A practical guide to interpreting grading and drainage plans on construction documents

Grading plans define how the land will be shaped to direct surface water away from buildings, create usable site areas, and connect to the public drainage system. They are typically part of the civil (C-series) drawing set and are among the most critical sheets for site construction. Errors in grading can cause flooding, structural damage, ADA non-compliance, and costly rework.

Step 1: Understand Existing vs. Proposed Grades

Grading plans show two layers of information: the existing topography (from the survey) and the proposed design grades. Being able to distinguish between them is the first skill to master.

Existing Grades

Shown as dashed or lightweight contour lines and spot elevations. Based on the topographic survey. Often printed in a lighter color or thinner line weight.

Proposed Grades

Shown as solid, bold contour lines and spot elevations. Represent the finished design after earthwork is complete. These are what the contractor builds to.

Cut and Fill

Where proposed contours are higher than existing = fill (importing soil). Where proposed contours are lower than existing = cut (excavating soil). The difference determines earthwork quantities.

Step 2: Read Contour Lines and Spot Elevations

Contour lines and spot elevations work together to define the three-dimensional shape of the ground. Contour lines show broad patterns; spot elevations provide precise points.

Contour Interval

The vertical distance between adjacent contour lines. Typically 1' for site grading plans. Index contours (every 5th line) are drawn heavier and labeled.

Reading Direction of Slope

Water flows perpendicular to contour lines, from higher elevations to lower. If contours read 102, 101, 100 from left to right, water flows left to right.

Spot Elevations

Precise elevations marked at critical locations: building corners, curb tops, flow lines, high/low points, and grade breaks. These control construction grading.

Dual Elevations

Some plans show both existing and proposed elevations at the same point: "EX 100.5 / PR 101.2" means the ground is being raised 0.7 feet at that location.

Slope Calculation: Slope % = (Rise ÷ Run) × 100. Between two spot elevations of 101.0' and 100.0' that are 50' apart: (1.0 ÷ 50) × 100 = 2.0% slope. Minimum 1% for paved surfaces, 2% recommended for positive drainage.

Step 3: Follow Drainage Arrows

Drainage arrows (flow arrows) show the intended direction of surface water flow. They are typically triangular arrows with the slope percentage noted alongside. These connect to the stormwater management plan for downstream conveyance.

Verify that all drainage arrows point away from building perimeters — minimum 5% slope within 10 feet of foundations

Check that parking areas drain toward catch basins, not toward building entries or adjacent properties

Confirm that swales (shallow channels) have adequate slope to convey water — minimum 1% for grass, 0.5% for paved

Look for drainage divides (high points) — these determine which drainage basin each area belongs to

Verify that no drainage arrows direct water toward neighboring properties without proper easements

Check that accessible routes do not cross drainage swales or areas where water may pond

Step 4: Check Building Pad Elevations

The building pad elevation (Finished Floor Elevation, or FFE) is one of the most critical numbers on the grading plan. It determines the relationship between the building interior and the surrounding site. Cross-reference this with the architectural drawings to confirm consistency.

FFE vs. Grade Relationship

The FFE should be a minimum of 6-8 inches above adjacent finish grade to prevent water entry. More in flood-prone areas.

Cross-Reference with Architectural

Verify that the civil FFE matches the architectural floor plan FFE. Discrepancies are a common coordination error.

Garage/Loading Dock

Depressed areas (garages, loading docks) must have trench drains or area drains to prevent flooding, with drain connected to storm system.

Entry Transitions

Grade at entries must slope away from doors while maintaining ADA-compliant slopes. The transition from site grade to FFE often requires careful detailing.

Step 5: Verify ADA Accessible Routes

All pedestrian routes from accessible parking, public rights-of-way, and transit stops to building entries must comply with ADA/ABA Accessibility Guidelines. Refer to our ADA accessibility guide for the full set of requirements.

Running Slope

5.0% maximum (1:20)

Slopes exceeding 5% are classified as ramps

Cross Slope

2.0% maximum (1:50)

Perpendicular to direction of travel

Ramp Slope

8.33% maximum (1:12)

30" max rise per run, landings at top and bottom

Accessible Parking Slope

2.0% maximum in any direction

Applies to stall and access aisle

Step 6: Review Retaining Wall Locations

Where grade changes exceed what can be achieved with slopes alone, retaining walls are required. Look for these indicators on the grading plan:

Retaining walls shown as heavy lines with TW (Top of Wall) and BW (Bottom of Wall) elevations

Walls over 4 feet in exposed height typically require structural engineering design

Check for drainage behind walls — retaining walls need weep holes or drainage aggregate and pipe

Verify adequate setback from property lines — retaining walls and their foundations may encroach

Look for surcharge conditions — parking, roadways, or buildings above the wall increase lateral pressure

Confirm wall type is specified: gravity, cantilever, mechanically stabilized earth (MSE), or segmental

Common Grading Plan Symbols

╌╌╌Existing Contour

Dashed or light lines showing current ground elevation

───Proposed Contour

Solid or bold lines showing designed finish grade

⊗ 100.50Existing Spot Elevation

Surveyed elevation at a specific point

⊕ 101.25Proposed Spot Elevation

Designed finish grade at a specific point

TC 101.5Top of Curb

Elevation at the top of curb

FL 100.8Flow Line

Elevation at the gutter or drainage channel bottom

HP 102.0High Point

Local high point for drainage divide

LP 99.5Low Point

Local low point where water collects

FFE 102.50Finished Floor Elevation

Building entry or floor slab elevation

▶ 2.0%Slope Arrow

Direction and percentage of surface drainage

TW / BWTop/Bottom of Wall

Retaining wall top and bottom elevations

INV 98.25Invert Elevation

Bottom inside elevation of a pipe

Related Resources

How to Read Civil Drawings

Complete civil drawing reading guide.

How to Read a Site Plan

Site layout and overall plan interpretation.

Roof Drainage Design

How roof drainage connects to site grading.

Waterproofing Failures in Construction

How poor grading contributes to water intrusion.

AI Accessibility Checking

Automatically verify ADA slope compliance on grading plans.

Solutions for Civil Engineers

How Articulate supports civil engineering review workflows.

Automate Grading Plan Review

Articulate's AI can analyze grading plans to verify positive drainage away from buildings, check ADA slope compliance, and flag inconsistencies between civil and architectural FFE values.

Try Automated Drawing Review

Sources

ADA/ABA Accessibility Guidelines (ADAAG) — Chapter 4: Accessible Routes

IBC 2021, Section 1804 — Excavation, Grading, and Fill

ASCE 7-22 — Flood Loads

How to Read a Grading Plan