design. Under this condition, there would be no required thermal resistance for the separator. Where there is an intended temperature differential, under certain conditions, the Part 5 requirements to control condensation and temperature conditions may be satisfied—without need for supplementary materials to improve resistance and control heat transfer—by the thermal resistance inherent, for example, in a plywood or gypsum board sheathing. An example of this would be an assembly located in a building that is exposed to moderate exterior environments and whose intended use requires minimal separation, such as a warehouse maintained just above freezing. Another example would be an interior wall placed as the separation between two spaces subjected to minimal design temperature and humidity differences. See Exceptions [5.1.4.2.(2)] in Section 5.1. of this User’s Guide.. To meet the requirements of Section 5.1. of the NBC, materials selected to provide the major thermal resistance within an assembly must also be able to resist other environmental loads or be protected and supported by other elements that provide the necessary resistance. Some materials, such as those in a protected membrane roof assembly, may be exposed to moisture in the form of precipitation. Others may be required to resist structural loads such as compression due to deflection of a membrane under wind loads, or the dead and live loads under a slab on ground. In many designs it is assumed that some moisture can form, may accumulate within the assembly, and will be drained or vented out. Up until the end of the design service life, the materials selected must be able to accommodate this moisture without either failing due to degradation over time or supporting biochemical attack. Fasteners should be designed or selected to resist corrosion, and to avoid deforming or compressing the materials intended to resist heat transfer. Adhesives should have a design service life not less than the design service life of the assembly of which they are a part, and be suitable for the substrate conditions given the construction environment and tolerances expected. For example, substrates should be within the temperature range recommended by the manufacturer, and substrate materials should be flat enough to allow thorough contact of the. User’s Guide – NBC 1995 Environmental Separation (Part 5) [99/10/06@11:34]. 5.3. - 1.

(14) Heat Transfer. DRAFT COPY. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. adhesive with the substrate and the materials being adhered. With the exceptions of storm or fire-rated doors and windows, all metal-framed glazed assemblies in environmental separators are required to have a thermal break.. Standards [5.3.1.2.(2)] In Part 5, material and component standards and installation standards are invoked only where materials and components covered by the scope of the standards listed are used. This allows designers freedom to choose materials and components other than those included in available standards, and other than those included in the standards listed in Part 5. Section. Location and Installation of Materials Providing Thermal Resistance [5.3.1.3.] It is important to consider the movement of moisture from the indoor air to colder surfaces on the interior or within the envelope assembly. Interior surfaces of assemblies with inadequate thermal resistance may be sufficiently cold to allow surface condensation, possibly leading to deterioration, and growth of fungi and moulds. Assemblies can also be subject to interstitial condensation if there is inadequate thermal resistance on the cold side of the elements that control the vapour diffusion (see also Section 5.4. of the NBC and Guide). The effectiveness of insulating materials can be considerably reduced by compression of the materials and by thermal bridges created by the penetration of materials that have high thermal conductance, such as metal studs, structural joists or metal supports. See Figure 5.3.-1. Temperatures of surfaces and within assemblies should be calculated and the design adjusted as necessary to avoid excessive condensation. In hygroscopic materials, moisture may accumulate even where the surface temperature is above the dew point temperature of the adjacent air. For example, it has been demonstrated in the laboratory that gypsum-based and wood-based materials can accumulate measurable quantities of moisture when the relative humidity of the air adjacent to the material is no more than 80%. Since this condition may produce corrosion, rotting and general decay at temperatures higher than the dew point, care should be taken to ensure that temperatures are sufficiently high, and moisture conditions sufficiently low, to minimize moisture accumulation. 5.3. - 2. Plan. EC01096A. Figure 5.3.-1 Thermal bridges through floor slab, window frame, brick angle and metal studs Joints provided to accommodate movement in assemblies can interrupt the continuity of the insulating materials. Junctions between assemblies such as basement walls and above-ground walls, walls and roofs, and walls and window frames, can also create discontinuities in the thermal resistance. Special details to provide either thermal breaks or the necessary thermal resistance around such discontinuities are frequently required to minimize condensation. These can take the form of: • adding additional insulation on the exterior of stud flanges; • insulating a penetrating steel member for some distance on the interior; • providing thermal breaks on fasteners and frames; and • extending insulation up and over parapets or roof expansion joints. The construction of concrete block firewalls through roofs, and cantilevered concrete balconies can increase the potential for condensation on the. [99/10/06@11:34] User’s Guide – NBC 1995 Environmental Separation (Part 5).

