Skylights and Roof Leaks: Common Problems

Q: Why do skylights leak?

Most skylight leaks are flashing failures, not skylight unit failures. The flashing system around the skylight frame — step flashing on the sides, head flashing above, and sill flashing below — is what keeps water out. When this flashing deteriorates or was improperly installed, water enters around the frame even if the glazing itself is intact. The second most common cause is condensation on the interior side, which can look like a leak but is a ventilation issue.

Q: How do I tell if a skylight leak is from the glass or the flashing?

Water entering through the glazing (cracked glass, failed seal) is relatively rare. Check the seal perimeter inside: if it is cracked or the frame shows rust, the unit itself may be compromised. More commonly, water appears to drip from the skylight frame edges or at the corners — this indicates flashing failure around the unit. A contractor can run a water test to isolate whether the problem is the unit or the flashing.

Q: When should a skylight be replaced rather than re-flashed?

Replace the skylight if: the unit is more than 20 years old, the glazing has yellowed or cracked, the frame shows significant rust or deformation, there is visible damage to the thermal pane seal (fogging between panes), or re-flashing has been done before and the leak returned. If the unit is sound and the leak is isolated to flashing, re-flashing alone is often sufficient.

The Most Common Skylight Leak Cause

When water appears near a skylight, most homeowners assume the skylight unit itself has failed. In most cases, the actual problem is the flashing system around the skylight — not the glass or unit. Skylight flashing fails for the same reasons any other flashing fails: age, improper installation, or storm damage.

How Skylight Flashing Works

A properly installed skylight has a multi-component flashing system:

Sill flashing: A pan flashing at the bottom of the skylight frame that catches any water getting past the unit and directs it out
Step flashing: Individual L-shaped metal pieces interleaved with shingles on the sides of the skylight
Head flashing: Flashing above the skylight that diverts water around the top corners
Counterflashing: A second flashing layer that caps the step flashing and is sealed against the skylight frame

Any failure in this system creates a water entry point. Single-piece "flashing kit" installations that come with lower-cost skylights are more prone to failure than custom-fabricated step flashing systems.

Condensation vs. Leak: How to Tell

Skylights can develop interior "wetness" that is not actually a leak from outside:

Condensation: Moisture forms on the inside of the skylight in cold weather when warm interior air meets the cold glass surface. This appears as dripping or wetness during cold snaps, not during rain. Solution: improve attic ventilation and interior humidity control.
True leak: Water appears during or after rainfall, not correlated with temperature. May appear at the frame edges or drip from the corners of the skylight opening.

Skylight Flashing Repair Costs

Re-sealing minor flashing gaps: $200-$500
Partial re-flashing with shingle repair: $400-$900
Full skylight re-flashing (removing shingles and installing new flashing system): $600-$1,500
Skylight replacement (unit + flashing + shingles): $1,200-$3,500 depending on unit size and type

Preventing Skylight Leaks

Have skylights inspected as part of any roof inspection
Look for lifting or damaged shingles adjacent to the skylight frame
Check interior frame edges for rust staining or water marks annually
When replacing the roof, always re-flash all skylights — reusing old flashing is a common contractor cost-cutting measure that leads to callbacks

Related: How to Find a Roof Leak

Frequently Asked Questions

Why do skylights leak?

Most skylight leaks are flashing failures, not unit failures. The flashing system around the skylight frame deteriorates over time. Condensation on the interior side can also mimic a leak but is a ventilation issue, not a roof problem.

How do I tell if a skylight leak is from the glass or the flashing?

Water at frame edges or corners usually indicates flashing failure. Water through the glazing itself is rare. A contractor can run a water test to isolate the source.

When should a skylight be replaced rather than re-flashed?

Replace if the unit is 20+ years old, the glazing is yellowed or cracked, the frame shows significant rust, or the thermal pane seal has failed (fogging between panes). If the unit is sound, re-flashing alone is often sufficient.

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This page is for general informational purposes only. Leak diagnosis requires professional inspection. Consult a licensed roofing contractor for an accurate assessment of skylight leak sources and repair options.