1.0
1.1 It is the intent of this Specification section to provide an overview of the principles of building science,
and a general understanding of the exterior and interior building enclosures principles.
1.2 No recommendation or statement in the documents listed in Article 3 herein is a mandatory
requirement of the Contract unless specified in the Specification section or detailed on the Drawings in the Contract Documents for this Project.
1.3 Review the Drawings and the Specifications to understand these principles and the necessity for
certain procedures, sequence and coordination of construction. BUILDING SCIENCE
2.0
2.1 Drawings and Specification sections for the Work which forms the construction of the exterior building
enclosure and differing environmental interior separations are based on the principles of building science developed from research and studies by the National Research Council of Canada (NRCC), National Research Council’s Institute for Research in Construction (I.R.C.) formerly called the Division of Building Research.
2.2 Building envelope design requirements shall include, but not be limited to the following:
2.2.1 Comply with the applicable Building Code, and other regulations and requirements of the
authorities having jurisdiction, for the design, engineering, fabrication and installation of the Work.
2.2.2 Accommodate the tolerance limitations of the structure, and the creep, deflection and other
movements of the structure.
2.2.3 Design the building envelope assemblies to provide for expansion and contraction of
components as will be caused by the ambient temperature range and surface temperature variation of components, and structural movements, without causing distortion, failure of joint and air/vapour barrier seals, and/or causing undue stress or other defects detrimental to the appearance or performance of the building envelope assemblies.
2.2.4 Design the building envelope assemblies to withstand within acceptable deflection limitations,
their own weight, forces applied by the movements of the building structure and attached adjacent components, and the maximum design loads due to snow, ice, rain, hail, seismic, and the positive, negative and peak gust pressure of the wind.
2.2.5 The Work shall accommodate, by means of expansion and contraction provisions, any
movements in the building envelope assemblies themselves and between the assemblies and the building structure, caused by structural movements, both deflection and racking, and/or thermal expansion and contraction, without distortion, damage, misalignment of joints, breakage of air/vapour barriers, water and air penetration through the assembly, or glass breakage.
2.2.6 Reinforce the building envelope assembly components as required so that the members can
safely sustain the design loads.
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2.2.8 Design light gauge, aluminum structural members in accordance with CSA-S157-M83
(R2000).
2.2.9 Design, assemble and secure the building envelope assemblies in a manner which will keep
stresses on the sealants within the maximum recommended by the sealant manufacturer. 2.2.10 In designing the structural framework of the building, the Consultant has made assumptions
as to the magnitude, direction and points of application of the loads imposed on the structure by the building envelope assemblies.
2.2.11 The building envelope shall have a method of attachment to the structure which shall take into account the site peculiarities so that there shall be no possibility of site and air vibrations or normal temperature movements of the building which could loosen, weaken and/or fracture the connection between building envelope assembly components and the structure, or between the components themselves.
2.2.12 To conform to these principles, a continuous, unbroken or non-perforated structurally supported air seal totally enclosing the building envelope and separating the interior and exterior environments is required. This includes the exterior wall systems, the roof systems, the junctions of walls and roofs and installation of carefully located sealants at frames of openings and seals at doors and windows.
2.2.13 Air seal materials may be Products which shall include but shall not be limited to;
membranes, sealants, metal, and glass as specified in the Specifications and/or shown on the Drawings.
2.2.14 Special care is required to join and seal the junction of different types of air seal Products to maintain air seal continuity. Compatibility of adhesives and sealants with one another and with the surfaces to which they are applied is essential.
2.2.15 Gaskets (weather-seals) to minimize air leakage are used at openings such as doors, roof hatches and windows. Sealant is used to provide continuity of air seal at framed openings.
2.3 Water, vapour and moisture protection design requirements shall include, but not be limited to the
following:
2.3.1 Comply with the design and performance requirements specified in the applicable Building
Code and as specified herein, and design and engineer the Work accordingly. In designing and engineering the Work, the principles shall include but not be limited to:
2.3.1.1 Make provisions to drain to the exterior face of the assembly, any water entering at
joints and any condensation occurring within the building envelope assembly.
2.3.1.2 Design, fabricate and install the assembly to be watertight to the interior under the
interior and exterior design conditions in combination with movements occurring due to loads imposed.
