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If you’re staring at a failed rooftop unit on an older Jersey City commercial building and the new RTU footprint doesn’t match your existing curb, you already know the answer isn’t “order a standard adapter off a shelf.” There is no standard. Every legacy curb is its own situation.
I’ve been fabricating custom roof curb adapters out of our Kearny shop since 2015, and the single biggest source of delays isn’t fabrication time. It’s incomplete field data. Contractors show up with one dimension, maybe two photos taken from bad angles, and a model number that’s been painted over twice. That’s not enough to cut steel to tolerance.
So let me walk you through what the ordering process actually looks like when it’s done right, starting with what you need to pull from the roof before you call anyone.
The existing curb is your governing dimension. Not the new RTU spec sheet. Not the architectural drawing from 2003. The curb sitting on that roof right now.
Here’s what needs to come off that roof before we can fabricate anything:
Photos from all four sides, plus straight-down shots of the duct openings. I can’t stress the photos enough. What gets me is when a contractor sends a single diagonal photo taken from six feet away. I can’t read dimensions from that, and I don’t guess.
Dense Hudson County rooftops — think Hoboken, Weehawken, North Bergen — often have gas risers, conduit, adjacent units, and parapet walls sitting close enough to create real staging headaches. Document every obstruction within four feet of the existing curb. If a parapet wall cuts into the crane swing path, that changes the lift plan, and that needs to be known before crane day, not during it.
Once you have the existing curb dimensions locked, pull the new RTU’s base rail dimensions from the manufacturer’s submittal. The adapter bridges these two geometries. Its job is to transition the old curb footprint to the new unit’s mounting pattern without disturbing the ductwork below.
What information do you need to order a custom curb adapter for an RTU replacement? You need the existing curb length, width, and height; supply and return opening dimensions and positions; the new RTU base footprint and mounting hole pattern; roof type; nearby obstructions; and photos from multiple angles. If the curb runs out of level, that must be documented because the adapter has to compensate for it structurally.
The adapter height is where I see most projects get stuck. Mechanical clearance between the unit and the roof surface, structural load distribution, and drainage all depend on getting that height right. If the adapter is too tall, you’ve created a thermal bridge and potential wind uplift point. Too short, and the unit can’t drain properly or seal against the curb flange.
Our CNC plasma tables and Accurpress system handle these transitions accurately, but only if the incoming data is clean. An eighth-of-an-inch error in the field measurement becomes an eighth-of-an-inch error in steel, and on a crane day with six mechanics on the clock, that’s a very expensive morning.
Once you’ve collected the field measurements, photos, and new RTU spec sheet, the submission process is straightforward. We built our intake around mechanical contractors who don’t have time to fill out a seven-page form.
Send us:
We turn around estimates using digital estimating software that ingests your takeoff data and returns hard numbers — not ballpark ranges — within 4 to 24 hours. While other supply houses are still playing phone tag and hand-calculating on graph paper two days later, your estimator already has a line-item quote tied to actual curb dimensions, material spec, and height transition requirements.
Drawings get issued after we verify the curb data. Not before. I’m not going to release shop drawings based on a guess.
This is where local environment actually matters. Rooftops along the Hudson River waterfront — Port Jersey, the Jersey City shoreline, Bayonne near the Kill Van Kull — take consistent salt-laden air exposure. For those sites, galvanneal or a heavier-gauge galvanized steel is the right call, not the lightest spec that passes a visual inspection. We process 18 to 26-gauge galvanized, stainless, and aluminum depending on structural load limits and corrosion exposure. Aluminum is increasingly popular for rooftop adapter work because it keeps the added load off older roof decks. This breakdown on ductwork material selection goes deeper if you’re deciding between metal options for a specific application.
Short answer: yes, if the geometry aligns. That’s the whole point of a properly engineered curb adapter.
The ductwork below the curb stays untouched. The existing curb stays in place. The adapter sits on top of the curb and accepts the new RTU’s base rail. One lift, one connection, minimal roof disturbance. That’s the clean scenario.
