Skylight andPenetration Flashing

Skylight and Penetration Flashing failures are among the most consistent leak sources on Tacoma commercial buildings — not because the flashing work is inherently difficult, but because the details that matter most are executed once at installation and then subject to years of thermal cycling, UV degradation, and the sustained moisture load that Pacific Northwest weather delivers. On Port of Tacoma facility buildings and Frederickson Industrial Center warehouses with dense HVAC and exhaust penetration layouts, getting every curb flashing right across dozens of penetrations requires systematic execution, not spot attention to the obvious ones while the rest go unverified.

Frederickson Industrial Center buildings and Tideflats manufacturing facilities regularly carry 30 to 60 rooftop penetrations — HVAC units, exhaust fans, make-up air units, electrical conduit stacks, plumbing vents, process exhaust stacks, and specialty equipment specific to the building's manufacturing or logistics use. Each penetration requires a watertight curb flashing that extends the roof membrane up and over the equipment curb and terminates under a counterflashing or reglet that prevents water from entering above the membrane termination. When we walk those roofs and probe every penetration in sequence, we routinely find five to ten flashing conditions that are either open at the lap, have lost sealant at the termination bar, or have a corner that was never properly sealed at installation.

Curb flashing integrity is the specific detail that Pacific Northwest sustained rain tests most severely. A curb corner that appears to be sealed with a small bead of lap sealant may hold through the brief, intense rain events that dominate some other markets. In Tacoma, that same corner is subjected to days of continuous wetting, and any small void in the sealant becomes a capillary water entry path that steadily wets the insulation below. We flash curb corners with full membrane gussets — not sealant alone — because a properly executed membrane corner is mechanically bonded to the substrate and does not rely on sealant continuity for its watertight performance.

Historic Downtown Tacoma buildings and older Stadium District commercial properties frequently have skylights that were installed in the original construction — cast-iron framed industrial skylights, steel wire-glass units, and mid-century aluminum-framed ridge skylights that define the character of those buildings but have long since exceeded their expected service life. Re-flashing a historic skylight without replacing the glazing assembly requires careful sequencing: the existing frame must be examined for structural integrity, the curb below the frame must be sound, and the new flashing must integrate with the existing frame in a way that provides a watertight seal without damaging the historic components. We have re-flashed original industrial skylights on Pacific Avenue buildings and in Old Town Tacoma that are a century old — the work is more deliberate than standard curb flashing but the result preserves building character that replacement skylights cannot replicate.

Pipe boot flashings — the flexible rubber or metal collars that seal around plumbing vents, conduit stacks, and small-diameter penetrations — have a defined service life that is shorter than the roof membrane itself. Standard EPDM pipe boots on Pacific Northwest roofs typically begin showing UV cracking and collar degradation at 12 to 18 years. On south- and west-facing roof slopes that take the direct exposure of Tacoma's prevailing storm track, degradation appears earlier. We inventory and replace aged pipe boots as a standard element of any re-roofing or re-cover scope, and we identify and replace failed boots on maintenance visits before they become active leaks.

Pitch pans — the metal pockets filled with pitch or sealant around irregularly shaped penetrations that cannot be flashed with a standard boot or curb — are maintenance items that require periodic sealant replenishment. The fill material in a pitch pan shrinks and cracks over time, pulling away from the penetration and leaving a gap at the top of the pocket that admits water. On industrial buildings with process piping and structural steel penetrations that are too complex for standard curb flashing, pitch pans are sometimes the only practical flashing option. We check and re-fill pitch pans on every maintenance visit and flag any pans that are large enough to require complete reconstruction rather than simple sealant replenishment.

Curb height is a detail that matters more on Tacoma roofs than on buildings in drier climates. Industry standards call for a minimum eight-inch curb height on rooftop HVAC equipment — enough clearance for the membrane to terminate well above the roof surface and remain above standing water during rain events. On Tacoma's low-slope roofs where ponding is common and October through January storms can leave two to four inches of standing water in low areas for 24 to 48 hours, a six-inch curb is marginal and a four-inch curb is asking for water entry at the membrane-to-counter flashing termination. When we find low-curb equipment installations during inspections, we note the condition and recommend curb height extension where the mechanical system configuration allows.

Seismic considerations affect penetration flashing design on Tacoma commercial buildings — Pierce County's seismic hazard classification means that rooftop equipment is seismically braced, and the bracing hardware penetrates the roof membrane alongside or adjacent to the equipment curb. Each brace penetration through the membrane is a flashing requirement. On older buildings where seismic bracing was added to existing equipment as a retrofit, the brace penetrations were sometimes not properly flashed at the time of installation. We include brace penetration flashing in our inspection checklist on any building that has undergone seismic retrofit work.