What's the best way to add a window or more natural light to an interior bathroom?

Adding natural light to an interior bathroom — one with no exterior wall — requires creative solutions like tubular skylights, borrowed light from adjacent rooms, glass block, or frosted glass transoms, since adding a conventional window is only possible when the bathroom shares an exterior wall. Interior bathrooms are extremely common across the GTA, especially in condos, post-war bungalows with central bathrooms, and multi-bathroom homes where the second or third bathroom is landlocked in the floor plan.

If your bathroom does share an exterior wall, adding or enlarging a window is the most impactful natural light upgrade. In Toronto, this requires a building permit from the City of Toronto Building Division because you are modifying the building envelope, and potentially a structural header above the new window opening if you are cutting into a load-bearing wall. A standard bathroom window installation (vinyl, frosted or obscure glass for privacy) costs $1,500–$4,000 in the GTA including the window, framing, exterior finishing, and interior trim. Use tempered, obscure glass — privacy glass that lets light in without transparency. Frosted or rain-pattern glass is the most popular choice for GTA bathroom windows.

Tubular Skylights (Sun Tunnels)

For interior bathrooms in houses (not condos), a tubular skylight (also called a sun tunnel or light tube) is the most effective solution. Brands like Velux Sun Tunnel and Solatube capture daylight on the roof through a small dome (10–14 inches in diameter), channel it through a highly reflective tube through the attic space, and deliver it into the bathroom through a ceiling diffuser. The result is surprisingly bright natural light in a room that has no exterior walls. Installation costs $800–$2,000 in the GTA depending on roof accessibility, tube length, and whether any attic obstructions need to be navigated. The roof penetration is small and properly flashed — far less invasive than a traditional skylight.

Traditional flat or curb-mounted skylights are also an option if your bathroom is directly below the roofline, but they are more expensive ($2,000–$5,000 installed), more prone to leaking if not installed by an experienced roofer, and can create unwanted heat gain during Toronto's hot summers. If you go this route, choose a vented skylight that can open to release bathroom moisture — this provides both natural light and supplemental ventilation.

Borrowed Light Strategies

Interior windows and transoms between the bathroom and an adjacent room are an increasingly popular solution in GTA renovations. A frosted or reeded glass transom window above the bathroom door allows light from the hallway to enter the bathroom while maintaining privacy. A fixed interior window (frosted or obscure glass) between the bathroom and an adjacent bedroom or hallway does the same. These cost $400–$1,200 installed depending on size and glass type. If the wall between the bathroom and the adjacent room is load-bearing, you will need a properly sized header — a structural consideration that requires professional assessment.

Glass block panels were once the standard solution for borrowed light in GTA bathrooms. While they have fallen out of fashion aesthetically, modern alternatives like fluted glass, reeded glass, and frosted glass panels in slim metal frames achieve the same light-borrowing function with a much more contemporary look.

Maximizing the Light You Have

Even without adding new light sources, you can dramatically improve how bright an interior bathroom feels. Large mirrors — ideally wall-to-wall above the vanity — reflect and multiply whatever light exists. Light-coloured tile and paint (whites, light greys, soft creams) on walls, floor, and ceiling bounce light around the room rather than absorbing it. Glass shower enclosures instead of opaque shower curtains allow light to flow through the entire space. High-quality LED lighting at 3000K–4000K in sufficient quantity can closely simulate the feel of natural daylight.

For condo bathrooms, your options are limited to borrowed light strategies and optimized artificial lighting — you cannot add skylights or exterior windows in a high-rise. A frosted glass panel or transom between the bathroom and the master bedroom is the most practical condo solution, and most condo corporations will approve this since it does not affect common elements or the building envelope.