(15) Heat Transfer. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. DRAFT COPY interior surfaces. The firewall can be insulated for some distance on the inside, and the block cores sealed where the wall penetrates the roof insulation, to avoid convective air movement. The balcony may be provided with a thermal break at the insulation plane of the wall, or the interior floor may be insulated above and below to avoid condensation. Ideally, the plane of insulation should surround the building, outboard of the air barrier system and structure, thus reducing thermal bridges to only those required for fasteners or supports for the exterior finishes, and also reducing thermally induced movement of the structure. Research(2)(3) has shown that insulating materials installed with a small air space between them and their substrate, on the warm side, can lose a high. proportion of their thermal resistance due to convection air movement around or through the material. It is required that the material either has a resistance to air flow, making it the principal airtight element of the air barrier system (see NBC Article 5.4.1.2.), or is installed in full and continuous contact with a component that has low air permeance. Another mechanism that can reduce the resistance to heat transfer is the movement of air through fibrous insulating materials, caused by wind. Air may move through the porous materials if there are openings in the exterior finish positioned in such a way that air may move into and back out of assemblies. See Figure 5.3.-2.. short-circuiting behind insulation. Section. short-circuiting controlled by low air permeance material in continuous contact with insulation. Plan EC01097A. Figure 5.3.-2 Short-circuiting past thermal insulation. User’s Guide – NBC 1995 Environmental Separation (Part 5) [99/10/06@11:34]. 5.3. - 3.

(16) Heat Transfer. DRAFT COPY. Supplemental Reading. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. (1). Drysdale, R.G. and Suter, G.T., Exterior Wall Construction in High-rise Buildings, Canada Mortgage and Housing Corporation, Ottawa, 1991.. References (1) (2). (3). 5.3. - 4. Model National Energy Code of Canada for Buildings 1997, NRCC 38731, National Research Council Canada, Ottawa. LeCompte, J.G.N., Influence of Natural Convection in an Insulated Cavity on the Thermal Performance of a Wall, Insulation Materials, Testing and Applications, ASTM 1030, American Society for Testing and Materials, West Conshohocken, Pennsylvania. Brown, W.C., Bomberg, M.T., Ullett, J.M. and Rasmussen, J., Measured Thermal Resistance of Frame Walls with Defects in the Installation of Mineral Fibre Insulation, Journal of Thermal Insulation and Building Envelopes, Volume 16, April 1993, National Research Council Canada, Ottawa.. [99/10/06@11:34] User’s Guide – NBC 1995 Environmental Separation (Part 5).

(17) DRAFT COPY. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. Section 5.4. Air Leakage Required Resistance to Air Leakage [5.4.1.1.] In general, an environmental separator is required to have an air barrier system to control air leakage. Air leakage is uncontrolled air flow through a building element. Infiltration is air leakage into a building, while exfiltration is air leakage out of a building. Air leakage may also occur between two interior spaces. Air leakage is unplanned and can lead to a number of undesirable consequences. Those causing the most frequent concern are the deposition of moisture within the building assembly from exfiltration, and rain penetration carried by infiltration driven by wind. In both cases, this moisture can produce problems ranging from surface staining to premature deterioration of the assembly. Air leakage, and the holes associated with it, can also have detrimental effects on the indoor environment, including: • difficulty in controlling temperature and humidity; • entry of polluted air such as soil gases or vehicle exhaust; • excessive transmission of exterior noise; • increased energy consumption; • freezing of water pipes; • fire-related problems, such as increased fire spread and diminished smoke control; and • noise and door-operation problems created by stack effect (see sidebar). These detrimental effects can occur in any building unless due care is exercised in design and construction. Air leakage must be controlled if. differentials of temperature, water vapour pressure and air pressure exist in combination: • A temperature differential will exist in the heating or cooling seasons. • A water vapour pressure differential could exist because the occupants and their activities add moisture to the interior air; mechanical humidification may further increase the moisture load. • An air pressure differential will be generated by the temperature differential (referred to as stack effect or chimney effect), by mechanical ventilation, and by wind. All three differentials can be expected to exist in an occupied building, where the space is conditioned (particularly in Canada in the winter), and therefore the requirements of Section 5.4. of the NBC will apply to most buildings covered under the scope of Part 5. See Figure 5.4.-1.. Stack Effect The same difference in pressure that drives warm air up a chimney or smoke stack drives warm air upward through the interior of a heated building. As air is heated, it expands and becomes less dense. Where there are intentional or unintentional openings through the building envelope, the warm air will escape through the higher openings above the neutral pressure plane and be replaced by colder air entering through lower openings below the neutral pressure plane. In the absence of openings other than at the bottom, the difference in pressure will create a positive pressure on the interior of the envelope above the neutral pressure plane, though there would be no airflow.. User’s Guide – NBC 1995 Environmental Separation (Part 5) [99/10/06@11:34]. 5.4. - 1.

