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Adding a flat roof skylight is one of the best ways to brighten up an interior space and increase property value. Whether you’re installing a new skylight or replacing an old unit, it’s important to understand the unique requirements for flat roof applications—especially in Toronto’s climate.
In this guide, we’ll cover everything you need to know about choosing, installing, and maintaining a flat roof skylight, as well as avoiding common mistakes that lead to leaks or energy loss.
Why Install a Flat Roof Skylight?
A flat roof skylight brings in natural light, reduces electricity use, and can dramatically improve how a space feels. In homes, they’re perfect for kitchens, bathrooms, or converted lofts. In commercial buildings, they reduce lighting costs and create a more inviting atmosphere for employees and customers.
Toronto’s urban architecture often includes flat roofing on bungalows, extensions, and low-rise buildings, making skylights a practical way to upgrade without changing the entire roofline.
Types of Skylights for Flat Roofs
Unlike sloped roof skylights, flat roof skylights must be carefully designed to avoid water pooling. The most common options include:
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Curb-mounted skylights: Raised slightly above the flat roof surface for better drainage
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Domed or pyramid skylights: Made with acrylic or polycarbonate, these designs naturally shed water
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Opening skylights or roof windows: Ideal for ventilation as well as light
When choosing a skylight on a flat roof, always opt for models that are energy-efficient and designed for low-slope applications. Brands like VELUX Canada offer excellent skylight systems tailored to flat roofs with multi-layer sealing systems and UV protection.
Considerations Before Installing
Installing a flat roof skylight is not the same as cutting into a sloped asphalt roof. Flat roofs require waterproofing layers, and any penetration can compromise those if not properly sealed.
Here’s what to consider:
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Roof age and material: Don’t install a skylight on a deteriorated or worn-out flat roof. It’s best to combine it with a full roof upgrade if needed.
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Drainage planning: The skylight must be installed at a high point or paired with tapered insulation to prevent pooling.
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Permits and building codes: Toronto requires permits for most structural changes—check with your contractor or city office.
Replacing an Old Flat Roof Skylight
Over time, older skylights can become cloudy, drafty, or leak around the frame. Replacing a flat roof skylight is a smart move if your current one is more than 15–20 years old.
Warning signs include:
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Condensation between glass panes
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Water stains around the skylight frame
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Cracked dome or glazing
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Difficulty opening or closing roof windows
During replacement, it’s also common to find roof membrane issues or flashing failures, which should be repaired simultaneously. A professional inspection from Flat Roof Toronto can help determine whether it’s time for a full replacement or just resealing.
Skylight Flashing & Waterproofing
One of the most critical parts of any flat roof skylight installation is the flashing. This is where many DIY installations fail. Poorly sealed flashing or incorrect placement of waterproof membranes is a recipe for long-term leaks.
Use high-performance flashing kits that are compatible with your roof system. Columbia Skylights offers several flat roof-specific kits that are CSA-approved and highly weather-resistant.
Energy Efficiency & Roof Windows
Many newer roof window Toronto products come with double or triple glazing, argon-filled chambers, and low-E coatings to reduce heat loss. If you’re replacing a skylight, choose models with ENERGY STAR® ratings to reduce heating bills and qualify for potential rebates.
A roof window on a flat roof is also a smart ventilation solution for bathrooms, stairwells, or kitchens where natural airflow reduces moisture buildup.
Cost Factors in Toronto
The cost to install or replace a flat roof skylight in Toronto ranges from $1,200 to $3,500+, depending on size, style, roof accessibility, and whether any structural work is required.
While basic fixed dome skylights are cheaper, opening skylights and roof windows with insulated glass tend to pay off in energy savings over time.
For a tailored quote, companies like Flat Roof Toronto offer free inspections and expert recommendations on placement, model selection, and installation methods suited to your roof type.
Maintenance Tips
To keep your flat roof skylight leak-free and functional:
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Clean debris from surrounding roofing membrane and skylight frame
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Inspect seals and flashing annually
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Reseal with compatible materials every few years
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Don’t step on domed skylights—they’re not designed to support weight
Regular maintenance can extend the life of your skylight and prevent costly roof repairs.
Conclusion
Adding or replacing a flat roof skylight is an excellent investment for Toronto homes and commercial buildings. It improves lighting, adds ventilation, and increases property appeal. But the key to success lies in proper planning, quality materials, and expert installation.
Avoid shortcuts, choose trusted brands like VELUX and Columbia, and partner with experienced contractors like Flat Roof Toronto for waterproof, long-lasting results.