Construction glossary · Sitework
What is catch basin in construction?
A catch basin in construction is a precast concrete inlet structure with a grate on top that collects surface runoff and feeds it into the storm drain system, with a sump below the outlet pipe to trap sediment. Estimators count catch basins each (ea), grouped by depth class, because the vertical feet from rim to invert drive the price more than anything else. Each one appears on the civil utility and grading plans with a rim elevation and invert elevations for its pipe connections.
Updated June 2026 · Reviewed by the Ruh construction team
How catch basins are counted
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Book a walkthroughA catch basin is the workhorse inlet of site storm drainage: runoff sheets across pavement to a grate, drops into the structure, and exits through an outlet pipe set above a sump that traps sediment and debris. On the documents it lives on the civil utility plan and grading plan, each structure tagged with a rim elevation and invert elevations, backed by a detail or a structure schedule on the C-sheets, and the site utility sub typically owns the scope. A catch basin is an assembly of components: a precast base section, riser sections to reach grade, grade rings for final adjustment, and a cast iron frame and grate, with traffic rated frames specified in drive lanes. The mistake new estimators make is counting basins as identical units. A basin with 9 ft from rim to invert carries far more excavation, precast, and backfill than a 4 ft one, and a curb inlet frame is a different casting than a flat grate. Group the count by depth class and frame type before pricing, the same way the precast supplier will quote it.
Catch basins are counted each (ea), but the count only prices correctly when it is grouped by depth class, typically in 2 ft steps such as 0 to 6 ft, 6 to 8 ft, and 8 to 10 ft. Depth is rim elevation minus the lowest invert elevation, both printed on the utility plan or structure schedule, plus the sump depth from the detail. Vertical feet drive cost because every added foot means another precast riser section, more trench excavation, and more backfill. The frame and grate is a separate component spec (flat grate, curb inlet, traffic rated), and the connecting pipe is never included in the structure price; it is taken off separately in lf.
Worked example
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How Ruh handles catch basin
Ruh pulls rim and invert elevations off the contractor's utility plan, computes the depth of every catch basin, and builds the count by depth class with frames and grates broken out. Those quantities price against the contractor's own price book, and the draft estimate goes to the estimator for review and sign off.
See AI construction takeoff and estimating softwareCatch basin: frequently asked questions
What is the difference between a catch basin and a manhole?+
A catch basin collects surface water through an open grate and holds a sump below its outlet pipe to trap sediment. A manhole is an access structure with a solid cover, placed so crews can enter the pipe network for inspection and maintenance, and it does not take surface flow. They are counted the same way in a takeoff, each by depth class, but they carry different castings, details, and unit prices.
How is catch basin depth measured for estimating?+
Subtract the lowest invert elevation from the rim elevation shown on the utility plan or structure schedule, then add the sump depth from the project detail. That total vertical dimension determines how many precast sections the structure needs and how much trench excavation and backfill it carries. Estimators group the results into depth classes, commonly 2 ft steps, because that is how precast suppliers and utility subs quote.
What is included in the installed price of a catch basin?+
Typically the structure excavation, bedding, the precast base and riser sections, grade rings, the frame and grate, backfill, and final adjustment to grade after paving. The connecting storm pipe is not included; it is a separate lf takeoff. Watch the frame and grate spec closely, because a traffic rated curb inlet casting prices very differently than a pedestrian flat grate, even on structures with identical depth.
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Figures on this page are illustrative. Construction estimates depend on project-specific conditions, source documents, market pricing, and professional judgment. Ruh's AI assists the estimator and does not replace professional review: your team reviews, validates, and approves every estimate, bid, and pricing decision.