ODOT catch basin No. 2-4 dimensions: the verified numbers
The ODOT catch basin No. 2-4 has inside dimensions of 4 feet by 4 feet, designed for outlet pipes from 30 to 36 inches, with 8 inch nominal walls that precast producers may reduce to a 6 inch minimum while holding the inside dimensions. Those numbers come straight from the current ODOT Standard Construction Drawing CB-2-3, 2-4 (revision 7-19-2024), and this post gives you the rest of the sheet: the full 2-N family ladder, wall and grate details, the renumbering trap that sends people to dead drawing references, and what a producer actually quotes against this designation.
The current SCD, and the renumbering trap
ODOT renumbered its catch basin standard drawings around 2021, and half the references you will find online still point at the old ids. The No. 2-4 basin lives on the drawing now titled CB-2-3, 2-4; the same drawing was historically CB-1.2. If a plan set or a county spec references CB-1.2, it means this sheet. The current revisions worth writing down:
- CB-2-2A, 2B, 2C, revision 7-19-2024 (was CB-1.1): the 2 ft x 2 ft family
- CB-2-3, 2-4, revision 7-19-2024 (was CB-1.2): the 3x3 and this 4x4
- CB-2-5, 2-6, revision 7-19-2024 (was CB-1.3): the 5x5 and 6x6
- CB-3 and CB-3A, revision 1-16-2026 (were CB-2.1 and CB-2.2): the curb inlets
All of them are free, versioned PDFs in ODOT's Standard Hydraulic Construction Drawings library.
No. 2-4 dimensions and details
| Item | Value | Source |
|---|---|---|
| Inside dimensions | 4'-0" x 4'-0" square | SCD CB-2-3, 2-4 rev 7-19-2024 |
| Outlet pipe range | 30" to 36" | same SCD |
| Walls | 8" nominal; precast minimum 6", reduced from outside | same SCD |
| Top opening | 2'-3 1/2" square grate opening | same SCD, shared with the 2-2 and 2-3 basins |
| Grate | 120 lb minimum, steel; bicycle-safe options per plan | same SCD |
| Steps | Required over 6 ft deep | same SCD |
| Traffic rating | Not a roadway structure; use the curb inlet series in pavement | same SCD |
A vendor cross-check is worth doing on any spec number, so we did one: Scioto Valley Precast publishes a 4x4 Catch Basin ODOT 2-4 CB shop sheet showing 48 by 48 inches inside, 6 inch walls, a 60 inch square outside, a 48 inch base section with 12 inch risers, and a 24 by 24 grate with EJ 5110 castings. It matches the SCD exactly, and it is marked special order, which tells you something real: the 4x4 is not a shelf item at most yards, so lead time belongs in your quote conversation.
The full 2-N ladder, because plans mix designations
The 2-N family is a size ladder, and once you see the pattern the designations stop being memorization. The 2-2A, 2-2B, and 2-2C are all the same 2 ft x 2 ft box; the suffix only changes the top configuration (side-inlet ditch top, flat grate, or the parking-lot casting with a concrete apron). From 2-3 upward, the number is the inside dimension in feet.
| Designation | Inside | Outlet pipe range |
|---|---|---|
| No. 2-2A / 2-2B / 2-2C | 2' x 2' | 12" to 18" |
| No. 2-3 | 3' x 3' | 12" to 27" |
| No. 2-4 | 4' x 4' | 30" to 36" |
| No. 2-5 | 5' x 5' | 42" to 48" |
| No. 2-6 | 6' x 6' | 54" to 60" |
One estimating gotcha that costs real money: a designation with a dash is a catalog size, and a dimension with an x is a measurement. No. 2-3 is a 36 by 36 inch square basin; a callout reading 2x3 is a 24 by 36 inch rectangular inlet. Our takeoff system treats the dash and the x as different grammars for exactly this reason, and it is the kind of trap we test for explicitly in our accuracy benchmark.
