Storm Sewer
Underground pipe, inlets and manholes that carry rainwater off a site.
Quick Answer
A storm sewer is the underground drainage system of pipe, inlets, manholes and outfalls that collects surface runoff and carries it away from a site, separate from sanitary sewer. In a takeoff, pipe is counted in linear feet by size and material, structures in each, and trench excavation and bedding in cubic yards.
The Full Picture
A storm sewer collects runoff from inlets, catch basins and area drains and moves it by gravity through pipe to a detention basin, a public storm main or an outfall. It is separate from the sanitary sewer, which carries wastewater. Because it relies on gravity, the pipe has to hold a slope, and that slope is what drives the excavation depth and therefore most of the cost.
Where it shows up in the documents: the civil set carries a storm drainage plan, profile sheets showing rim and invert elevations for every structure, a structure schedule, and details for bedding, manholes and inlets. The specifications for earthwork and for storm drainage piping (Division 31 and Division 33) cover pipe material, joints, bedding, backfill and testing. The geotechnical report matters too, since groundwater and rock change how the trench is priced.
How it is quantified: pipe is measured in linear feet by diameter and material, usually center of structure to center of structure, then reduced by the structure width so the same footage is not paid as both pipe and manhole. Inlets, manholes, headwalls, cleanouts and flared end sections are counted each. Trench excavation, bedding and backfill are cubic yards, driven by the invert depth at each end of a run rather than a single average depth for the job. Pavement cut, restoration and dewatering are carried as separate lines.
The usual pricing mistakes are depth-related. An estimator who prices every run at the depth of the first manhole will undercount excavation on the deep runs, and one who forgets that the dig is deeper than the invert (pipe wall plus bedding) is short on every run. Others miss that rim elevations are set by finished grade, so a structure that looks shallow on the plan may be deep once grading changes. Trenches deeper than 5 feet generally need a protective system under OSHA's excavation rules, which changes the width and quantity carried. On sites that disturb an acre or more, runoff controls are also regulated under EPA's construction general permit, so inlet protection often becomes its own line.
Real Examples
Common Misconceptions
People assume: Storm sewer is just pipe, so footage times a unit price covers it.
Actually: Structures, excavation by depth, bedding, backfill, pavement restoration, dewatering and testing are all separate quantities. Pipe footage alone often understates the scope by a large share of the cost.
People assume: Storm sewer and sanitary sewer are interchangeable in the estimate.
Actually: They are separate systems with different pipe materials, structures, testing and approval agencies. A civil set often prices them under different spec sections and sometimes different subcontractors.
People assume: The invert elevation is the bottom of the trench.
Actually: The invert is the inside bottom of the pipe. The trench bottom is lower by the pipe wall and bedding thickness, so quantities taken at invert depth come up short.
Does MeltPlan Solve This?
Partially — adjacentStorm sewer is a physical scope an estimator counts and measures from civil plans. MeltPlan's takeoff uses AI to pull quantities from PDF plans, and US-based experienced estimators review and adjust them so the output is a verified, ready-to-use takeoff. Design of the drainage system itself stays with the civil engineer.
Get pipe and structure counts from civil plans →Frequently Asked Questions
How is storm sewer measured in a takeoff?
Pipe is measured in linear feet by diameter and material, structures such as manholes and inlets are counted each, and trench excavation, bedding and backfill are measured in cubic yards. Pavement cutting and restoration are usually separate square yard or linear foot items.
What is invert depth and why does it matter?
Invert depth is the depth from finished grade (the rim) down to the inside bottom of the pipe at a structure. It sets how deep the trench must be at each end of a run, which drives excavation volume, shoring needs and the number of days the crew spends on the run.
Where do I find storm sewer information in the plan set?
Look at the civil drainage plan, the profile sheets with rim and invert elevations, the structure schedule and the standard details. Pipe and bedding requirements are in the civil specifications, typically under Division 31 for earthwork and Division 33 for utilities.
Does the pipe LF include the manholes?
It depends on how the measurement is written. Many estimators measure center to center and subtract the structure width, so the footage is not counted twice. Check the spec's measurement and payment language and stay consistent across runs.
What is the difference between storm sewer and storm drain?
In everyday use the terms overlap. Storm drain often refers to the inlet and the building or roof drain connections, while storm sewer usually means the main underground pipe network those connections discharge into.