Skylight Curb Flashing Repair
The skylight curb is a raised frame, typically wood or metal, that elevates the skylight above the roof surface to prevent water from ponding against the glazing base. The roofing membrane is flashed up the curb face and lapped under the skylight's sill flashing. This membrane-to-curb transition is where most roofing-side skylight leaks originate.
Curb flashing failure modes include: membrane base flashing that has separated from the curb face due to adhesive failure or freeze-thaw cycling; sealant at the top termination of the base flashing that has dried out and cracked; metal counter-flashing that has lifted off the reglet in the curb; and improper original installation where the base flashing does not lap under the sill at the manufacturer-required height.
We repair curb flashings to the membrane manufacturer's published skylight detail. On buildings where the original installation does not match current detail requirements, common on older commercial buildings in Clayton and Downtown St Louis, we bring the termination into compliance rather than patch the existing failing configuration.
Glazing Seal and Frame Joint Repair
The glazing seal, the bedding compound that seals the glass or polycarbonate panel into the skylight frame, deteriorates under UV exposure and freeze-thaw cycling. In commercial skylights, glazing seal failure typically presents as visible cracking or extrusion of the existing sealant, or as water entry that tracks from the frame interior rather than from the curb area.
Glazing seal repair requires removing the existing sealant completely, cleaning the glazing and frame surfaces to remove contamination and old sealant residue, and applying fresh sealant compatible with both the glazing material and the frame. The correct sealant chemistry matters, silicone and polyurethane sealants have different adhesion requirements against glass, polycarbonate, aluminum, and galvanized steel, and using the wrong product produces a bond that fails faster than the original.
Frame corner joints and screw penetrations through the skylight frame are secondary sources of water entry. We inspect all frame penetrations and joints and reseal as needed with compatible exterior-grade sealant.
Condensation and Drainage at Skylights
Commercial skylights in occupied buildings produce condensation on the interior glazing surface during cold weather, the temperature differential between the warm interior and the cold glazing drives condensation that can be mistaken for a roof leak. Genuine skylight leaks follow rain events; condensation is most pronounced during cold, dry weather when heating systems are running hard.
Skylight frames that are designed to manage condensation have internal drainage channels that direct condensate to the building interior without allowing it to puddle at the sill. When these drainage channels are clogged, typically with dust, mineral deposits, or debris from the glazing installation, condensate overflows the channel and appears as a water leak at the skylight perimeter.
We check condensate channel function on every skylight service call and clear them if needed. Identifying condensation as the source of apparent leaking prevents unnecessary roofing work and correctly directs the building team to the HVAC or building envelope solution.
Hail Damage to Skylights
St Louis's active hail season produces direct impacts on skylight glazing. Polycarbonate glazing panels, common on industrial and warehouse skylights, are more hail-resistant than glass but develop surface crazing after repeated impacts that eventually compromises UV stability and leads to yellowing and brittleness. Glass skylights in commercial applications can fracture under large hail.
After a significant St Louis hail event, we include skylight inspection in our post-storm roof assessment. Impact damage to the glazing itself is a glazing contractor scope for panel replacement; impact damage to the frame, curb, and surrounding membrane flashing is our scope. We identify the boundary clearly and coordinate with the glazing contractor where both trades need to be involved.
Hail Damage Assessment on St. Louis Commercial Skylights
Missouri's hail frequency means commercial skylight glazing in St. Louis faces above-average annual impact exposure. After significant hail events, glazing panels that sustain stone impacts may fracture or develop structural micro-cracking that reduces their resistance to subsequent impacts. We inspect commercial skylight glazing within 48 hours of significant St. Louis hail events as part of post-storm assessment, documenting hard-surface impact evidence on metal components and assessing the glazing structural condition.
Acrylic glazing on older St. Louis commercial skylights, already UV-degraded from Missouri's summer solar exposure, is particularly vulnerable to hail fracture because the UV degradation has consumed the material's impact reserve. Post-hail skylight assessment on buildings with older acrylic glazing often identifies panels that were technically intact before the event but had insufficient structural reserve to survive the impact without fracture.
