The Approved Submittal That Still Did Not Fit
Why this matters
A submittal stamped No Exceptions Taken feels like permission to stop thinking about the equipment. It is not. The reviewer checked the product against the design intent; nobody on the design side checked whether this exact unit, with these options and these accessories, fits the curb, the roof structure and the screen it is going into. That check is the contractor's, and when it is skipped the discovery comes at the worst possible moment, with the unit on a flatbed and a crane on the clock. This case starts at that moment, because that is where the decisions that cost the most get made, and then traces how an approved submittal carried a unit 19 percent over the roof's limit.
The morning of the set
An HVAC shop was replacing rooftop unit RTU-3 on an occupied single-story retail building. The plan was a same-day swap: crane at 8 AM, old unit off, adapter curb and new unit on, store cooling again by mid-afternoon. The old unit was still running.
At 7:40 the crane operator asked the lead for the pick weight of each lift, including the adapter curb that sat on the flatbed beside the unit. The new unit needed an adapter because its footprint differed from the existing curb's. The lead read the adapter's shipping label, 250 lb, and the unit's weight from the submittal, and called the project manager (PM) to confirm the total for the lift plan. While on the phone, the PM opened the structural sheet for the first time on this job. S-101 carried a note from the engineer who had evaluated the roof for the replacement: RTU-3 operating weight, including any curb adapter, not to exceed 2,400 lb.
The PM added it up on the call and told the lead to hold the lift.
Containing it before anyone diagnosed anything
The safety call came first and was not negotiable. Nobody sets a unit onto a roof whose structure has not been confirmed for its weight; a joist overloaded at a point load is not a problem you find later, it is a collapse risk over a sales floor full of people. The lift was held, the crane's swing area stayed barricaded, and no one stood under any suspended load while the crew re-secured the unit on the truck. The old unit stayed in service, so the store kept its cooling.
The options, each priced in time and in multiples:
| Option | What it costs | What it risks |
|---|---|---|
| Set it anyway | Nothing today | Overloaded structure, a code violation, the shop's liability |
| Return the unit, order the basis-of-design unit | A restocking charge stated by the supplier as a percentage of the unit, plus about 8 weeks of lead time | Summer without a new unit; old unit runs another season |
| Store it, ask the engineer to evaluate the real load | The crane's minimum hours paid today for no lift, a second crane day later, storage | Reinforcement may be required, and someone pays for it |
The shop took the third option. The crane left after its minimum charge. The unit and adapter went to the supplier's yard. The PM sent two RFIs that afternoon, one to the structural engineer with the actual operating weight and the adapter weight, one to the architect about height, for a reason that came out an hour later.
What the approved submittal actually said
The spec named a basis-of-design unit and two other acceptable manufacturers. The shop had submitted one of the others. The package came back from the mechanical engineer stamped No Exceptions Taken, with the stamp's standard language: reviewed for general conformance with the design concept; the contractor remains responsible for dimensions, quantities, fabrication, coordination with other trades and conformance with the contract documents. See related: What a Submittal Review Stamp Means and What It Does Not, which is the card on what that language does and does not transfer.
The mechanical reviewer checked what a mechanical reviewer checks: capacity, efficiency, the economizer, the reheat option, the electrical characteristics. The structural engineer was not on the review routing for mechanical product data. And the adapter curb was not in the package at all; the shop had ordered it from the supplier separately as an accessory.
Tracing the weight
RTU-3 WEIGHT, AS OFFICE READ IT vs AS SHIPPED
(lb, from the submitted weight table)
office read: base unit, operating 2,180
against S-101 limit 2,400
"fits, 220 lb to spare"
as shipped: base unit, operating 2,180
economizer + 190
hot gas reheat + 160
high-input gas heat + 85
unit with options 2,615
adapter curb + 250
total on structure 2,865
S-101 limit 2,400
over by 465
465 / 2,400 = 19.4 percent over
The number that lied was 2,180. It was the first weight on the cut sheet, labeled operating weight, and it was the weight of the base unit with no options. The options the spec required, and the shop had correctly submitted, were each listed in a separate accessory weight table two pages later. Whoever compared the unit to the structure, if anyone did, compared the base number to a limit that explicitly included the adapter. The submittal itself was accurate. Every number needed to see the problem was in the package or on the flatbed label; nobody added them against the one sheet that set the limit.
