78. Despite section 74 and subject to the Regulation respecting the quality of the work environment (chapter S-2.1, r. 11), where the winter indoor design temperature is less than 18 ºC, the minimum thermal resistance R1 shall be determined in conformance with the following formula:
R1 = ti - to • Rt
18 - to
ti = winter indoor design temperature in ºC
to = outdoor design temperature for heating in ºC
Rt = thermal resistance required in section 74 and 75 in m2 • °C/W
This section does not apply to residential occupancy buildings and to hospitals or aid centres.