Quick answer
You usually need a grading and drainage plan for new homes, larger additions, new driveways or pavement, work on slopes, and any project that moves significant soil or changes how water flows. The plan shows existing and proposed ground elevations, finished floor elevations, drainage paths, swales and downspout routes, any stormwater management, and erosion control during construction.
Water problems are among the most common neighbor complaints and building failures. A grading and drainage plan proves your project moves water away from buildings without sending it onto someone else’s property.
When a permit asks for one
- New homes and ADUs, especially on sloped or low lots
- Additions, pools or pavement that add impervious area
- Cut or fill beyond your jurisdiction’s grading threshold
- Retaining walls and terraced yards
- Sites in flood zones or near creeks and wetlands
What the plan shows
- Existing and proposed contours and spot elevations
- Finished floor and garage elevations
- Ground sloping away from the building on all sides
- Swales, drains, downspout connections and discharge points
- Stormwater retention or detention where required
- Erosion and sediment control: silt fence, inlet protection, construction entrance
Stormwater rules
Many jurisdictions require stormwater management when new impervious area exceeds a set amount, often through on-site retention, infiltration or detention. Construction sites disturbing one acre or more generally need coverage under the federal or state construction stormwater permit, with an erosion control plan.
Common mistakes
- Downspouts discharging next to foundations or onto neighbors
- Flat or reverse slopes near the house
- Fill placed against foundations or over property lines
- No plan for where water goes during heavy storms
What to send us
- Survey or topographic survey
- Site plan showing the new work
- Photos of the site and any drainage problems
- Property address
Get a fixed-fee quote. See civil engineering and site plans.
Common questions
Do I need a topographic survey for a grading plan?
Usually yes, because the plan is built from existing ground elevations.
Can I drain water onto my neighbor’s property?
You generally cannot increase or concentrate flow onto neighbors. The plan should keep water on your site or route it to an approved outlet.
Who prepares a grading and drainage plan?
A licensed civil engineer in most jurisdictions, especially when stormwater calculations are needed.
What is the difference between retention and detention?
Retention holds water to soak in or evaporate; detention stores it temporarily and releases it slowly.