Skylights and Light Wells in Cottages

Why Overhead Light Is Different

Horizontal or near-horizontal glazing intercepts sunlight across a much larger portion of the day than a vertical window of equivalent area. The sky hemisphere above a flat roof is always partly visible; a south-facing vertical window only receives direct sun during a limited arc. This makes overhead glazing disproportionately effective at delivering light volume — though it also introduces more total solar heat gain and, in Canadian winters, greater heat loss if the skylight is not well-insulated.

Fixed Skylights

A fixed skylight is a glazed unit set into the roof structure. It does not open. Fixed skylights are simpler than venting units — fewer moving parts, lower maintenance, and generally better long-term air-sealing performance. They are appropriate for spaces where ventilation is provided by other means (operable windows elsewhere in the space, a mechanical ventilation system).

In cottages on sloped roofs, skylights are installed parallel to the roof slope (on-slope installation) or in curb-mounted configurations that raise the glazing slightly above the roofline. Curb-mounted units are generally easier to flash and seal correctly on a renovation project; on-slope (deck-mounted) units sit lower and can look more integrated but require precise flashing installation to prevent water ingress.

Venting Skylights

Venting skylights include a mechanism — manual crank, electric motor, or remote-operated actuator — that opens the unit for airflow. They serve a dual purpose: daylighting and natural ventilation. In a cottage without air conditioning, a venting skylight positioned at or near the ceiling can exhaust warm air rising from the space (stack effect ventilation) while admitting cool replacement air through lower openings.

The trade-off against fixed units is mechanical complexity and higher cost. Electric actuators can fail; the associated wiring adds cost. In cottages that are unheated in winter, freeze-thaw cycles on mechanical components require periodic maintenance. Manual venting skylights eliminate some of this complexity but are impractical in high ceiling applications.

Tubular Daylight Devices (Solar Tubes)

A tubular daylight device consists of a small dome on the roof (typically 250–350 mm diameter), a highly reflective flexible tube passing through the ceiling cavity, and a diffuser lens at the ceiling level. The reflective interior surface bounces light down the tube and distributes it into the room below.

These units are particularly suited to spaces where a full skylight is not structurally practical — such as above a bathroom in a cottage with a finished attic above — and to dark interior rooms where no direct roof access is convenient. Their output is entirely diffuse; they do not admit a beam of direct sunlight, which some people prefer.

Performance in Canadian Winter

Solar tubes function in winter, though output is reduced. Snow accumulation on the dome temporarily reduces light transmission; most dome profiles are convex and self-clearing under moderate snowfall. In regions with sustained heavy snowfall, the dome may be covered for extended periods. Some manufacturers offer heated dome options, but these add cost and require wiring.

Light Wells

A light well is an interior shaft that connects a roof opening or upper-floor window to a lower level. In a two-storey cottage, a light well can be cut through the upper floor to deliver overhead daylight to the ground floor without a full roof structure opening. The shaft is lined with highly reflective surfaces — typically matte white paint — to maximize the amount of light that reaches the bottom.

The efficiency of a light well decreases with depth and depends heavily on the reflectance of the shaft walls. A rough calculation: each reflection inside the shaft loses some percentage of the incoming light depending on surface reflectance. A shaft lined with high-reflectance matte white (reflectance around 0.85) retains useful light levels at depths of 1.5–2 m. Beyond that, output becomes marginal for most tasks, and a tubular daylight device with its highly polished internal surface is more effective.

Installation Considerations for Canadian Climates

• Thermal performance: Any roof penetration introduces a potential thermal bridge and condensation risk. Skylights should have a centre-of-glass U-factor appropriate for the climate zone. In most Canadian cottage regions (climate zones 5–7 under the National Building Code), a U-factor no higher than 2.0 W/m²K (approximately U-0.35 in imperial units) is a reasonable minimum for a fixed skylight.
• Flashing: Improper flashing is the primary cause of skylight failure. The roofing contractor's experience with skylight installation in local conditions — particularly ice dam management — matters as much as the quality of the unit itself.
• Condensation on interior glass: In humid interior spaces (bathrooms, kitchens), the inner glass surface of a skylight can condense moisture in cold weather even with double or triple glazing. A condensation channel at the frame perimeter is a standard feature on quality units; confirm its presence on any unit being installed in a high-humidity location.
• Glazing for solar control: In cottage applications without mechanical cooling, a high solar heat gain coefficient (SHGC) on a skylight can cause overheating in summer. A roof-mounted shade or external blind, or a low-SHGC glazing specification, may be appropriate depending on the building's thermal mass and natural ventilation capacity.

Last reviewed: May 2026. References: National Research Council Canada, Natural Resources Canada building energy guidance.