(18) DRAFT COPY neutral pressure plane. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. Air Leakage. permeance or porous materials. The intent of Section 5.4. of the NBC is to produce environmental separators that control air leakage to a degree sufficient to preclude initiating moisture-related deterioration due to condensation or precipitation ingress, to limit drafts and pollutant transfer, and to permit control of indoor air and surface temperatures and indoor relative humidity.. wind effect. Air Leakage and Ventilation Although air leakage has been relied upon in the past to provide ventilation for the occupants and processes in buildings, this approach is highly weather dependent and is now generally recognized as inefficient, unreliable and often ineffective. Reliance on air leakage becomes completely ineffective when the airtightness requirements are met. Although natural ventilation by means of venting windows can sometimes be used during mild weather, mechanical systems are generally installed to provide the required volumes of fresh air when and where such air is needed. Ventilation requirements for buildings covered by Part 5 are addressed in Part 6 of the NBC.. neutral pressure plane. stack effect. Air Leakage and Vapour Diffusion. neutral pressure plane. Two mechanisms that move water vapour from an interior space into the building envelope or into an assembly separating dissimilar interior environments are: • vapour diffusion (movement at the molecular level through building materials). See NBC Section 5.5.; and • air leakage (transporting moisture as vapour through openings in or between materials).. mechanical ventilation effect. ne. utr. al. pr. es. su. re. The vapour barrier, the material providing the principal resistance to vapour diffusion, must have low vapour permeance. Similarly, the material providing the principal resistance to air leakage must provide low air permeance. There are many materials used in assemblies that have the properties necessary to fulfil both functions. Examples are glass, sheet metal and roofing membranes.. pla. ne. combined effect EC01098A. Figure 5.4.-1 Forces inducing air leakage Although there is almost always enough of an air pressure differential to drive air leakage, leakage will only occur if there are holes in the building envelope through which the air can flow. Such holes do not have to run straight through the envelope, but rather could consist of a path resulting from a combination of gaps in or between low permeance materials and the many small holes in high 5.4. - 2. In cold climates, air leakage is usually the culprit when condensation problems within environmental separators are investigated. The reason for this is that the quantity of moisture that can be driven by diffusion through even a discontinuous vapour barrier is very low, and can frequently be accommodated by the assembly. Where moisture is deposited by air leakage, the volumes are considerably greater, due to the high moisture content of the interior air, and because all of the condensation occurs near the location of the opening in the airtight element of the air barrier. [99/10/06@11:34] User’s Guide – NBC 1995 Environmental Separation (Part 5).

(19) Air Leakage. DRAFT COPY. 35. Control of air leakage is achieved with low air permeance materials assembled with low permeance joints. Because air leakage is driven by an air pressure difference and the loads generated by that difference must be resisted by the air barrier system, the system must have the structural integrity to accommodate wind gust loads. Stack effect and mechanically induced pressures are relatively minor.. 15. Air barrier systems should have a service life at least as long as that of the assembly in which they are installed or they should be repairable or replaceable. Where the service life of the envelope assembly is less than that of the building, the assembly should be repairable or replaceable and the costs known. The building envelope should incorporate an effective air barrier system throughout the life of the building.. 10. Air Leakage Limit for Air Barrier Systems. 30. Water Vapour Flow, mg/s. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. system. See Figure 5.4.-2. This does not mean that the vapour barrier can be ignored; it does mean that the quality assurance of the air barrier system should be paramount throughout the design and construction process.. Moisture transferred by air leakage. 25 20. 5. Moisture transferred by vapour diffusion. 0 0.001. 0.01. 0.1. 1. 10. Airflow, L/s EC02004A. Figure 5.4.-2 Moisture transfer through untreated interior gypsum board, due to vapour diffusion versus air leakage at an interior temperature of 21 C and relative humidity (RH) of 35%, and an exterior temperature of -25 C and RH of 50% Air leakage can play a role in rainwater ingress by reducing pressure equalization in the cavity of a rainscreen wall. See Section 5.6., Precipitation, of this Guide.. Exceptions [5.4.1.1.(2)] See Exceptions [5.1.4.2.(2)] in Section 5.1. of this User’s Guide.. Air Barrier System Properties [5.4.1.2.] To meet the intent of Section 5.4. of the NBC, the barrier to air leakage, or the air barrier system, should exhibit a number of functional characteristics.(1) These include: • low air permeance; • continuity; • structural integrity; and • durability.. The requirement for an air barrier system does not imply a perfect barrier. An effective air barrier system is considered to be one that is close enough to perfection to prevent condensation problems. The majority of Canadian buildings do not suffer negative effects from condensation, even though their air barrier systems fall short of perfection and some condensation occurs within the building assembly. Experience has shown that where the indoor humidity is controlled to reasonable levels in winter and the building is not subject to significant positive pressurization, the air barrier system can be less than perfect and still achieve the intent of NBC Section 5.4. In buildings that have higher winter humidity levels or are positively pressurized, the air barrier system would have to be closer to perfection to be effective. Benefits gained by mechanical building pressurization should be considered against this continuous loading on the air barrier system. How much leakage is acceptable before problems occur? The NBC does not specify a system air leakage limit because this question is difficult to answer with the current level of knowledge; efforts to define an appropriate number(2) are continuing. The amount of condensation that will occur with a given amount of leakage depends on a number of factors. These include the indoor environment, the outdoor environment, the length and size of the leakage path, and the moisture drainage and drying capabilities. Different construction systems will tolerate different levels of condensation before an undesirable condition arises, and some systems in some locations will permit drying over the summer. Zero leakage is obviously a safe condition to strive for, but realistically it is not likely to be attained.. User’s Guide – NBC 1995 Environmental Separation (Part 5) [99/10/06@11:34]. 5.4. - 3.

