You notice water below a skylight and assume rain has entered through the roof. Then it happens again on a day without rain. Should you replace the skylight, repair the flashing or investigate moisture inside the house?
Water around a skylight can have several causes. The glazing, opening seals, surrounding roof details and indoor conditions may all need consideration. Where the water appears is useful information, but it does not establish the source by itself.
Before approving a repair, document when the moisture appears and ask what evidence supports the diagnosis. That can help you avoid paying for work that leaves the original problem unresolved.
Start with when and where the water appears
The timing often provides better clues than the stain alone.
Does water appear during rainfall, after snow melts, on cold mornings or after someone showers? Is it on the room-facing glass, around the frame, or on the wall below the opening?
Record the pattern without trying to reach the skylight. Take photographs from a safe indoor position and note the weather and room conditions.
Useful details include:
- Whether rain was falling when the water appeared
- Whether there was snow or ice on the roof
- Whether droplets were visible on the inside glass
- Whether the skylight was open or closed
- Whether nearby rooms were unusually humid
- Whether this is a new problem or a recurring one
These observations help guide the assessment. Several causes can overlap, so a pattern should be treated as a clue rather than proof.
What is the difference between condensation and a leak?
Condensation forms when moisture in the air collects on a sufficiently cold surface. A leak involves water entering through a defect or an unintended opening.
VELUX identifies condensation as a possible explanation for a skylight that appears to leak even when it is not raining. Its service guidance notes that condensation can occur in cold or humid conditions and may produce dripping.
That does not mean every dry-weather drip is condensation. Water from an earlier event may still be present, and other moisture sources may need investigation.
Likewise, droplets during a rainy period do not automatically establish a roofing leak. The assessment should consider both the indoor conditions and the skylight assembly.
Ask the contractor which observations support the proposed explanation and whether anything remains uncertain.
Is moisture on the glass different from moisture between the panes?
Yes. The location changes what needs checking.
Droplets on the accessible room-facing surface may be consistent with condensation. Cloudiness that appears enclosed within the glazing needs a different assessment.
Describe what you can see without dismantling the unit or climbing to touch it. Does the mist disappear during the day? Does it appear trapped inside? Is the view permanently cloudy?
For a glazed unit, ask whether the glazing assembly, its seals or another component needs attention. The available repair options depend on the skylight’s make, model and condition.
Do not assume that fogging requires replacement of the entire roof opening. Equally, cleaning the visible glass will not address moisture enclosed within an inaccessible part of the assembly.
What does skylight flashing do?
Flashing forms part of the weather-protection arrangement where the skylight meets the roof. Its configuration needs to suit the skylight, roof covering and installation conditions.
VELUX describes its flashing systems as designed to shed water without relying on exposed sealants that can deteriorate over time.
For an existing installation, the useful question is whether the surrounding details are appropriate and intact—not simply whether someone can apply more sealant.
An assessment may need to examine:
- Flashing around the skylight
- Connections with adjacent roofing
- The condition of the mounting curb or frame
- Accessible waterproofing details
- Previous repairs around the opening
Ask which parts were visible and which remained concealed. A contractor should distinguish a confirmed defect from a detail that needs further investigation.
Why is adding sealant not always enough?
A surface bead of sealant may not correct an underlying installation or roofing problem.
If water is entering through an incorrectly formed junction, replacing only the visible sealant may leave the water route unchanged. If the issue is condensation, exterior sealant will not address the indoor moisture conditions.
Before approving another sealing visit, ask:
- Where is water believed to be entering?
- What evidence supports that location?
- Is the proposed treatment temporary or permanent?
- Does the work correct the underlying detail?
- What happens if the moisture returns?
A temporary measure may be appropriate while further work is planned. Its purpose and limitations should be clear.
Repeated sealing without a documented diagnosis is a reason to request a fuller assessment.
Could the surrounding roof be the problem?
A stain beside a skylight does not prove the skylight itself has failed.
The assessment should include the nearby roofing and relevant junctions, rather than treating the unit as isolated from the rest of the roof.
Tell the contractor about recent roof repairs, equipment installations or other work nearby. Share previous photographs and invoices if you have them.
If a broader roof inspection is recommended, ask which additional areas need checking and why. This helps establish whether the concern involves the skylight, surrounding roof or both.
