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A skylight that appears to be leaking is not always leaking. Interior moisture at a skylight can result from condensation on the glazing unit, a failed glazing seal between the panes, a compromised flashing assembly, or a frame failure -- and each of those causes requires a completely different response. PDM Roofing identifies the actual source before any repair begins.
Counter-flashing and step-flashing failure at skylight curb or deck-mount frame -- the most common true water infiltration source and the most frequently misdiagnosed.
Failed perimeter seal between glazing and frame allows water entry at the glass edge -- requires sealant or glazing replacement, not roofing work.
Moisture on or between glazing panes from temperature differential -- not water infiltration; requires ventilation or IGU (insulated glass unit) evaluation.
Cracked or degraded skylight frame allows water to track into the curb area -- may require unit replacement rather than repair.
Why Skylight Repair Requires Precise Diagnosis
Applying sealant around a skylight curb when the actual failure is in the flashing integration below the roofing surface will not stop water from entering. Replacing flashing when the issue is interior condensation on the glazing will not eliminate moisture. The diagnostic step is the most critical part of skylight repair -- and it is the part most often skipped.
One of the most common misunderstandings in skylight troubleshooting is treating condensation as equivalent to active water infiltration. Condensation occurs when warm interior air contacts a cold glazing surface and the moisture in the air drops out as liquid on or between the panes. It appears on the interior face of single-pane skylights when indoor humidity is high and exterior temperatures are low, and it appears between the panes of older double-glazed units when the perimeter seal of the insulated glass unit (IGU) has failed, allowing moist air into the space between the panes. Neither of these conditions indicates that rain is entering the building through the skylight assembly. Addressing them requires improved interior ventilation, reduced indoor humidity, or IGU replacement -- not roofing flashing work.
When a skylight is genuinely allowing rain water into the structure, the failure is most commonly in the flashing assembly -- not in the skylight unit itself. Skylights are integrated into the roof system through a combination of step flashing along the sides, head flashing above, and apron flashing below. Over time, these flashing components can lift, separate, corrode, or lose the sealant that prevents water from tracking beneath them. Curb-mount skylights are additionally susceptible to failure where the counter-flashing at the top of the curb meets the step flashing in the roof plane. A correctly installed new skylight placed on a repaired or replaced flashing assembly will perform reliably; a new skylight installed without addressing failed flashing will leak in the same location within the first rain event.
Not every skylight repair is cost-effective. Older units with degraded frames, failed IGUs, or cracked glazing may reach a point where the cumulative cost of repairs approaches or exceeds the cost of a properly installed replacement unit. We provide an honest evaluation of this question based on the unit's age, condition, and the nature of the failure. When replacement is the better long-term decision, we can coordinate the full scope -- unit selection, removal of the existing skylight, curb preparation or modification, new unit installation, and complete flashing integration into the existing roofing system so the repair is done correctly from the structural level outward.
Curb-mount skylights sit on top of a raised curb frame that is built into the roof deck opening, with the skylight unit resting on and secured to the curb's top perimeter. Deck-mount skylights (also called flange-mount or self-flashing skylights) sit directly in the roof plane with a flange that integrates with the roofing material below. These two configurations have different flashing assemblies, different common failure points, and require different repair approaches. A repair plan that does not account for which type is installed will not address the correct failure zone. Curb-mount units fail most commonly at the curb-to-flashing interface; deck-mount units fail most commonly at the flange-to-shingle integration and at the head flashing above the unit.
Skylight Mount Types
Understanding which skylight type is installed in your Plainsboro home or commercial building shapes every aspect of the repair approach.
Unit sits on a raised structural curb
A curb-mount skylight rests on top of a wood or metal curb frame that is built directly into the roof deck opening, typically 4 to 6 inches above the surrounding roof surface. The counter-flashing at the curb top and the step flashing at the sides of the curb create the weatherproofing interface between the unit and the roof system. Curb-mount installations are common on low-slope roof sections and for larger custom skylight openings where a structural curb provides a stable mounting platform.
Common failure points include the curb-to-counter-flashing seal at the top of the curb, step flashing integration along the curb sides, and the apron flashing and head flashing at the uphill face of the curb where water is most forcefully directed during rain events.