(20) Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. Air Leakage. DRAFT COPY. NBC Appendix note A-5.4.1.2.(1) and (2) gives recommended maximum air leakage rates for an air barrier system, depending on indoor relative humidity, for most locations in Canada, and most separator assemblies. Table A-5.4.1.2. of that Appendix note is replicated here as Table 5.4.-1 for the convenience of users. The values provided in the table are for air barrier systems in opaque, insulated portions of the building envelope. They are not for whole buildings, since windows, doors and other openings are not included. The table is provided for guidance when testing air barrier systems as portions of an envelope. Refer to Field Testing at the end of this section. Whole building or system criteria were not required in the NBC for the following reasons: • no library of data on systems performance exists; • the lack of information-sharing in the construction industry would require that each configuration be tested by each firm; • the cost of systems testing to determine compliance would be out of proportion, especially for small or remote projects; • there is no consensus in the industry on an accepted test standard; • there is a lack of knowledge of true maximum systems limits, considering interior and exterior environments, construction materials and assembly details (i.e. case-sensitive criteria); and • whole building tests do not provide information that is useful with respect to providing an effective air barrier system. Guidance is also available from a report published by the Canadian Construction Materials Centre entitled Air Barrier Systems for Walls of Low-Rise Buildings: Performance and Assessment.(3) Table 5.4.-1 Recommended Maximum Air Leakage Rates Warm Side Relative Humidity at 21 C. Recommended Maximum System Air Leakage Rate, L/(s m2) at 75 Pa. < 27%. 0.15. 27 to 55%. 0.10. > 55%. 0.05. To meet the requirements of NBC Section 5.4., the designer must consciously design, and the builder must consciously construct, a barrier to minimize air leakage paths, and this barrier must be effective. 5.4. - 4. over the entire building envelope. A proper design requires more than air impermeable materials to control the passage of air; such materials must also be assembled with essentially leak-free joints. The combination of air impermeable materials with essentially leak-free joints in a ‘constructable’ system (see Section 5.1. of this Guide) provides effective control of air leakage. Refer to Joints and Junctions [5.4.1.2.(7)] in this section.. Air Leakage Limit for Materials and Components in Air Barrier Systems Materials [5.4.1.2.(1)] The primary elements within an air barrier system are the materials that must have low permeance to air flow. These may be materials used in the building envelope for structural or finish purposes, such as cast-in-place concrete, glass or aluminum. However, if the building materials allow large quantities of air to flow through them, as does an unfinished concrete block wall, for example, then impermeable materials must be added to produce low air permeance for the air barrier system. Many materials can provide the airtightness required for an air barrier system. Information on the resistance to air flow of common building materials is available from various sources, including manufacturers’ data sheets. The resistance of 36 building materials is reported in a publication(4) available from Canada Mortgage and Housing Corporation. The air leakage characteristic of 0.02 L/(s m2) at 75 Pa pressure differential required by NBC Section 5.4. is met by 18 of those 36 materials (Table 5.4.-2). The values given in the table are provided on a generic basis; specific materials may have somewhat differing values. This characteristic is provided for materials only, and can not be applied to system air leakage since joints and junctions are not part of the requirement. This characteristic was chosen as a minimum requirement because these materials are: • generally used as air barrier materials (materials that serve as the airtight element of the air barrier system); and • generally accepted as providing adequate airtightness.. [99/10/06@11:34] User’s Guide – NBC 1995 Environmental Separation (Part 5).

