Maintenance and Repairs

August 4, 2026 Published by Toronto and Area Chapter - By Sophia Rojenko

A Tight Seal, A Bigger Problem

From the Summer 2026 issue of CCI Toronto Condovoice Magazine.

Noise, cold drafts, and odours are common complaints in high-rise condos. To the average resident, there may appear to be a simple fix – weatherstrip your suite corridor door. But what many residents don’t realize is that this seemingly small modification can lead to a much bigger problem than the ones they were trying to solve.

For many buildings, particularly those from the early 2000s or earlier, the mechanical systems are designed so that the suites are ventilated through corridor pressurization. In these buildings, the units do not have dedicated in-suite ventilation such as Energy Recovery Ventilators (ERVs) or Heat Recovery Ventilators (HRVs). Instead, a central makeup air unit (or multiple units) brings in fresh outside air and pressurizes the corridors. This air may also be tempered by heating and cooling. The gaps around the suite doors allow this air to flow from the corridor into the units, providing ventilation. When suite doors are weatherstripped, these gaps are sealed, effectively cutting off the primary source of fresh air to the unit.

A common complaint in cold-weather climates like ours during the winter is condensation on windows. While condensation can result from a variety of factors, it is often a symptom of occupant behaviour. Condensation can be the result of generating high interior humidity from running a humidifier or keeping many houseplants. Similarly, failing to expel humid air can be just as problematic - for example, failing to run exhaust fans when showering or cooking. Condensation is also a common (albeit annoying) symptom of single-pane windows where interior glass surfaces are colder and therefore more susceptible to condensation forming.

When reports of condensation are received, management should first verify whether the residents have installed weatherstripping on their suite door, as this can be a significant contributing factor. By sealing the gaps around the suite door, weatherstripping restricts airflow from the corridors into the unit. This causes indoor humidity levels to rise, which in turn results in condensation. Additionally, during cold weather, most residents are unlikely to open windows, meaning that there is effectively no alternative source of ventilation provided to the unit. Without adequate ventilation, indoor air quality rapidly deteriorates.

Another concern with weatherstripping suite doors is that it has an impact on exhaust fan operation. When the kitchen or washroom exhaust fans are activated, replacement air must be drawn from somewhere to balance the pressure. With the suite door sealed, the unit cannot pull air from the corridor. Instead, air is pulled through any unsealed penetrations, such as plumbing stacks, electrical outlets, or other concealed pathways. This can introduce unwanted odours from neighbouring suites or other parts of the building.

Another concern with weatherstripping suite doors is that the air intended to enter the suites is forced to divert elsewhere, such as into elevator shafts and stairwells, or may even backflow into other suites whose doors aren’t weatherstripped. For example, if 100 CFM of supply air was intended to be delivered to each suite, but 60% of the suites have weatherstripped their doors, that airflow needs to be redistributed to the building. This can unintentionally lead to excessive pressurization, can cause difficulty opening suite doors and can even impact the operation of elevator doors. In some cases, if the pressurization is excessive, it can result in doors forcefully pushing or pulling when opened.

Weatherstripping suite doors is appropriate when suites are equipped with dedicated ventilation systems, such as ERVs or HRVs. In these buildings, suite ventilation is provided directly from within the unit, while the makeup air system is intended solely for corridor and common area pressurization. Because suite ventilation is compartmentalized under this design, sealing the suite doors does not impede the delivery of fresh air. In fact, properly installed weatherstripping can help maintain the pressure separation and support the overall air balance within the building.

If your building relies on corridor pressurization to ventilate the suites, it is important that residents be educated not to install weatherstripping on their corridor doors, as this can interfere with the intended ventilation and air balance. If you are unsure of the ventilation system your building has, the corporation’s engineer can assist.

Sophia Rojenko, P. Eng., Synergy Partners