Commercial Roofing Services
Rooftop Equipment Curbs and Supports in Federal Way, WA
Counting the units comes first on a curb job, and the superintendent marks each one on the roof plan. Every rooftop unit sits on a curb or a rail, every curb is a hole cut into the membrane, and every hole is a place the weather tests. A Federal Way, WA roof with ten units has ten tie-ins to build and ten more to close before evening. The order we work in decides whether the crew finishes dry.
After the count comes the walk. We check curb height against the roof surface, look at the flashing on all four sides, pull on the counterflashing and note any pipe or conduit support resting directly on the membrane. Then we settle the crane pick, the lay-down yard and the dry-in plan before a unit moves.
How tall does a curb need to be?
The curb has to rise far enough above the finished roof surface for the base flashing to turn up and be fastened with room to spare. When a recover or a thicker insulation package raises the roof, the curb loses some of that rise. A curb that cleared the old membrane by eight inches may clear the new one by four, and four is not enough for a sound flashing detail.
We measure each curb from the deck and from the surface, then compare the numbers with the new build-up. If the rise falls short, the choices are to raise the curb, reset the unit on a taller one or extend the flashing with a compatible accessory. The choice depends on the unit, the duct connections and the crane time available. Washington's amended 2021 International Building Code and the 2021 commercial energy code settle the insulation thickness in the scope, and that thickness sets how much curb rise is needed.
On a roof in the Federal Way City Center area, the same measuring routine applies: we shoot the curb height at every unit, record it on the plan and keep the numbers for the closeout walk. If the roof later receives an insulation or cover board upgrade, the record shows which curbs were already marginal, so nobody finds out on the lift day.
What about pipe and conduit supports?
Pipes and conduit that cross a roof need supports, and supports that sit straight on the membrane wear it through. We look for sleeper blocks, rollers and stands with a protection pad, and we check whether the pad has worn through. A support with no pad is a puncture waiting for foot traffic to finish it.
The fix is a set of supports designed for roof use, with a base that spreads the load and a pad that can be replaced. For gas lines and refrigerant runs, we coordinate with the mechanical trade so a support is not moved without the line being checked. Where pipes enter the roof, we replace tired boots with prefabricated or field-formed flashings, and we tag each one on the plan. A penetration flashing done correctly on day one does not need another visit.
What is the sequence on a curb replacement?
First we confirm shutdown windows with the building. The unit is disconnected, the crane is booked and the curb is exposed. Next comes the temporary seal over the opening, because a rooftop unit swap leaves a hole that must be covered the moment the unit lifts. Then the old curb is removed, the deck is checked, the new curb is set and fastened, and the flashing is built up to the surface.
The unit goes back on the new curb during the same pick when the schedule allows. If the unit cannot return the same day, we dry in the curb with a cap and photograph it. Closeout walks cover each curb one at a time: counterflashing seated, sealant tooled, fasteners set, unit gasket compressed. The day-one punch list names anything left open, and the superintendent signs it before the crew leaves.
How does the wet season change the plan?
Rain falls hardest in the Green River corridor from November into December, where Auburn totals 37.1 inches a year, while Tacoma logs about 40.8 inches over roughly 155 wet days. A curb job done in July has time to cure and cool between steps. One done in November does not. In the wet months, we size the open area to what we can seal by evening, and we stage materials under cover.
Wind belongs in the plan, too. A storm like the November 2024 bomb cyclone, which put 74 mph winds on Enumclaw, tests curb flashings first, and a loose cap is the first thing to lift. We fasten caps and counterflashings as if that wind is returning, and we check them after any storm. A wind-damaged roof repair often starts at the curbs.
Where do curb jobs come up around here?
Pacific Highway South, the city's main commercial strip, and The Commons indoor mall are the kind of retail stock that carries rooftop units, and the Pavilions Centre strip mall raises the same questions in smaller bays. At the Woodbridge industrial park, built on part of the former Weyerhaeuser campus, and at warehouses in the Kent Valley, Auburn and Fife, the walk counts the units and measures the pipe runs the same way. Healthcare buildings, with St. Francis Hospital and the Virginia Mason medical center as local examples, typically carry their own shutdown rules for unit work.
Each building sets its own schedule. A retail lot needs the lay-down yard away from customer parking, and a hospital needs the shutdown agreed with facilities. We walk the sequence with your superintendent before a number goes on paper. For a larger group, a multi-site roof program lets us plan curb work across buildings. Owners in Kent and Auburn get the same plan, and the crew leader assigned to the job carries the curb list from the first walk to the final photograph.
Commercial Roofing Questions
Can a unit be replaced without opening the roof to rain?
Yes, if the crane pick, the temporary seal and the new curb are planned as one sequence. We cover the opening the moment the unit lifts and keep the cover on until the new unit sits. In the wet months we also hold the work when the forecast shows rain before the seal can go on.
What happens if the new unit has a different footprint?
The curb is rebuilt or adapted to the new unit, and the deck opening is checked for framing. We get the unit dimensions and weight before the pick, confirm support with the structural drawings or an engineer where needed, and flash the new curb as a fresh detail.
Do abandoned curbs need to be removed?
Remove them or cap them with a proper deck-level closure. A dead curb with a failed seal leaks like a live one. We list each abandoned item on the plan and price the closure separately, so the owner can see what is being removed and what is being kept.
How tall is tall enough for a curb after a recover?
Enough that the base flashing can turn up the curb with room for fasteners and sealant above the new roof surface. We measure after the new build-up is known, then raise or extend as needed.
Should the mechanical contractor be on site for the pick?
Yes. The mechanical trade handles disconnects, gas, refrigerant and controls, while we handle the roof. A shared schedule with named contacts keeps the pick on time and the opening covered.
Send the roof plan and the unit schedule
Send the roof plan, the unit list and the project schedule so we can walk the sequence, staging and tie-ins with your superintendent before a number goes on paper.
