Should I install a window in my interior Vancouver bathroom or rely on ventilation only?

For an interior Vancouver bathroom with no exterior wall, rely on a high-quality mechanical ventilation system rather than trying to add a window — it will manage moisture far more effectively than a window ever could in Metro Vancouver's humid climate, and it avoids the significant structural cost of routing a window to an exterior wall. Even bathrooms that already have windows should not rely on them as the primary moisture management strategy in this region.

This is a question where Vancouver's climate makes the answer different from what you might hear in drier parts of Canada. In Calgary or Winnipeg, where outdoor humidity regularly drops below 30%, opening a bathroom window after a shower allows dry outside air to quickly absorb and carry away moisture. In Metro Vancouver, where outdoor humidity averages 75–85% year-round and exceeds 90% on many fall and winter days, opening a window brings in air that is already saturated with moisture. That air cannot absorb the humidity from your shower — it just circulates damp air through the room without drying anything. On a typical November day in Vancouver with 90% outdoor humidity and drizzle, an open window actually makes your bathroom moisture problem worse.

Mechanical ventilation is the only reliable moisture management strategy for Vancouver bathrooms. Install an exhaust fan rated at a minimum of 80 CFM for a standard bathroom, or 110 CFM for a larger bathroom or one with a soaker tub that generates more steam. The fan must be ducted to the exterior of the building — through the roof or an exterior wall — and never into an attic, soffit, or wall cavity. Exhausting into the attic is a BC Building Code violation and causes condensation, mould growth, and wood rot in the attic structure.

The best fan setup for an interior Vancouver bathroom includes a humidity-sensing switch ($80–$150 for the switch; $200–$400 for installation) that automatically turns the fan on when humidity rises above a set threshold (typically 60%) and runs it until the moisture clears. This is vastly superior to relying on the homeowner to remember to turn the fan on and leave it running — most people turn the fan off when they leave the bathroom, but the moisture needs another 15–20 minutes of ventilation to clear properly. A timer switch ($40–$80 installed) is a more affordable alternative that runs the fan for a preset period after you leave. Total cost for a quality exhaust fan installation in an interior bathroom: $400–$900 including fan, ducting, switch, and electrician.

If your home has an HRV (Heat Recovery Ventilator) system, connecting the bathroom exhaust to the HRV is the gold standard for ventilation in Metro Vancouver. The HRV recovers heat from the outgoing moist air and transfers it to the incoming fresh air, improving energy efficiency while providing continuous controlled ventilation. Many newer homes and condos in Metro Vancouver are equipped with HRV systems, and integrating bathroom ventilation into the HRV is increasingly standard practice.

The structural cost of adding a window to an interior bathroom is prohibitive. An interior bathroom, by definition, does not share a wall with the building exterior. Adding a window would require either routing a light shaft or window tunnel through adjacent rooms, closets, or the ceiling to reach an exterior wall or roof — a major structural modification costing $5,000–$15,000 or more. In a condo or strata building, cutting an opening in an exterior wall is almost never permitted, as exterior walls are common property controlled by the strata corporation.

Alternatives that bring light without a window: A tubular skylight or sun tunnel ($1,000–$3,000 installed) captures natural light from the roof and channels it through a reflective tube into the bathroom ceiling. This works well in single-storey homes or top-floor bathrooms. Frosted glass interior transoms or sidelights ($300–$800 installed) above the bathroom door or in an adjacent wall borrow light from hallways or rooms with windows. An LED light panel that mimics natural daylight ($200–$500) can simulate the psychological benefits of a window.

Bottom line: Invest in excellent mechanical ventilation — a quality exhaust fan with a humidity-sensing switch, properly ducted to the exterior. This is the single most important installation in any interior Vancouver bathroom and will do more to prevent mould than any window could in this climate. Budget $400–$900 for the complete ventilation installation and consider it a non-negotiable part of any bathroom renovation.