(21) Air Leakage. DRAFT COPY. measures to limit air leakage in these exempt assemblies. See Standards [5.3.1.2.(2)] in Section 5.3. of this User’s Guide.. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. Table 5.4.-2 Material Air Leakage Thickness, mm. Material. Air Flow, L/(s m2) at 75 Pa. To ensure continuity between building components, such as doors and windows, and adjoining envelope assemblies, the elements in the assembly and in the component that provide the airtightness function should be clearly understood. For example, drawings should identify the connection between the airtight elements of the air barrier system in the wall and the airtight elements in the component. Some window frame designs facilitate joining between the wall and the window by providing a pre-designed location where the wall air barrier material can be clamped against the window air barrier material. This allows the air barrier system to maintain structural integrity under wind forces, and to resist failure by deterioration or separation of the joint.(5). 0.15. polyethylene. non-measurable. 1.50. roofing membrane. non-measurable. 2.70. modified bituminous membrane torched-on. non-measurable. 0.03. aluminum foil. non-measurable. 1.50. modified bituminous membrane peel and stick. non-measurable. 9.50. plywood. non-measurable. 38.0. extruded polystyrene. non-measurable. 25.4. foil back urethane. non-measurable. Joints and Junctions [5.4.1.2.(7)]. 25.4. phenolic board. non-measurable. 12.7. cement board. non-measurable. 12.7. foil back gypsum. non-measurable. The air barrier system is required to be continuous at joints and junctions. ‘Joints’ is used in this User’s Guide to refer to the joining of two materials and components in the building envelope. ‘Junctions’ refers to the intersection of larger building elements such as walls and roofs; junctions may contain several joints. See Figure 5.4.-3.. 8.0. plywood. 0.0067. 16.0. waferboard. 0.0069. 12.7. exterior gypsum. 0.0091. 11.0. waferboard. 0.0108. 12.7. particle board. 0.0155. reinforced nonperforated polyolefin. 0.0195. Interior gypsum. 0.0196. 12.7. interior finish airtight membrane structure joints window frame. Exceptions [5.4.1.2.(2)] EC01100A. See Exceptions [5.1.4.2.(2)] in Section 5.1. of this User’s Guide.. Figure 5.4.-3 Joints and window/wall junctions showing between airtight materials and components. Components [5.4.1.2.(3) – (6)] Standards are invoked for doors, windows and skylights, in particular the airtightness requirements of CSA A440.1-M, “User Selection Guide to CAN/CSA-A440-M90 Windows.” An exception is provided where a wired glass assembly is installed in an air barrier system as part of a required firerated assembly. This is permitted because there may be a limited selection of such assemblies that meet both the window standards and the fire-resistance standards. Specifications should still require. Joints and junctions are frequently very difficult to detail and construct. The designer should have a clear three-dimensional understanding of how and when each element or component is brought into the assembly, and should then convey that knowledge in as clear a manner as possible by means of largescale detailed drawings and notes. It has proven beneficial in some cases to have details in a form that shows the assembly in three dimensions. Several trades may be involved in the construction of joints and junctions. A pre-construction meeting. User’s Guide – NBC 1995 Environmental Separation (Part 5) [99/10/06@11:34]. 5.4. - 5.

