The new energy efficiency requirements reference effective thermal resistance (or RSI) for the wall assembly as opposed to “nominal” RSI. Effective RSI adds up the thermal resistance associated with all of the components within an assembly. The nominal RSI value for a wall, accounts only for the insulation.
The new energy efficiency requirements reference effective thermal resistance (or RSI) for the wall assembly as opposed to “nominal” RSI. Effective RSI adds up the thermal resistance associated with all of the components within an assembly. The nominal RSI value for a wall, accounts only for the insulation.
(An Effective RSI of 3.08 = R17.5 converts to a Nominal RSI of 3.08 = R13.44)
(Values based on 2×6 framing 16” on center)
BC, Alberta and Manitoba have recently adopted the energy efficiency requirements from the 2010 National Building Code of Canada (Section 9.36). Saskatchewan is also expected to update their requirements shortly.
Builders can use different components to create an assembly that satisfies the total effective RSI prescribed by the local authority having jurisdiction. For both Calgary and Edmonton, the new provisions require above grade walls to have a minimum effective RSI of 3.08 for houses without a heat recovery ventilator (HRV) and 2.97 for houses with an HRV.
The NBC prescribes effective RSI-values for walls, foundations, ceilings, exposed floors and slabs.
The effective RSI better represents the assembly’s resistance to heat loss. It accounts for the heat loss through every component in the assembly including framing. In a wall for example, the thermally conductive wood stud (RSI 1.19) typically increases heat loss. Closely spaced studs increase heat loss even more. Effective R-value takes this all into account. Varying the stud spacing would not have an impact on the nominal RSI value of the wall, which denotes only the nominal RSI value of the insulation. (RSI 3.87 (R22) for the batt).