Flanged unit integrates directly into roof plane
Deck-mount or self-flashing skylights have an integrated metal flange that sits beneath the roofing material in the surrounding field, with a raised perimeter curb that is part of the skylight unit itself rather than a separate framing component. Deck-mount units are the most commonly installed type in residential construction and are typically found in standard pitch roof slopes between 14 and 85 degrees. Major manufacturers produce pre-fabricated flashing kits that integrate with specific roofing materials, and proper installation depends on correct layering of shingles, flashing components, and the skylight's own water management features.
Common failure points include the head flashing and saddle at the uphill edge of the unit, the side step flashing-to-shingle integration, and the sill flashing below the unit where wind-driven rain can force water upward against gravity.
What We Do
Active inspection during or after rainfall conditions to identify true infiltration source versus condensation. Interior moisture pattern analysis cross-referenced with exterior flashing and frame condition assessment.
Step flashing, counter-flashing, head flashing, and apron flashing repair or replacement at curb-mount and deck-mount units. Correct integration with existing roofing material to restore weather-tight performance.
Perimeter frame-to-glazing seal replacement when water is tracking through the seal rather than through flashing. Correct sealant selection for glazing material type to prevent adhesion failure and UV degradation.
IGU seal failure identification and glazing unit replacement for fogged or moisture-laden double-pane skylights. Ventilation recommendations when condensation results from interior humidity levels rather than glazing failure.
Curb structural evaluation and repair for curb-mount units where frame degradation is contributing to water entry at the curb interface. Counter-flashing and coping repair to restore curb-top weather protection.
Full coordination of unit selection, removal, opening preparation, new unit installation, and flashing integration for skylights that have reached end of serviceable life. Handled as a complete roofing system repair, not a product swap.
Our Approach
Interior moisture evidence documented and classified as condensation, glazing-related infiltration, or flashing-related infiltration. This classification determines the entire repair direction -- roofing work addresses flashing failures; frame and glazing work addresses unit-level failures; condensation requires a different response entirely.
Full exterior inspection of the skylight assembly: flashing components, frame perimeter seal, curb condition (if applicable), and roofing surface integration at all four sides of the unit. Photographs taken of all observed defects to document the condition and support the repair scope discussion.
Written repair scope provided with an honest assessment of whether repair is appropriate or whether unit age and condition make replacement the more cost-effective choice. No pressure toward either option -- the goal is the right long-term decision for your property.
Flashing reintegration, glazing seal repair, or full unit replacement executed correctly and with appropriate attention to water management at each component. Post-repair inspection confirms the repair is complete before we leave the property. Follow-up contact after the next significant rainfall event to confirm performance.
Customer Feedback
"I had a contractor tell me my skylight needed to be replaced entirely. PDM Roofing came out and spent time actually diagnosing the problem -- turned out the head flashing had lifted about a quarter inch and was allowing water to run behind it during heavy rain. They repaired the flashing integration and reseated the counter-flashing. That was months ago and the skylight has been completely dry since. I appreciate that they didn't just sell me a replacement unit I didn't need."
"We had what looked like moisture damage below our skylight and assumed it was leaking. PDM Roofing's technician identified it as condensation from the fogged IGU between the panes -- the seal had failed years ago. They sourced a replacement IGU for the unit and installed it. Interior moisture is completely resolved. A completely different fix than 'reseal the flashing' -- which is what two other contractors had suggested without actually looking at the unit."
"Our deck-mount skylight had been showing water infiltration for two seasons. Previous attempts to seal around it from outside just didn't hold. PDM Roofing pulled back the shingles at the step flashing on the upper-right side and found that a section of step flashing had been installed incorrectly from the original installation -- the lap was reversed. They re-did the step flashing correctly, replaced the shingles, and re-sealed the perimeter. No water since. That's the level of diagnostic work that actually solves the problem."
Common Questions
Where We Work
PDM Roofing provides accurate skylight leak diagnosis and correct repair -- whether the issue is flashing, glazing, condensation, or frame failure. Serving Plainsboro, NJ. Call +1-855-469-0306 today.
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