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If you’re researching how to install a skylight on a flat roof, the basic process involves cutting an opening in the roof, building a raised curb, installing the skylight, and sealing everything properly to keep water out. It sounds simple, but one small mistake can lead to leaks, which is why many homeowners choose professional installation instead of tackling it themselves.
Key Takeaways:
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Before you start, make sure you have the right tools and materials. Running back and forth to the hardware store halfway through the project isn’t much fun.
Tools You’ll Need
Materials You’ll Need
One thing many first-time DIYers don’t realize is that flat roof skylights need a raised curb. Think of it like a small frame that lifts the skylight above the roof surface. Without it, rainwater and melting snow can sit around the skylight and eventually find a way inside.
That’s especially important here in Southeastern Wisconsin, where roofs deal with everything from summer storms to winter snow.
Start by deciding where you want more natural light.
Many homeowners choose areas like:
Take a look at your ceiling and roof structure before picking a spot. You don’t want to discover a plumbing vent or HVAC duct right where the skylight needs to go.
Once you’ve picked the location, measure carefully.
Then measure again.
And maybe one more time.
Seriously, most skylight installation problems start with bad measurements. Follow the dimensions provided by the skylight manufacturer and mark the opening clearly with a chalk line.
Taking an extra 10 minutes here can save hours of frustration later.
Now it’s time to create the opening.
Remove the roofing material in the marked area and carefully cut through the roof deck.
This part makes a lot of homeowners nervous, and that’s understandable. You’re literally cutting a hole in your roof.
Work slowly and stay focused. If you’re not comfortable working at heights or using power tools overhead, it may be time to call a professional.
After cutting the opening, you’ll need to reinforce it with framing. This is important in how to install a skylight on a flat roof.
The framing supports the skylight and helps maintain the roof’s strength.
Depending on your roof layout, you may need to add headers between roof joists. This step is crucial because you don’t want the roof structure weakened after the skylight is installed.
This is what makes flat roof skylights different from many other skylight projects.
The curb is a raised frame built around the opening.
A properly built curb should:
In Wisconsin, snow can sit on roofs for days or even weeks. A raised curb helps keep melting snow from working its way into the skylight opening.
Next, wrap the curb with roofing membrane.
This membrane acts as a waterproof barrier between your roof and the skylight.
Take your time here. Corners and seams need extra attention because these are the areas where leaks often begin.
Many skylight leaks aren’t caused by the skylight itself. They’re caused by shortcuts taken during waterproofing.
Now comes the exciting part.
Place the skylight on top of the curb and secure it according to the manufacturer’s instructions.
Check that it sits evenly on all sides before tightening everything down.
Don’t rush this step. A crooked skylight can create problems with sealing and flashing later.
Flashing helps direct water away from the skylight.
Think of it as your skylight’s first line of defense against rain and snow.
Most skylights come with flashing kits that are designed specifically for that model.
Follow the instructions carefully and install each flashing piece in the correct order.
Skipping steps here is one of the quickest ways to end up with a leak.
Once the skylight is secured and flashed, seal all recommended joints and gaps.
After that, add insulation around the skylight frame.
This helps:
This step matters even more during cold Wisconsin winters when warm indoor air meets freezing outdoor temperatures.
Before you call the project finished, inspect your work.
Look for:
Many roofing professionals also perform a water test to make sure everything is watertight.
It’s much better to find a problem now than during the next thunderstorm.
Even good-quality skylights can cause problems if they’re installed incorrectly.
Here are some mistakes to watch out for.
A flat roof skylight should never sit directly on the roof.
Without a curb, water can collect around the skylight and eventually leak into your home.
Cutting the wrong-sized opening can create a lot of extra work.
Always double-check measurements before making any cuts.
Flashing protects your roof from water intrusion.
If flashing is installed incorrectly, even a brand-new skylight can leak.
A skylight installed in the wrong spot may not provide the natural light you were hoping for.
Take time to consider the sun’s path and any nearby obstacles.
A skylight that works well in a warm climate may need additional protection in Southeastern Wisconsin.
Snow, ice, rain, and freeze-thaw cycles can all affect long-term performance.
Most flat roofs can support a skylight, but the structure should be evaluated first. Roof condition, framing, and drainage all play a role in determining whether installation is possible.
Most skylight installation projects take one to three days. Larger projects or interior finishing work can add extra time.
Not if they’re installed correctly. A properly built curb, quality flashing, and good waterproofing greatly reduce the chance of leaks.
If you have roofing and carpentry experience, it can be. For many homeowners, hiring a skylight installation company is the safer and less stressful option.
Look for a contractor with experience working on flat roofs, positive customer reviews, and a history of successful skylight installation projects. Don’t be afraid to ask for references and photos of previous work.
Adding a skylight is one of the best ways to bring natural light into your home. But when it comes to how to install a skylight on a flat roof, getting the details right matters. One missed step can lead to leaks, water damage, and expensive repairs.
At M&L Siding and Services, we help homeowners with roofing, siding, windows, and skylight installation projects. Whether you’re planning a new skylight or need advice from an experienced contractor, we’re here to help.
Contact us today for a professional consultation and discover whether a new skylight is the right fit for your home.