(22) Air Leakage. DRAFT COPY. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. with the trades who will construct the joints or junctions has proven effective in clarifying the methods and sequence to be utilized and reinforcing the importance of the air barrier system. In addition to meeting all requirements of a basic air barrier system, the airtight element at a joint or junction may also have to accommodate movement. The material sealing the joint must be air impermeable and be installed in such a manner that it bridges the gap between, and is compatible with, the air barrier materials on either side of the joint. To maintain the integrity of the air barrier system, the designer and the builder should both have a clear idea as to which element on either side of the joint is performing the principal air barrier function. Joints may be sealed with sealants. Proper design of the joint and proper selection and installation of the sealant is critical to the long-term performance of a joint.(6) Sealants should have the necessary cohesion (internal strength) to remain intact and enough adhesion to remain bonded to the surfaces while undergoing movement. Surface preparation, cleaning and priming to manufacturers’ recommendations, is critical to adhesion. Another method of sealing joints is the use of gaskets. The design of gasketed joints must ensure that the gasket is held in compression under all the conditions the joint may experience. The two materials on each side of the joint should have tolerances within the elasticity of the gasket. If the movement expected may have the potential to “pump” the gasket out of place over time, a means to key the gasketing should be considered. Care should be taken at joints in the gasket, particularly at corners, to ensure continuity of the seal. If a joint is too wide or undergoes too much movement to be bridged effectively by a sealant or gasket, then it must be bridged by an airtight material or component, such as a membrane that is able to absorb the joint movement while remaining tight to all sides of the joint.. Structural Performance [5.4.1.2.(8) – 5.4.1.2.(11)] In building envelope systems, the air barrier system is required to be designed to resist the loads imposed by stack effect, mechanical pressurization and wind. This means that the airtight materials in the air barrier system must themselves be capable of resisting the load, or they must be supported by an element that is. Specific attention must be paid to the materials sealing joints and junctions, since the method of installation, and specifically attachment, of these materials will affect their ability to resist air pressure loads. Since the wind pressure load will 5.4. - 6. ultimately be carried by the structure of the building, the air barrier system must be designed so that the load is transferred to the structure. The largest forces that must be considered in the structural performance of air barrier systems are those from pressure differences induced by wind. These include sustained wind loads and gust wind loads. Specified wind load is the net of the external and internal air pressures on the building assembly. The specified external pressure is the product of the reference velocity pressure for the location [see NBC Sentence 5.2.1.1.(1)] multiplied by an exposure factor, gust factor and external pressure coefficient. The specified internal pressure is the product of the reference velocity pressure for the location [see NBC Sentence 5.2.1.1.(1)] multiplied by an exposure factor, gust factor and internal pressure coefficient. Information on calculating wind loads can be found in the User’s Guide – NBC 1995, Structural Commentaries (Part 4),(7) and in Subsection 4.1.8. of the NBC. Appendix C, Climatic Information for Building Design in Canada, of the NBC, lists hourly design wind pressures for many locations in Canada. The 1-in-10 values are used as the reference velocity pressures for air barrier systems. Deflections caused by winds may create failures of materials and joints. It is required that deflections at 1.5 times the specified load must not adversely affect nonstructural elements of the building assembly. These procedures are especially important when designing air barrier systems for tall buildings. Where an air barrier system is located toward the interior of an assembly, there may be materials on the exterior side that have the properties and capacity to resist some of the wind pressures. Where the air barrier system will not be exposed to full wind load as demonstrated by test or analysis, the air barrier system may be designed and constructed to that lesser load, and deflections of the elements in the air barrier system may be calculated at 1.5 times the lesser load. The structural loads induced by stack effect and fan pressurization will not be the largest loads imposed on the air barrier material by air pressure difference, but they will be endured for longer periods than are wind loads. The air barrier material should be installed in such a manner that it will not detach from its support or fail in creep under these loads. Any benefits derived from mechanical pressurization should be considered against the detrimental effects of this pressure differential potentially introducing indoor air into the wall assembly on a continuous basis.. [99/10/06@11:34] User’s Guide – NBC 1995 Environmental Separation (Part 5).

(23) Air Leakage. DRAFT COPY. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. Durability The air barrier system should perform for the design service life of the assembly in which it is installed. The materials in the system should have a proven track record or otherwise-demonstrated durability (for example, accelerated-aging testing). Failing this, the materials should be positioned so that they are accessible for inspection and maintenance. Durability is not an intrinsic property. It depends largely on how a material reacts to specific environmental factors such as moisture, temperature, solar radiation and adjacent materials. Materials and components are often exposed to several different environments during their service life, one during construction and others after the building has been completed. The environment that the air barrier system is exposed to only briefly during construction may nonetheless be detrimental to the long-term performance of some of the system‘s materials. These materials should always be adequately protected from or be resistant to precipitation, extremes of temperature, solar radiation, wind and mechanical damage during construction. Inadequate protection during storage and construction is a common reason for failure of air barrier materials in practice. See also Section 5.1. of this Guide.. Location The location of the airtight material within the building envelope is governed to a large extent by the same principles that govern the location of the vapour barrier (see Section 5.5., Vapour Diffusion, of the NBC and Guide). In theory, a plane of airtightness anywhere within the building assembly will stop air leakage. In practice, it is generally safer to locate the highest resistance to air flow inside the dew-point plane; that is, on or near the warm side of the insulating materials. This has three