Defining Scope and Responsibility Under Harmonized OBC Part 9.32:
Exhaust Terminations, Soffit Protection, and the HVAC Designer’s Role
As municipalities begin applying the 2025 harmonization of the National Building Code into Part 9 of the Ontario Building Code (OBC), new questions are emerging around professional scope, permit coordination, and responsibility between design disciplines. One area requiring clarification involves residential exhaust terminations located near vented soffits, and the extent to which HVAC designers should be responsible for identifying, detailing, or mitigating soffit conditions affected by exhaust outlets.
One issue emerging from the 2025 harmonization of the National Building Code into Part 9 of the Ontario Building Code (OBC) concerns residential exhaust terminations and soffit protection requirements.
Recently, a municipality in Eastern Ontario issued permit deficiencies requiring second-floor bathroom exhaust fans and vent terminations to be shown on HVAC design submissions or architectural drawings.
The deficiencies referenced OBC 9.32.3.13.(4) through (6), which require moisture-laden exhaust outlets located within 1.8 metres of vented soffits to be separated from those soffits or mitigated through prescribed soffit blocking or unvented sections.
The code requirement itself is not in dispute. The code reads:
9.32.3.13. Outdoor Intake and Exhaust Openings
(4) Except as provided in Sentences (5) and (5), exhaust outlets that discharge air containing moisture, such as bathroom ventilation and clothes dryer exhaust outlets, shall be located at least 1800mm from air intakes and vented soffits.
(5) Where an exhaust outlet referred to in Sentence (4) is located within a soffit, the soffit shall either be unvented, or if vented, the full depth of the soffit shall be blocked for a distance of 1800mm on each side of the exhaust outlet.
(6) Where an exhaust outlet referred to in Sentence (4) is located in a side wall less than 1800mm from a soffit, a section of the soffit above the exhaust outlet shall be unvented, or if vented, the full depth of the soffit shall be blocked in accordance with the widths stipulated in Table 9.32.3.13.-A, centered over the location of the outlet.
The question is where professional responsibility begins and ends. HVAC designers are responsible for designing mechanical systems, including the sizing, layouts, and termination locations of ventilation systems to meet performance requirements. However, attic ventilation performance and soffit venting design have traditionally fallen outside the scope of HVAC system design and are not reflected within the current BCIN House and Building Services syllabus.
As such, HVAC designers are neither trained nor certified to determine whether modifications to soffit venting could adversely affect attic ventilation performance.
Architectural designers and architects, by comparison, are trained to assess roof assemblies and attic ventilation performance where soffit venting is altered. Consequently, determining the extent of soffit blocking necessary to maintain code-compliant attic ventilation more appropriately aligns with the building envelope discipline.
For the HVAC design industry, HVAC designers should identify any exhaust devices necessary to meet the requirements of 9.32, but in the event that the exhaust device exits through or close to a soffit, specifying how much of the soffits should be blocked and assuming responsibility for attic ventilation calculations falls outside the scope of HVAC design work as currently defined.
Matthew Pedersen, Director
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