APPLICATION OF ASHRAE/IES 90.1 STANDARD, ONTARIO BUILDING CODE

BRANCH OPINION

RE: Application of ASHRAE/IES 90.1 Standard, Ontario Building Code (OBC), Subsection 2.1.1.

Application of item 9.4.8.3. which is referenced in the ASHRAE/IES 90.1 Standard. Application of such clause to all cases whenever the ductwork within a building envelope carries air with a temperature difference greater than 15 °F of the ambient temperature.

Insulation of supply air ductwork in a concealed ceiling plenum is usually done to ensure the ductwork does not sweat and cause building damage. However, insulating supply air ductwork can also save energy in most cases and reduce air leakage due to improper installation.

According to the interpretation IC 90.1-1989-7 of April 15, 1992, insulation need not be applied on supply air ductwork if heat gains or losses have no negative energy impact such as the following:

exposed supply ducts in the conditioned space they serve,
exposed supply ducts in conditioned spaces other than the space served but which are in the same cooling or heating "mode", or
exposed return ducts in conditioned spaces.

Please be advised that the above ASHRAE/IES 90.1 interpretations is our Branch opinion.

June 03, 1996

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