Fog trapped between skylight panes usually means the insulated glass unit’s edge seal has failed, allowing moisture into the space between the glass. Unlike condensation on an accessible surface, this moisture cannot be wiped away. Replacing the affected glass unit, or the skylight when necessary, is generally the lasting solution.
November and December often make the problem more noticeable. Cold outdoor temperatures encourage moisture inside compromised glazing to condense. The skylight may appear clear during certain hours and cloudy during others. Temporary clearing, however, does not necessarily mean the seal has recovered.
Is It Failed Skylight Seals or Surface Condensation?
Before arranging repairs, identify where the moisture appears. These three situations require different responses:
- Interior condensation: Moisture forms on the glass facing the room and can usually be wiped away when safely accessible.
- Exterior condensation: Moisture develops outside the skylight under certain weather conditions.
- Between-pane fogging: Haze, droplets, or streaks remain inside the sealed glass assembly and cannot be reached by cleaning.
Only check the interior glass if you can reach it safely. Do not climb onto the roof. Photograph the fogging and note whether it follows cold nights, bathing, cooking, or rainfall.
Why Do Skylight Seals Fail?
Insulated glazing depends on a sealed perimeter to keep moisture out. Repeated temperature changes, installation stresses, weather exposure, and material deterioration can eventually compromise that perimeter.
When moisture enters, the unit’s moisture-absorbing material can become overwhelmed. Condensation then develops between the panes. In gas-filled units, seal failure may also allow insulating gas to escape, reducing the glazing’s original thermal performance.
This differs from damaged flashing. Flashing directs roof water around the skylight opening. A skylight can have foggy insulated glass without leaking rainwater. Similarly, roof-related leakage can occur while the glass remains clear.
Can Cleaning or Caulking Remove the Fog?
Cleaning accessible surfaces will not remove moisture trapped inside insulated glazing. Adding caulk around the outside does not reconstruct the factory-made glass seal or restore lost insulating gas.
Defogging treatments may improve appearance in some situations, but cosmetic clearing should not be confused with restoring the original glazing system. Before approving treatment, ask:
- Does it restore the sealed glass assembly?
- Will insulating performance be restored?
- Could fogging return?
- What does the warranty cover?
Avoid drilling glass, applying improvised sealants, or covering drainage openings. These shortcuts can create additional problems without resolving the failed seal.
Should You Replace the Glass or the Skylight?
Glass replacement may be appropriate when compatible glazing is available and the frame, operating components, and roof connection remain sound. This approach addresses the failed insulated unit without automatically replacing everything.
Full replacement becomes more compelling when the frame is deteriorated, hardware is failing, leaks recur, or replacement glass is impractical. The skylight’s age and overall condition should guide the decision.
Check existing warranty coverage before approving work. Installation records, manufacturer information, photographs, and approximate age can help clarify the available options.
What Should You Do Before Winter?
Record changes in visibility and report ceiling stains, active drips, cracked glass, or damp trim separately. These symptoms may indicate problems beyond glazing failure. Arrange an assessment before assuming that humidity control, fresh caulk, or cleaning will solve the issue.
Discuss Your Skylight With Aluplex
Contact Aluplex to discuss persistent fogging, suspected failed skylight seals, or an aging unit before winter conditions complicate repairs. The company offers residential and commercial skylights, repair, installation, and replacement services. Explain whether the haze is trapped between panes and mention accompanying leaks or operating problems.
Request an assessment to understand whether replacement glazing or a new skylight better suits the existing installation, rather than choosing a cosmetic treatment that leaves the underlying issue unresolved.