advantages: (1) The air barrier system is in a much more stable environment, protected from major temperature and moisture variations. (2) If there are leaks in the air barrier system, the exfiltrating air is more likely to pass to the outside and not be in prolonged contact with materials within the assembly that are below the dew-point temperature of the air, where the probability of condensation would increase. (3) Many materials have low air permeance in combination with low vapour permeance. In other words, most materials that are suitable for controlling air leakage will also perform to some extent as vapour barriers. In this case, the rules governing the location of the vapour barrier will also apply to the airtight material. in the air barrier system. See Section 5.5. of this Guide. Should the air barrier system be located on the cold side of the insulating materials, it is recommended that the water vapour permeance be significantly greater than that of the vapour barrier, or it will become, in effect, the vapour barrier in the wrong location. Refer to High Vapour Resistance on the “Exterior” under Vapour Barrier Properties and Installation [5.5.1.2.] in Section 5.5. of this Guide. Adopting the face-sealed approach to control rain penetration (see Face-Sealed Walls in Sealing and Drainage [5.6.2.1.] of this Guide) requires that the exterior surface of the envelope assembly also serve as the plane of airtightness, with consequent disadvantages. The face-sealed approach can be made to function, but it is unforgiving of minor defects, and therefore requires a high quality of construction and vigilant preventive maintenance.. Testing As part of the recommended quality assurance program (see Durability, Quality Management and Construction, in Resistance to Deterioration [5.1.4.2.] of this Guide), new construction materials and systems should be tested prior to installation in a building. Tests on sections of the building assembly may be made in the laboratory and in-situ. The results are typically repeatable and credible. Whole building tests after completion of construction are expensive and difficult, and the results are generally inconclusive.. Laboratory Testing Except for factory-assembled components, few standards address methods of assessing the air leakage performance of building envelope assemblies. CCMC criteria(3) and ASTM standard E 283-91, “Determining the Rate of Air Leakage Through Exterior Windows, Curtain Walls, and Doors Under Specified Pressure Differences Across the Specimen,” can be used as test procedures for laboratory assessment of the air leakage of building components and assemblies; ASTM standard E 330-97, “Structural Performance of Exterior Windows, Curtain Walls, and Doors by Uniform Static Air Pressure Difference,” can be used as a test procedure for assessment of static structural performance. Both standards describe standard test apparatus and procedures for measuring performance, but they prescribe neither a test pressure difference nor pass/fail criteria. They did form the basis for a series of laboratory evaluations of air barrier systems for wood frame walls,(8) and air. User’s Guide – NBC 1995 Environmental Separation (Part 5) [99/10/06@11:34]. 5.4. - 7.

(24) Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. Air Leakage. DRAFT COPY. barrier membranes for masonry walls.(9) Another standard, AAMA standard 501, “Methods of Test for Metal Curtain Walls,”(10) which uses ASTM standard test procedures, can be used for laboratory assessment of the air leakage control obtained with metal curtain walls. Laboratory tests provide data on the performance of a prototype constructed under conditions that may not be replicated in the field.. Field Testing. References (1). (2). (3). Laboratory procedures can identify the potential performance of an air barrier system. The actual field performance of a given system will depend on the “constructability” of the system and on the workmanship of the trades involved in its installation. Testing full scale mock-ups or pre-built portions of building facades can aid in confirming the achievable performance of the air barrier system or in identifying flaws in its design or constructability. Such tests also provide an excellent opportunity for the constructors to improve their understanding of the design requirements. Testing should be performed at a point in time when repair can be economically achieved (e.g. before insulation and exterior finishes are installed). ASTM standard E 783-93, “Field Measurement of Air Leakage Through Installed Exterior Windows and Doors,” which is the field version of E 283-91, can be used to assess the performance of air barrier systems installed in buildings. This procedure will give an overall assessment of the degree of airtightness achieved with a given installation. Non-standard and non-quantitative techniques involving smoke pencils or smoke generators and infrared and acoustic sensors have been used to locate local leaks in installations of air barrier systems. These qualitative procedures can be used to locate flaws in an otherwise acceptable installation.. (4) (5). (6). (7) (8). (9). (10). An Air Barrier for the Building Envelope– Proceedings of Building Science Insight ’86, National Research Council Canada, Ottawa, 1989. Criteria for the Air Leakage Characteristics of Building Envelopes, report prepared for Canada Mortgage and Housing Corporation by Trow Inc., Ottawa, December 1989. Air Barrier Systems for Walls of Low-Rise Buildings: Performance and Assessment, Canadian Construction Materials Centre, National Research Council Canada, Ottawa, 1997. Air Permeance of Building Materials, report prepared for Canada Mortgage and Housing Corporation by AIR-INS Inc., Ottawa, 1988. Window Performance and New Technology – Proceedings of Building Science Insight ’88, National Research Council Canada, Ottawa, 1988. Ashton, H.E. and Quirouette, R.L., Coatings, Adhesives and Sealants, Performance of Materials in Use – Proceedings of Building Science Insight ’84, National Research Council Canada, Ottawa, 1984. User’s Guide – NBC 1995, Structural Commentaries (Part 4), NRCC 38826, National Research Council Canada, Ottawa, 1996. Testing of Air Barrier Systems for Wood Frame Walls, report prepared for Canada Mortgage and Housing Corporation by W.C. Brown and G.F. Poirier, National Research Council Canada, Ottawa, June 1988. Development of Test Procedures and Methods to Evaluate Air Barrier Membranes for Masonry Walls, report prepared for Canada Mortgage and Housing Corporation by G. Hildebrand, Ortech, Ottawa, November 1990. AAMA standard 501-83, Methods of Test for Metal Curtain Walls, Architectural Aluminum Manufacturers Association, Chicago, 1983.. Supplemental Reading (1) (2) (3). 5.4. - 8. Tek-AID on Air Barrier Systems, Master Specifications and Digest, Construction Specifications Canada, Toronto, 1990. High-Rise Residential Construction Guide, 1995 edition, Ontario New Home Warranty Program, Toronto. 1991 Annual Book of ASTM Standards, Vol. 04.07, Building Seals and Sealants; Fire Standards; Building Constructions, American Society for Testing and Materials, West Conshohocken, Pennsylvania, 1991.. [99/10/06@11:34] User’s Guide – NBC 1995 Environmental Separation (Part 5).

