9.27.2. Required Protection from Precipitation

9.27.2. Required Protection from Precipitation (See Note A-9.27.2.)
9.27.2.1. Minimizing and Preventing Ingress and Damage
  1. Except where exterior walls are protected from precipitation or where it can be shown that precipitation ingress will not adversely affect occupant health or safety, exterior walls shall be designed and constructed to
    1. minimize the ingress of precipitation into the assembly, and
    2. prevent the ingress of precipitation into interior space. (See Note A-9.27.2.1.(1).)
  2. Except where exterior walls are protected from specific mechanisms of deterioration, such as mechanical impact and ultraviolet radiation, exterior walls shall be designed and constructed to minimize the likelihood of their required performance being reduced to an unacceptable level as a result of those mechanisms.
9.27.2.2. Minimum Protection from Precipitation Ingress
(See Note A-9.27.2.2.)
  1. Except as provided in Sentence (2), a cladding assembly is deemed to have a capillary break between the cladding and the backing assembly, where
    1. there is a drained and vented air space not less than 10 mm deep behind the cladding, over the full height and width of the wall (see also Article 9.27.5.3.),
    2. an open drainage material, not less than 10 mm thick and with a cross-sectional area that is not less than 80% open, is installed between the cladding and the backing, over the full height and width of the wall,
    3. the cladding is loosely fastened to the backing and behind each cladding component there is a clear air space that is
      1. continuous for the full width of the component,
      2. not less than 10 mm deep at the bottom of the component, and
      3. not less than 6 mm deep over not less than 90 mm for every 230 mm of exposed height of the component,
    4. the wall is a masonry cavity wall or the cladding is masonry veneer constructed according to Section 9.20., or
    5. the cladding conforms to Subsection 9.27.13.
  2. The drained and vented air space, and drainage material described in Sentence (1) may be interrupted by
    1. penetrations for windows, doors and services,
    2. flashing, and
    3. furring, provided the furring does not make up more than 20% of the furred area.
  3. Where a construction projects over the top of the drained and vented air space described in Clause (1)(a) or over the drainage material described in Clause (1)(b), the air space or drainage material shall not be contiguous with concealed spaces in the projecting construction.
  4. Exterior walls exposed to precipitation shall be protected against precipitation ingress by an exterior cladding assembly consisting of a first plane of protection and a second plane of protection, where such walls enclose spaces of residential occupancy or spaces that directly serve spaces of residential occupancy.
  5. Except as provided in Sentence (6), exterior walls exposed to precipitation shall be protected against precipitation ingress by an exterior cladding assembly consisting of a first plane of protection and a second plane of protection incorporating a capillary break, where
    1. the number of degree-days is less than 3400 and the moisture index is greater than 0.90, or
    2. the number of degree-days is 3400 or more, and the moisture index is greater than 1.00. (See Sentence 1.1.3.1.(1) and Appendix C for information on the moisture index.)
  6. In exterior walls described in Sentence (5), the first and second planes of protection need not incorporate a capillary break, where
    1. it can be shown that omitting the capillary break will not adversely affect the performance of the building assemblies,
    2. the building is an accessory building, or
    3. the wall
      1. is constructed of non-moisture-sensitive materials, and intersecting or supported floors are also constructed of non-moisture-sensitive materials, or
      2. is constructed as a mass wall of sufficient thickness to minimize the transfer of moisture to the interior.
9.27.2.3. First and Second Planes of Protection
  1. Where walls required to provide protection from precipitation comprise cladding assemblies with first and second planes of protection,
    1. the first plane of protection shall
      1. consist of cladding with appropriate trim, accessory pieces and fasteners, and
      2. be designed and constructed to minimize the passage of rain and snow into the wall by minimizing holes and managing precipitation ingress caused by the kinetic energy of raindrops, surface tension, capillarity, gravity, and air pressure differences (see Subsection 9.27.4.),
    2. the second plane of protection shall be designed and constructed to (see Subsection 9.27.3.)
      1. intercept all rain and snow that gets past the first plane of protection, and
      2. effectively dissipate any rain or snow to the exterior, and
    3. the protection provided by the first and second planes of protection shall be maintained
      1. at wall penetrations created by the installation of components and services such as windows, doors, ventilation ducts, piping, wiring and electrical outlets, and
      2. at the interface with other wall assemblies.
9.27.2.4. Protection of Cladding from Moisture
  1. A clearance of not less than 200 mm shall be provided between finished ground and cladding that is adversely affected by moisture, such as untreated wood, plywood, OSB, waferboard and hardboard.
  2. A clearance of not less than 50 mm shall be provided between a roof surface and cladding that is adversely affected by moisture, such as untreated wood, plywood, OSB, waferboard and hardboard.

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