Flashing Failure Repair in Daly City, CA

Sealant on a failed flashing is a bandage, and a roof that keeps needing it has a detail problem. On commercial roofs in Daly City, CA, most flashing trouble sits where the roof meets something else: a parapet, a wall, a curb, a pipe, a drain or a skylight. We begin at the interior leak report and go up to the nearest transition, then look at the membrane, the termination and the counterflashing as a system. Cracked sealant, a gap at the top edge, a pulled-away corner or a flashing that no longer reaches the height it was set to are the usual signs. We photograph each failure and measure it, because the repair depends on whether the flashing moved, shrank, tore or was never terminated well.

The next decision is whether to reseal, reflash a section or rebuild the detail.

Flashings fail for different reasons, and repeating the original detail repeats the failure. Thermal movement pulls a flashing off a wall in cold mornings and pushes it back by afternoon. Membrane shrinkage tightens the sheet and lifts the base. Fasteners back out of a termination bar, sealant dries and splits, and counterflashing slips. Roof traffic bends edges and cuts corners. Water running down a wall can get behind the counterflashing if the reglet is open. We note which of these is at work, because it determines whether a patch will hold. A flashing that has pulled back because the membrane shrank needs more than new sealant; it needs a new piece of membrane with enough slack to move.

Water that enters at a flashing rarely shows up directly below it. It runs along the deck or between insulation boards before dripping into the building, so the stain can be many feet from the failure. We use the interior report as a starting point and follow the water path upslope. Where insulation near the flashing is wet, we cut it out and replace it before closing the detail, or the moisture will return to the new membrane and loosen the bond.

The top of a base flashing is where most leaks begin. We look at how the flashing ends: under a metal cap, in a reglet, under siding or behind a coping. A termination bar should be tight, sealed and fastened at the right spacing. A counterflashing should lap over the base flashing by enough to shed water. We probe the wall behind the flashing for rot or softness, especially where a parapet meets a roof corner. Along Mission Street, in Westlake and in Serramonte, every building has its own wall, so we inspect each wall type for what it is. Brick, stucco, metal panel and concrete all call for different terminations and different sealants.

A pipe boot cracks in the sun. A curb flashing splits at the corner. A skylight flashing leaks where its flange meets the membrane. We treat each penetration as a separate repair. Pipe penetrations often need a new boot or a pourable sealer pocket, depending on spacing and the shape of the pipe. Curbs need corner patches that tie the flashing into the field membrane, and the curb or support may need to be reset if it has shifted. Skylight and hatch flashing may need the frame resealed or the flashing replaced. The repair is photographed from the same angle before and after.

Clusters need extra care. Where several pipes, conduits and supports come through the roof in one place, flashings overlap and a gap hides between them. We map the cluster, remove old sealant that has hardened, and rebuild the area with a single continuous flashing where possible. Fewer seams mean fewer places for water to enter, and the finished area is easier to inspect from year to year.

The San Francisco International Airport station averages 19.64 inches a year, 16.76 of them from November to March and 0.18 across June, July and August. Flashing repairs need dry surfaces and a cure period, so the dry summer is when most detail work is done well. A failed flashing in winter gets a temporary seal that holds until conditions allow a permanent repair, and a crew can be sent at any hour if water is coming in. We tell the owner what the temporary work is and when we plan to return. The temporary seal is documented so it is not left as the final repair by mistake.

A sound flashing with a small gap can be resealed with a compatible sealant and a fresh termination. A flashing with several cracks or a loose base is better reflashed with new membrane welded or adhered to the roof, then terminated at the wall with a bar and sealant. A liquid-applied flashing resin can handle irregular shapes, such as multiple pipes in a cluster, where cut membrane would be awkward. The choice depends on the existing membrane: EPDM uses different adhesives and tapes than a thermoplastic sheet. Where the detail has failed more than once, we rebuild it, replacing the substrate and setting the height and slope correctly. A base flashing should rise high enough above the roof surface to stay clear of standing water and drifting debris, and the cant strip at the base should hold the membrane at a gentle angle instead of a sharp fold. We check those two dimensions on every rebuilt wall detail and record them on the plan.

Closeout: Mark every repaired detail on the plan

At completion, we photograph each repaired flashing from the roof surface and from a distance, and we mark it on the roof plan. The record lists the material used, the height, the termination and any adjacent items left alone. A flashing map is useful at the next inspection, since it lets a reviewer check the same details against the first photographs. Related work, such as a seam repair near the flashing, is listed on the same plan. Properties in San Bruno, where San Mateo Avenue is a commercial street, and in other Peninsula cities receive the same record. Edges lifted by wind are recorded the same way, with the flashing and the edge metal shown together.

Commercial Roofing Questions

Can I just recaulk a leaking flashing?

Sometimes, when the flashing is sound and the gap is small. If the flashing has moved, shrunk or torn, caulk will fail again, and the repair should address the movement.

Why does the same corner leak every winter?

A corner concentrates movement and water, and it is easy to build badly. We check the corner membrane, the fasteners and the wall above, and we rebuild it with reinforcing pieces rather than adding more sealant.

How long does a flashing repair take?

Small repairs take hours; a full rebuild of a parapet can take days. The time depends on the length, the wall type and whether the work has to wait for a dry day. We give the building contact the expected duration and any area that must stay clear while sealants cure.

Does a flashing repair affect the roof warranty?

Some manufacturers specify how repairs are made. We note the existing roof system and use compatible materials, and we leave a record the owner can share.

Is a permit required for flashing work?

A minor repair may not need a permit. When a scope reaches wall or structural changes, the Building Division and its Title 24 review come into play, and we confirm the path before work starts.