What are the MURB ventilation requirements for Toronto multi-unit residential buildings?

MURB (Multi-Unit Residential Building) ventilation requirements in Toronto are governed by the Ontario Building Code (OBC), ASHRAE Standard 62.1 for ventilation, and increasingly by the Toronto Green Standard, which imposes additional requirements for new construction and major renovations. Understanding these requirements matters whether you are a condo board member managing building systems, a property manager addressing complaints, or a unit owner trying to understand why your ventilation works the way it does.

The Ontario Building Code (OBC Part 6) sets the baseline ventilation requirements for all MURBs in Toronto. Each dwelling unit must have mechanical ventilation capable of providing a minimum outdoor air supply — typically 0.3 air changes per hour or as calculated per ASHRAE 62.1, whichever is greater. Bathrooms require a minimum 50 CFM exhaust capacity, and kitchens require either a range hood or equivalent exhaust ventilation. All exhaust must terminate outside the building envelope — venting into corridors, ceiling cavities, or common areas is prohibited. The building must also provide corridor pressurization in buildings where corridors serve as the fresh air delivery path to individual suites, maintaining positive pressure in hallways relative to suites so that air flows from the corridor into units through door undercuts.

ASHRAE 62.1 is the engineering standard that most MURB mechanical designers in Toronto reference for detailed ventilation rates. It specifies outdoor air requirements based on both floor area and occupant density — for residential units, the standard requires 0.06 CFM per square foot of floor area plus 5 CFM per person. For a typical 700-square-foot Toronto condo unit assumed to have two occupants, this works out to approximately 52 CFM of outdoor air supply. The standard also addresses exhaust rates, air distribution effectiveness, filtration requirements, and system commissioning — all of which affect how well ventilation actually performs in practice.

The Toronto Green Standard (TGS) adds requirements beyond the OBC for new construction. TGS Tier 1 is mandatory for all new developments requiring site plan approval in Toronto. For MURBs, TGS requires individual suite ventilation systems (rather than relying solely on corridor pressurization), suite-level energy metering, and enhanced air sealing between units. TGS Tier 2 and higher tiers offer development charge refunds in exchange for exceeding minimum requirements, including dedicated outdoor air systems (DOAS), energy recovery ventilation, and enhanced filtration. These requirements are driving a significant shift in how new Toronto MURBs are designed — moving away from the corridor pressurization model toward dedicated in-suite ventilation.

The corridor pressurization model used in most existing Toronto MURBs has well-documented performance problems. Research by the Canada Mortgage and Housing Corporation (CMHC) and University of Toronto has shown that corridor pressurization delivers only 20 to 40 percent of the intended outdoor air to individual suites, with the rest leaking through elevator shafts, stairwells, garbage chutes, and exterior wall penetrations. Stack effect in tall buildings — warm air rising and pulling cold air in at lower floors — overwhelms corridor pressurization during Toronto winters, causing lower-floor units to receive excessive cold drafts and upper-floor units to receive almost no fresh air. This is why many Toronto condo residents on upper floors complain about stuffy air, odours from other units, and condensation on windows despite having a building ventilation system.

For existing Toronto MURBs looking to improve ventilation performance, the most effective upgrades include: compartmentalizing suites with better air sealing between units and corridors (reducing uncontrolled air movement), installing in-suite ERV or HRV units that provide dedicated fresh air to each unit ($2,500 to $5,000 per suite installed), upgrading corridor pressurization fans and controls, and performing regular maintenance on rooftop exhaust fans and makeup air units. These are building-wide projects that require engineering design, condo board approval, and professional installation. Find qualified HVAC and ventilation contractors through the Toronto Construction Network directory.