Skylight Curbs and the Glazing Perimeter
A skylight sits on a curb, and the leak usually appears at one of three places: the upslope corner, where water collects against the curb with nowhere to go; the base flashing, where the membrane meets the curb face; and the perimeter of the glazing, where the gasket or sealant has aged. The upslope corner is the most common, because a curb without a cricket behind it creates a small dam, and standing water finds any weakness in the corner.
We inspect each curb for the height of its flashing above the roof surface, the integrity of the counterflashing or cap, and the condition of the glazing seal. Where flashing is too short we raise it and rebuild the termination, and where a cricket is missing we add one so water is sent around the curb. On older glass or acrylic domes that have yellowed, cracked or crazed, we recommend replacement of the unit with the curb detail, since a new flashing around a failing dome solves only half the trouble.
Formed Flashing Versus Sealant
Sealant has a place on a roof, as a finishing joint where two well-fitted pieces meet. It is a poor substitute for the pieces themselves. A bead packed around a penetration skins over in the heat, shrinks as it cures, and opens a hairline gap that grows as the roof moves. A formed flashing that sheds water by its geometry does not depend on that bead.
We make flashings from the membrane itself where the system allows, with factory-formed corners, welded or bonded laps and a clean termination at the top. At walls and curbs we use sheet metal counterflashing set into a reglet or lapped over the curb, with a tooled joint to finish the line. Metal flashings that must be fitted to an odd shape are hand-formed on the roof or fabricated from a template, then soldered at the seams. That fit and finish takes longer than a caulk gun, and it is the reason the detail is still tight after the next summer.
Heat, Embers and Thermal Movement
Heat does most of the damage to flashing in this climate. Roof surfaces here bake through a long dry summer, and a heat advisory in October 2023 still brought highs near 100 F, which means rubber, mastic and sealant spend much of the year at stress. Curbs and pipes expand and contract at different rates than the membrane around them, and the flashing at their base takes that movement every day. We choose materials for their heat tolerance and leave the movement room that a rigid detail would not have.
Roof openings also matter in fire country. In the fire zones the city has mapped, generally in the Arroyo Seco and upper Hastings Ranch, ember-resistant vents and Class A roof assemblies apply wherever the Very High tier does, and skylights and penetrations must be dealt with in that context. We confirm the requirements for the address before we finalize any detail near the roof edge or around a vent, since an opening that lets embers in defeats a good roof covering.
Roof Terraces, Gardens and Busy Campus Roofs
Mixed-use buildings carry some of the most complicated roof penetrations. Plaza Las Fuentes has roof terraces and gardens beside its hotel and office tower, and a terrace roof carries planters, railings, hatches and mechanical stacks. Paseo Colorado, opened in 2001, packs roughly 600,000 square feet of commercial space and nearly 400 residential units onto three downtown blocks, and it mixes uses in the same way. Every railing post, planter drain and stair bulkhead needs flashing, and a roof that people use is walked on far more than a service roof.
On campuses and hospitals, such as those in the HeArt district around Huntington Hospital, penetrations can multiply with every renovation, and old, abandoned ones are sometimes left open or half-sealed. We survey the penetrations on a roof, remove what is dead, flash what remains, and keep a record that feeds the preventive maintenance visits that follow, so the next contractor does not drill through a roof without knowing what lies below. Where equipment sits on curbs, the flashing is reviewed together with the rooftop equipment curbs and supports beneath it, so the equipment and the roof are treated as one.
Commercial Roofing Questions
Why does my skylight leak only when it rains hard?
Heavy rain can back water against the upslope corner after a light shower runs off. We check the curb, cricket, and perimeter seal for a short flashing or a joint that has pulled away.
Can I reseal around a leaking vent pipe myself?
A fresh bead can slow a leak briefly, but sealant on an aged boot will fail again as soon as the sun softens it. The fix is a new boot or formed flashing with a clamp at the top and a welded or bonded base. That takes a short visit and keeps the leak from returning.
Do I need to replace the entire skylight, or just the flashing?
If the glazing is cracked, clouded or no longer seals, replacing the unit with the flashing is the better purchase. If the dome or panel is sound and the curb flashing has failed, rebuilding the flashing is enough. We check the glass and gaskets before we decide, and show you the findings.
How do you protect the space below while you work?
We cover floors and equipment, work in short sections, and close the opening before leaving. In a medical or laboratory space, facilities staff set the access and timing requirements.
What if I find old penetrations that nobody uses?
Abandoned pipes, conduits and brackets are common, and each one is a leak waiting to happen. We confirm with your facility team that they are dead, cut them back below the surface, and close the opening with a patch that is flashed into the membrane. For buildings that may add panels later, clean penetrations also leave a clearer deck for solar-ready roofing.
