54. The thermal resistance of a building assembly may be reduced by not more than 20% form that required in sections 51 and 52, on the condition that the thermal resistance of other assemblies of the building are increased, so that the total calculated heat loss from the building enclosure does not exceed the heat loss that would result if the enclosure were in conformity with sections 51 and 52.
For the purpose of this section, the calculated heat loss must not take into account the solar heat gain.