Where things go sideways is when someone tries to stack a second adapter on top of an existing adapter that was already installed for a previous unit swap. I’ve seen this on older commercial stock in Kearny and Secaucus, where a building goes through two or three RTU cycles without anyone pulling the previous adapter off. You end up with a tower of mismatched steel, compromised gasket seals, and a structural load that nobody’s engineer has reviewed. That’s a liability problem, not just an aesthetic one.
If you discover an existing adapter on the curb during your site survey, document its dimensions and condition separately. We’ll determine whether the new adapter can work off the existing curb directly, or whether the old adapter needs to come off first.
Fabricating the adapter is only part of the project. Getting it to the roof on the day your crane is scheduled is where most commercial HVAC retrofits either hold together or fall apart.
A Saturday rigging permit in Jersey City near the Route 440 corridor has specific lane restriction windows. Miss the morning staging window because your fabricated adapter is sitting on a freight dock somewhere in the Meadowlands waiting for a third-party carrier, and you’ve lost your crane window. That permit doesn’t reschedule for free. Neither does your crew.
Our in-house box truck fleet runs deliveries as early as 6:00 AM from our facility at 181-183 Garfield Ave, Kearny, NJ 07032. The adapter, gasket material, and any accessory hardware ship together. One delivery, one invoice, no scrambling to source sealant from a separate supplier while your crew stands on the roof waiting.
How early can fabricated curb adapters be delivered to a Hudson County job site? We dispatch from Kearny and can reach most Hudson County sites by 6:00 AM using our own fleet. That timing is designed specifically to beat traffic on the Pulaski Skyway and Route 1/9 approaches, so your crew and crane can start the moment the shift opens, not after a late freight truck finally shows up.
Most contractors don’t want to manage four separate POs for one rooftop swap. We bundle the custom adapter with the gasket, fasteners, and sealant specified for the roof and curb type. If you need equipment rails or a transition plenum to tie the new unit back into the existing duct system, those get fabricated and shipped together. More on how we handle the full RTU replacement package is here.
Every curb adapter we fabricate goes through a dimensional and structural check before it hits the plasma table. That’s not a sales pitch — it’s just how you avoid building something that fails a city inspection or creates a wind uplift failure on a waterfront roof in February.
For Hudson County commercial properties, particularly pre-war and mid-century buildings in Hoboken and downtown Jersey City, the roof deck load limits are often underdocumented. If you’re adding height to the curb through the adapter (which effectively changes the lever arm against wind load), a structural engineer review of the assembly is worth the cost. We can work from engineer-stamped drawings or provide shop drawings for your engineer to review before fabrication starts.
Our fabrication complies with SMACNA standards and NJ UCC building code requirements. That matters when the Jersey City building inspector shows up and wants to see documentation. SMACNA-compliant fabrication specs are built into every adapter we produce, not added as an afterthought.
Does a custom roof curb adapter require a structural engineer review before installation? Not always, but on older commercial rooftops with unknown deck load ratings, or when the adapter adds significant height to the existing curb assembly, having a structural engineer review the combined load is the right call. We produce shop drawings that support that review process.
I’ll be direct about what consistently derails adapter orders, because watching the same problems repeat across different contractors gets old.
One thing I genuinely don’t understand is why some contractors still rely on supply houses that take three days to return a quote on a non-standard part. The competitive bid environment in this market doesn’t support that kind of lag. We return estimates in 4 to 24 hours on adapter orders because that’s the speed the work actually moves at.
If you’ve got a curb survey done or you’re in the middle of one, reach out now. The sooner we have the field data, the sooner drawings get issued and steel gets cut.
You can submit measurements, photos, and project notes directly through our contact page. If you’re not sure whether you’ve captured everything you need from the roof, our estimating team will walk through your documentation before the quote goes out.
We’re also active on LinkedIn and Facebook if you want to see recent fabrication work or ask a quick question before committing to a formal submittal.
The crane window doesn’t care if your adapter is ready. We do.
Written by: Arthur Dabrowski
HVAC Metals, LLC
(201) 991-2206