(25) DRAFT COPY. Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays. Section 5.5. Vapour Diffusion Required Vapour Barrier [5.5.1.1.] Section 5.5. of the NBC deals with the control of moisture movement by vapour diffusion. Vapour diffusion is the flow of moisture in vapour phase as induced by vapour pressure difference. Unless exempted, a vapour barrier is required where there is: • a difference in temperature; and • a difference in water vapour pressure. Most of the flow is driven by a difference in vapour pressure, with or without a temperature gradient; a small amount can be driven by temperature gradient alone. Research has shown that it is possible to induce vapour flow even where there is no difference in vapour pressure. For example, air at 15C and 90% RH, and air at 20C and 65.6% RH, both exert a vapour pressure of about 1.53 kPa. The difference in temperature, however, will induce a slow rate of vapour transfer from the warmer air to the cooler. The transfer rate is so slow that it can generally be ignored. Buildings occupied in winter are maintained at temperatures higher than exterior conditions. Even without mechanical humidification systems, the building occupants and their activities will generate moisture that will raise the moisture content of the interior above that of the exterior. Assuming that most building envelope assemblies will be adversely affected by condensation, Section 5.5. of the NBC applies to all buildings identified in the scope of Part 5. Moisture content is not critical except in the context of dew point temperature. If the lower exterior temperature is not below the dew point of the warmer interior air, a vapour barrier is not necessary. This may very likely occur in the case of an internal environmental separator. Some buildings will be maintained at temperatures lower than the exterior conditions. In buildings such as offices that are air-conditioned in the summer, the temperature and vapour pressure gradients are sufficiently shallow and the duration of reversed flow is sufficiently short that designing for vapour diffusion from the exterior to the interior is not an issue in Canada. For other occupancies, such as cold storage plants and freezer buildings, where the interior temperature may be lower than the exterior. temperature for a significant portion of the year, vapour diffusion from the exterior to the interior must be considered.. Exceptions [5.5.1.1.(2)] See Exceptions [5.1.4.2.(2)] in Section 5.1. of this User’s Guide.. Vapour Barrier Properties and Installation [5.5.1.2.] Permeance [5.5.1.2.(1)] Resistance to vapour flow is provided by a vapour barrier, which is a material having a high resistance to vapour transport by diffusion relative to other materials in the assembly. It will limit moisture transport by diffusion through the building assembly from the relatively high vapour pressure found in most building interiors to the relatively low vapour pressure of the exterior air during winter. A vapour barrier will also limit moisture flow between spaces in a building with different vapour pressures. The requirement is not to have a perfectly continuous vapour barrier, but to reduce moisture transfer to a low enough rate to preclude accumulation that could have adverse affects. If an assembly has the ability to drain and vent moisture adequately, then the permeance requirement of the vapour barrier is relaxed (i.e. the barrier may allow more moisture to transfer through at a given vapour pressure differential). Steady state heat transfer and vapour diffusion calculations may be used to select the permeance and location of the vapour barrier. There are also computer simulation programs that allow modelling of dynamic conditions that occur within an assembly under various loads.(1)(2)(3)(4) These can help predict the performance to be expected from an assembly.. User’s Guide – NBC 1995 Environmental Separation (Part 5) [99/10/06@11:34]. 5.5. - 1.