The basis-of-design unit, for comparison: 2,250 lb operating with the same options, on the existing curb with no adapter. Under the limit by 150 lb. The engineer had sized the limit around it.
Tracing the height
The architect's RFI came out of the same afternoon. The lead, holding the adapter, measured it at 14 in tall, and remembered the equipment screen on the roof, a wall that hides the units from the street. The architectural elevation called the screen 5'-0" above the roof.
- Basis of design: existing curb 14 in + unit 44 in = 58 in, 2 in below the 60 in screen.
- As submitted: existing curb 14 in + adapter 14 in + unit 48 in = 76 in, 16 in above the screen.
The unit's height was on the submitted cut sheet. The adapter's height was not in the package. The screen's height was on an architectural sheet nobody on the mechanical side had reason to open. Three facts on three documents, each correct, never set side by side.
How it resolved, in hours and days
The structural engineer's answer came in 6 working days: the roof could carry 2,865 lb at that location with two joists reinforced, a detail they issued with the answer. The general contractor's (GC) steel subcontractor installed it in the following week. The architect accepted an 18 in extension of the screen on that face, which the GC's framer built.
The set happened 17 working days after the first crane day. The shop paid two crane days for one lift. Under its subcontract the shop also bore the reinforcement and the screen extension, because the conflict came from the product the shop selected, not from the design. That allocation was the GC's reading of the stamp language and the subcontract, and it is the common one; your own documents decide yours, and this is not legal advice. The old unit ran through the delay without failing, which was luck rather than planning.
The check the shop now runs before it submits
Every piece of equipment that lands on something existing, or on something another discipline designed, gets a fit sheet filled in and signed by the PM before the submittal leaves, with the lead's field measurements attached. The fit sheet goes into the package, so the reviewer sees it too. Each row names the controlling document by sheet, the limit, the submitted value with all options and accessories included, and pass or fail. Here is the sheet as it would have read for RTU-3:
EQUIPMENT FIT CHECK RTU-3 prepared by PM
row check source limit submitted P/F
1 footprint field meas existing adapter P*
of curb curb req'd
2 weight incl S-101 note 2,400 2,865 lb F
options+adpt
3 top height A-201 elev 60 in 76 in F
above roof screen
4 service mfr manual 48 in 52 in P
clearance vs parapet
5 elec MCA E-101 sched 50 A 42 A P
vs breaker ckt
6 gas input P-201 as same P
vs pipe existing sized input
* adapter adds weight and height: carry to 2 and 3
Rows 2 and 3 fail, and either one stops the submittal. A failing row has three ways out, all before the package goes: change the selection (here, submit the basis-of-design unit, which passes both), ask the engineer or architect by RFI whether the limit can move, or submit with the fit sheet showing the failure and the RFI number, so the reviewer and the GC know the approval depends on the answer.
Three habits the sheet enforces:
- Weight is summed from the options table, never read from the first line. The base operating weight is the start of the arithmetic, not the answer.
- Accessories ordered outside the package count. An adapter, roof rails, a vibration isolation base or a sound blanket all sit on the structure and change the height.
- Every limit is found on its own sheet. Structural notes, architectural elevations and the electrical schedule are opened deliberately, because the reviewer will not open them for you. See related: How to Prepare a Submittal for Your Own Scope, and How to Field-Verify Existing Conditions Before You Order.
When the same stamp would have been enough
On a new building where the design team sized the curb, the structure and the screen around the submitted unit, the contractor's fit check is still owed but is far less likely to find anything. It is in replacements, substitutions and or-equal selections, where the product changes and the existing conditions do not, that a correct submittal and an approved stamp most often carry a unit that does not fit. The shop's rule now treats any non-basis-of-design selection on existing structure as a fit sheet that must pass before submitting, not after.
References
- See related: What a Submittal Review Stamp Means and What It Does Not
- See related: How to Prepare a Submittal for Your Own Scope
- See related: How to Field-Verify Existing Conditions Before You Order
- See related: Specification Compliance and the Or Equal Question
- See related: The Submittal Log SOP