Beyond the squares: the curb inlet drawings you will see next to a 2-4
Plans that carry a No. 2-4 usually carry its curb-and-gutter cousins on the same schedule, so the neighboring designations are worth having in the same note. The CB-3 curb inlet (revision 1-16-2026) runs 4 feet 9 inches by 2 feet 3 inches inside on the standard drawing, with a cast-in S6x12.5 steel beam spanning 6 feet across the throat; be aware that common precast versions of the box run 60 inches long rather than the drawing's 57 inch cast-in-place interior, a small discrepancy that matters if you are matching an existing structure. The smaller CB-3A (same revision date) is 2 feet 2 inches by 2 feet 3 inches inside with a 3 foot 6 inch beam, and it is the designation municipalities most often modify, which is why you will see callouts like ODOT Mod. No. 3A on city work.
The median and ditch series rounds out the family: the No. 4 median basin at 5 feet 4 inches by 2 feet 8 inches inside, the No. 5 ditch basin and No. 8 median basin both at 2 feet 8 inches square, and the No. 6 curb basin at 3 feet by 1 foot 6 inches with a 72 inch maximum depth. Every one of them follows the same precast rule as the 2-N ladder: the drawing's nominal walls cover cast-in-place construction, and precast is permitted at 6 inch minimum walls with the inside dimensions held. If your estimator keeps one cheat sheet taped to the monitor, it should be this family table plus the revision dates, because a plan referencing a stale drawing id is the first clue the designer worked from an old spec.
What this means when you quote one
Three practical notes from the producer side. First, the SCD walls are 8 inch nominal because the drawing covers cast-in-place and masonry construction; precast is explicitly allowed at 6 inch minimum walls with inside dimensions held, so a 4x4 precast box at 6 inch walls is a 60 inch outside square, which drives your form, your weight, and your truck math. Second, the outlet range on the sheet (30 to 36 inch) is the fastest sanity check on a plan callout: a No. 2-4 receiving a 12 inch pipe is legal but suspicious, and a No. 2-4 with a 42 inch outlet is a misread or a mislabel, worth a question either way. Third, depth drives accessories: steps over 6 feet, and sump depth per the plan detail rather than assumption.
When a plan calls a modified designation, like the ODOT Mod. No. 3A you will see on some municipal work, the Mod is the part to price carefully: it is the delta between the standard drawing and that agency's or producer's variant, and it is not on the ODOT sheet. Flag it, ask, and quote what is printed. That habit, printed values or explicit questions, is the entire discipline behind accurate takeoffs, whether a human or a purpose-built AI is doing the reading.
FAQ
What size is an ODOT No. 2-4 catch basin? 4 feet by 4 feet inside, square. Precast versions run 6 inch minimum walls (60 inch outside square); the drawing's nominal 8 inch walls cover cast-in-place construction.
What pipe sizes can connect to a No. 2-4? The standard drawing assigns it a 30 to 36 inch outlet range. Smaller laterals can enter per the plan, but the outlet range is the designation's defining spec.
Which ODOT drawing covers the No. 2-4? SCD CB-2-3, 2-4, revision 7-19-2024, in ODOT's Standard Hydraulic Construction Drawings. Older references call the same sheet CB-1.2.
Is the No. 2-4 a curb inlet? No. The 2-N family are grate catch basins for ditches, yards, and parking areas. Curb-and-gutter work uses the CB-3 and CB-3A curb inlet drawings.
Do precast producers stock the 4x4? Often not; vendor sheets commonly mark it special order. Confirm lead time before you promise a delivery date on a bid.
Put it to the test
If your estimators are reading designations like this off civil sets all day, that reading is exactly what our Custom AI Employee does, with every value traced to the printed sheet and every uncertainty flagged as a question. Send two or three plans you already quoted through the Plan Challenge and compare the takeoffs against your own numbers tomorrow.