2.3.1.3 At design conditions, no water penetration to the building interior side of the
assembly shall occur.
2.3.1.4 The requirements for an air barrier and a vapour barrier are intended to be provided
at the same plane in the building envelope design unless indicated or specified otherwise. In such cases, the Drawings and Specifications refer to "air/vapour barrier". The definition of the air/vapour barrier for the purpose of these
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Specifications is "a continuous membrane including joins of membrane between components and to adjacent construction which prevents or retards penetration of moisture laden air and the diffusion of water vapour through it".
2.3.1.5 The maximum air leakage of all components forming the air barrier shall be 0.030
cfm/min/ft2 (0.150 L/sec/m²) measured at an air pressure difference of 1.57 lb/ft2 (75 Pa), unless specified otherwise.
2.3.1.6 The maximum water vapour transmission of all components forming the vapour
barrier shall be 0.261 grains/h/ft²/in/Hg (15 Ng/Pa/sec/m²), Type 1 vapour barrier, unless specified otherwise.
2.3.1.7 At exterior wall conditions, no condensation shall occur on room side surfaces.
2.4 Rain screen principle design requirements shall include, but not be limited to the following:
2.4.1 Base the design of building envelope assemblies on the "Rain Screen" principle.
2.4.2 The definition of the rain screen principle for the purpose of the Specifications is as
advocated by the “National Research Council of Canada". All voids between the assembly components as well as those between components and the structure shall have the following:
2.4.2.1 Gaskets, baffles, overlaps, seals and compartmentalization as required providing a
"rain screen" barrier to effectively prevent excessive rain water entry into any of the building’s envelope cavities, but which allow pressure equalization of cavity air spaces.
2.4.2.2 Use low permeability vapour barriers to minimize vapour diffusion.
2.4.2.3 Provide air barriers and seals as required to prevent the entry of interior building air
into building envelope cavities, and exterior air into the building(s). Air barriers and seals shall be able to withstand wind design pressures.
2.4.2.4 Such provisions in the form of openings between cavities and the building exterior
of sufficient cross sections to provide adequate pressure equalization. All openings shall be effectively baffled against direct rain water entry. Air spaces shall be baffled and compartmentalized to prevent chimney effect within the air spaces for each storey vertically and also horizontally.
2.4.2.5 Thermal separators, isolators and seals shall be placed to eliminate contact
between interior humid air and a cold surface or structural component to prevent condensation and ice build-up on such surfaces during cold weather.
2.4.3 Exterior rain screen is designed to allow for ventilation, drainage, and air pressure
equalization of the air space between the rain screen and the insulation with the outside air pressure. Different air pressures occur at various locations on the exterior surfaces due to wind forces. Air spaces are divided into separate compartments as a means of controlling these differences.
2.4.4 Continuous thermal insulation shall be applied tight to the exterior side of the air seal to
eliminate air pockets and channels. Construction details may indicate some exceptions where fastenings are required through the insulation or where structural elements occur.
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Thermal bridges thus created, shall be constructed to minimize heat losses or condensation problems.
2.5 Wind load design requirements shall be as follows:
2.5.1 Provide uniform wind load design based on the more stringent of the maximum wind loading
pressures for positive, negative and peak wind gusting of the applicable Building Code, with a return period probability of one (1) year of any thirty (30) years.
2.5.2 In addition to the foregoing, attention shall be given to areas of the building(s) subject to
increased pressures at the eaves, canopies and external corners where the geometry of the building(s) and relationships with other buildings may cause increased wind loads due to wind vortex and wind eddy conditions, which in turn may cause increased ice, rain, snow and snow build-up loads.
2.6 Seismic load design requirements shall include, but not be limited to the following:
2.6.1 Design wall and roof assemblies to prevent damage due to earthquake forces as required by
the applicable Building Code requirements.
2.7 Air infiltration and exfiltration design requirements shall include, but not limited to the following:
2.7.1 Air infiltration and exfiltration through the completed cladding systems shall not exceed 0.02
cfm/sq.ft at 2" static pressure difference (0.1 litre/sec/sq.m at 500 Pa static pressure difference).
2.8 In some instances the above building science principles may apply to internal walls where
temperature and humidity conditions differ between two zones. (eg. a hockey rink and a swimming pool).
REFERENCES