Ministry of Municipal Affairs
PROPOSED CHANGE TO THE 2012 BUILDING CODE
O. REG. 332/12 AS AMENDED
CHANGE NUMBER:
B-9-25-05
SOURCE:
Ontario
CODE REFERENCE:
Division B / 9.25.4.2.
DESCRIPTION OF THE PROPOSED AMENDMENT
The proposed change permits the use of semi-permeable and variable permeance vapour retarders in basement
wall assemblies.
EXISTING 2012 BUILDING CODE PROVISION(S)
9.25.4.2. Vapour Barrier Materials
(1) Vapour barriers shall have a permeance not greater than 60 ng/(Pa∙s∙m2), measured in accordance with
ASTM E96 / E96M, “Water Vapor Transmission of Materials”, using the desiccant method (dry cup).
(2) Where the intended use of the interior space will result in high moisture generation, the assembly shall be designed
according to Part 5. (See Appendix A.)
(3) Where polyethylene is installed to serve as the vapour barrier, it shall conform to CAN/CGSB-51.34-M, “Vapour
Barrier, Polyethylene Sheet for Use in Building Construction”.
(4) Membrane-type vapour barriers other than polyethylene shall conform to CAN/CGSB-51.33-M, “Vapour Barrier,
Sheet, Excluding Polyethylene, for Use in Building Construction”.
(5) Where a coating is applied to gypsum board to function as the vapour barrier, the permeance of the coating shall be
determined in accordance with CAN/CGSB-1.501-M, “Method for Permeance of Coated Wallboard”.
(6) Where insulation functions as the vapour barrier, it shall be sufficiently thick so as to meet the requirement of
Sentence (1).
PROPOSED CODE CHANGE
9.25.4.2. Vapour Barrier Materials
(1) Except as provided in Sentences (2), Vapour barriers shall have a permeance not greater than 60 ng/(Pa∙s∙m2),
measured in accordance with ASTM E96 / E96M, “Water Vapor Transmission of Materials”, using the desiccant method
(dry cup).
Building and Development Branch
© Copyright Queen’s Printer for Ontario 2016
Page 1
(2) Thermally insulated basement wall assemblies are permitted to be constructed with vapour retarders in lieu of a
vapor barrier required in Sentence (1) provided that vapour retarder have permeance not greater than 300 ng/(Pa•s•m2),
measured in accordance with ASTM E96, “Water Vapor Transmission of Materials”, using the desiccant method (dry
cup).
(23) Where the intended use of the interior space will result in high moisture generation, the assembly shall be designed
according to Part 5. (See Appendix A.)
(3 4) Where polyethylene is installed to serve as the vapour barrier, it shall conform to CAN/CGSB-51.34-M, “Vapour
Barrier, Polyethylene Sheet for Use in Building Construction”.
(45) Membrane-type vapour barriers other than polyethylene shall conform to CAN/CGSB-51.33-M, “Vapour Barrier,
Sheet, Excluding Polyethylene, for Use in Building Construction”.
(56) Where a coating is applied to gypsum board to function as the vapour barrier, the permeance of the coating shall be
determined in accordance with CAN/CGSB-1.501-M, “Method for Permeance of Coated Wallboard”.
(67) Where insulation functions as the vapour barrier, it shall be sufficiently thick so as to meet the requirement of
Sentence (1).
RATIONALE FOR CHANGE
Problem/General Background
The use of low-permeance polyethylene as a combined air and vapour barrier is well-integrated in other building
codes and is practiced widely in the Canadian construction industry. The purpose of this vapour barrier is to
prevent vapour-diffusion through the materials from contacting the cold upper portion of the wall in winter.
However, there are concerns that the current approach may affect interior drying and exacerbate summer
condensation. In this case, there is a risk for moisture-sensitive assemblies, since the concrete wall can collect
sources of water, either from construction moisture, liquid or capillary flow, or vapor diffusion from the
surrounding soil. In warmer Canadian climates, such as southern Ontario, walls may experience vapour flow to
the interior, especially in air-conditioned homes. According to CMHC’s research, an interior impermeable layer
at the lower portion of the basement wall reduces drying and results in longer periods of elevated humidity at the
concrete-insulation interface. In some cases, the flow of water vapour inward is so powerful that a low permeance
barrier on the inside can result in condensation on the exterior face of this barrier. This condensate may affect
indoor air quality and framing.
Justification/Explanation
Permitting the installation of semi-permeable materials or variable permeance materials in basement wall
assemblies allows for inward drying during the summer. This lowers the risk of excessive moisture accumulation,
the potential for mould growth and the decay of framing, if high moisture content exists in the assembly. Research
suggests that variable permeance materials allow for inward vapor diffusion, due to their ability to increase
permeability at elevated relative humidity levels. The use of variable permeance materials can also help maintain
the assembly’s relative humidity levels below the 75% mould growth threshold.
Cost/Benefit Implications
Material costs will vary depending on the selection of semi-permeable materials or variable- permeance materials,
and whether the material is installed over the full area or a portion of the basement wall. Benefits include an
enhancement to indoor air conditions and a reduction in homeowner complaints related to sustained moisture
conditions in the basement.
Building and Development Branch
© Copyright Queen’s Printer for Ontario 2016
Page 2
Enforcement Implications
None anticipated.
Who is Affected
Building Official, Designers, and Builders.
Objective Based Analysis
None.
OTHER SUPPORTING MATERIALS
Building and Development Branch
© Copyright Queen’s Printer for Ontario 2016
Page 3