Replacing the unit without understanding the adjacent conditions may leave an unresolved source of water entry.
What should be checked on an opening skylight?
For a skylight that opens, explain whether it closes fully and whether the problem occurs only under certain conditions.
Mention sticking, uneven closure, damaged visible seals or an operating mechanism that no longer works as expected. Do not force the unit closed or attempt to dismantle high-level hardware.
The inspector may need the product identification to establish which parts and instructions apply. If a label is safely accessible, photograph it. Otherwise, leave identification to the person assessing the unit.
A repair proposal should explain whether it addresses operation, weather sealing or another component. Restoring an opening mechanism and repairing surrounding flashing are different tasks.
When might repair be appropriate?
Repair may be practical when a specific defect is identified and the remaining skylight and roof details are suitable to retain.
Examples to discuss include a localized flashing correction, an available replacement component or repair to the surrounding roofing. The appropriate option depends on the findings and product requirements.
Ask what will remain in place after the repair and whether its condition was assessed. If components are unavailable or the assembly has several problems, that may affect the recommendation.
Apple Roofing’s skylight services include inspection, repair, installation and replacement. The proposed work should follow the condition of your existing installation.
When does replacement make more sense?
Replacement may be worth considering where the unit is damaged, suitable parts are unavailable, or its condition makes further repair impractical.
Ask for the reasons rather than relying on age alone.
A replacement discussion should establish:
- The existing unit’s type and dimensions
- Whether the current curb or opening can be retained
- Compatibility with the roof covering and slope
- The proposed flashing arrangement
- Any interior finishing work required
If you are also planning roof replacement, discuss the skylight at the same time. Ask whether retaining it is practical and how the surrounding details will be handled.
Coordinating the work can help clarify responsibilities, but a roof replacement does not automatically mean every skylight needs replacing.
Compare proposals by the problem they address
Two skylight quotes may cover very different work.
| Proposed work | What to clarify |
|---|---|
| Flashing repair | Which detail will be corrected and what surrounding roofing is included |
| Component replacement | Which part is being replaced and whether it suits the existing model |
| Full skylight replacement | Unit, flashing, opening preparation and interior work included |
| Condensation investigation | Which indoor or assembly conditions need further assessment |
| Temporary leak protection | Intended purpose, limitations and permanent follow-up |
Ask whether damaged interior finishes are included or require another contractor. Clarify how concealed damage discovered during the work would be documented and priced.
For roof leak repair, make sure the scope distinguishes confirmed findings from further investigation.
What should you do while waiting for assessment?
If water is actively entering, report that when booking. Describe the amount, location and whether it is affecting electrical fittings or a bulging ceiling.
Protect belongings only where it is safe. Avoid touching wet electrical equipment, and keep away from unstable ceiling areas.
Do not climb onto the roof, lean out through the skylight or conduct your own hose test. Keep a record of further moisture events instead.
Before repainting stained finishes, establish whether the moisture source has been addressed and whether the affected materials are ready for reinstatement.
Plan the repair around the findings
For a Toronto home, send us safe indoor photos, a short description of when the moisture appears and any records of previous skylight or roof work.
We can assess the accessible conditions and discuss whether the next step involves the unit, surrounding roofing or further investigation.
Request a free quote from Apple Roofing to plan your skylight assessment, repair or replacement.
Frequently Asked Questions
Can condensation make a skylight appear to leak?
Yes. Moisture can collect on cold surfaces and may drip, particularly under cold or humid conditions. Record when and where it appears. An assessment should distinguish condensation from exterior water entry rather than relying on timing alone.
Will adding sealant stop a skylight leak?
It depends on the cause. Sealant alone may not correct a flashing, roofing or installation defect, and it will not address condensation. Ask where water is entering and how the proposed work addresses that finding.
Does a leaking skylight always need replacement?
No. A repair may be suitable if a specific defect can be corrected and the remaining assembly is serviceable. Replacement depends on the unit’s condition, available components and installation requirements.
Roman is the founder of Apple Roofing, leading the company with a clear focus on quality workmanship, reliability, and customer satisfaction. With years of experience in the roofing industry, he has helped build Apple Roofing into one of Toronto’s trusted roofing companies, delivering durable, long-lasting roofing solutions for homeowners and businesses.
