Quick answer: Choose a civil engineer who is registered in Georgia and works through a firm with a Georgia Certificate of Authorization, holds GSWCC Level II certification for erosion control plans, has permitted ADU or single-lot grading work in your city or county, designs grading and stormwater in-house, and gives you a written scope and timeline. Those five checks are verifiable before you sign.
Last updated: October 2026
An accessory dwelling unit (ADU) looks like a small building project, but in Georgia the site work is often what holds up the permit. Grading, drainage, erosion control, state-water buffers and septic capacity are reviewed by different offices, and each Georgia county and city applies its own rules on top of state law. This guide covers what a civil engineer does on a Georgia ADU, when a grading or land disturbance permit is triggered, how to vet an engineer, and how long review takes under the 2026 permit-deadline law.
In this guide
- What does a civil engineer do on a Georgia ADU project?
- When does a Georgia ADU need a grading or erosion control permit?
- What five things should you check before hiring?
- What local review issues slow Georgia ADU permits?
- How do you keep ADU runoff off your neighbor’s property?
- What drives the cost of ADU civil engineering in Georgia?
- How long does grading and land disturbance review take in Georgia?
- How does Mack Engineering handle ADU and grading plans in Georgia?
- What mistakes should you avoid?
- Frequently asked questions
- Key takeaways
- Sources
What does a civil engineer do on a Georgia ADU project?
On a Georgia ADU, the civil engineer designs everything outside the building footprint: where the unit sits, how the ground is shaped around it, where water goes, and how utilities reach it. The core deliverables are a site and utility plan, a grading and drainage plan, and, when required, an erosion, sedimentation and pollution control (ES&PC) plan and stormwater calculations.
Georgia rules define land disturbing activity broadly, including clearing, dredging, grading, excavating, transporting and filling of land (Georgia Rules 391-3-7). That is why even a modest backyard pad, driveway extension or utility trench can fall under review.
Typical civil scope for a Georgia ADU
- Boundary and topographic survey coordination (performed by a Georgia land surveyor; see civil engineer vs. land surveyor)
- Site layout showing setbacks, lot coverage and the ADU footprint for zoning review
- Grading plan with existing and proposed contours, finished floor and pad elevations, and spot grades
- Drainage design: swales, downspout discharge, inlets or pipes, and any infiltration or detention practice
- Erosion and sediment control plan (silt fence, construction exit, inlet protection, stabilization)
- Water, sewer or septic routing, coordinated with the utility provider or county Environmental Health
- Retaining wall layout and grading, with wall structural design coordinated separately
Civil work is not structural work. Foundation design and framing loads for the ADU itself belong to a structural engineer; see structural vs. civil engineer in Georgia.
Under Georgia sealing rules, each final drawing sheet must carry the seal, signature and date of the responsible registrant plus the firm’s Certificate of Authorization name, number and expiration date, and sealing certifies the work was done by or under the direct supervision of that registrant (Georgia Rule 180-12).
When does a Georgia ADU need a grading or erosion control permit?
It depends on disturbed area, distance to streams, whether the lot is in a newer subdivision, and the local ordinance. State law sets the floor, and Georgia counties and cities are allowed to be stricter.
The state exemption for projects disturbing less than one acre does not apply inside a common development planned for one acre or more, or within 200 feet of the banks of perennial state waters; work within that 200-foot zone must meet state minimum requirements and needs a land disturbing activity permit from the local issuing authority (Georgia EPD).
| Site condition | What it typically triggers | Georgia source |
|---|---|---|
| Disturbance of 1 acre or more | Land disturbance permit (LDP) plus NPDES construction stormwater coverage | Dawson County |
| Any disturbance within 200 ft of perennial state waters | LDP and an ES&PC plan by a GSWCC Level II certified design professional, regardless of size | Georgia EPD; Athens-Clarke County |
| Lot in a subdivision platted or recorded after January 1, 2000 | Often an LDP even under 1 acre, because newer subdivisions carry post-construction stormwater rules | Dawson County |
| Stream on or next to the lot | 25-ft undisturbed state buffer on warm-water streams, 50-ft on designated trout waters; variance needed to encroach | GDOT buffer guidance |
| Local buffer ordinance | Additional county buffers, such as DeKalb’s 75-ft county buffer | DeKalb County |
| Under 1 acre, no state waters, older lot | Still regulated locally: Cherokee issues an Erosion Control Permit under 1 acre; Athens-Clarke requires a single-phase ES&PC sheet for all disturbance | Cherokee County; Athens-Clarke County |
A flat-looking lot is not automatically exempt. Changing where water drains, adding impervious area, or placing fill near a property line can each pull the project into grading, stormwater or erosion review. Confirm the requirement with the local planning or development office before design starts; Mack’s land disturbance permit cost and timeline guide and Cherokee County LDP guide cover local specifics.
What five things should you check before hiring?
Use these five checks. Each one can be verified with a public record or a document the engineer should be able to hand you.
| Check | Why it matters in Georgia | How to verify |
|---|---|---|
| 1. Georgia PE license and firm COA | Any business entity offering engineering in Georgia must hold a Certificate of Authorization; sole proprietors are the only exception | Search the Georgia PE/LS license database; see COA rules. Check the COA number on the plan sheets. |
| 2. GSWCC Level II certification | Required for ES&PC plans; Hall County will not review a plan unless the Level II number, signature and seal appear on each ES&PC sheet | Ask for the Level II number. Eligibility requires Georgia licensure in engineering or a related field (GSWCC); see Hall County checklist. |
| 3. ADU and single-lot experience in your jurisdiction | Single-lot review issues (septic, buffers, neighbor drainage) differ from subdivision work, and each county reads its code differently | Ask for 2 to 3 permitted ADU, addition or single-lot grading projects in your city or county, with the permit number if possible. |
| 4. In-house grading, stormwater and utility design | Stormwater is reviewed against the Georgia Stormwater Management Manual or a local equivalent; septic goes to county Environmental Health | Ask who prepares the drainage calculations and who coordinates Environmental Health. One firm owning both reduces conflicting revisions. |
| 5. Written scope, deliverables and timeline | Georgia now has statutory LDP review deadlines; your engineer should plan around them and respond to comments quickly | Get a written list of sheets, survey needs, resubmittal rounds included, and target submittal date before signing. |
What local review issues slow Georgia ADU permits?
The most common delays on Georgia ADUs come from four places: local ADU zoning, septic capacity, stormwater standards and floodplain status. A local engineer should identify all four in the first site review.
ADU zoning is set locally
Georgia had no statewide ADU law in force as of 2026, so each city and county decides whether ADUs are allowed and at what size (ADU Zoning, Georgia). Confirm the district, size, height and setback limits with the local planning department before design. Mack’s ADU Permits in Georgia guide covers more jurisdictions.
Septic capacity
Georgia Department of Public Health rules size residential septic tanks by bedroom count (1,000 gallons for one to four bedrooms, plus 250 gallons for each additional bedroom) and require repairs, replacements or additions to be permitted and inspected (Georgia DPH Chapter 511-3-1). An ADU that adds bedrooms usually needs an existing system evaluation; one district lists a $125 residential evaluation fee and notes that required modifications may need a Level 3 soil report or site plan (Northeast Health District). Grading or filling after a septic permit is issued may void that permit (Southeast Health District), so grading and septic layout must be designed together. See Mack’s septic design and Level 3 soil report guide.
Stormwater standards
Georgia jurisdictions covered by a municipal stormwater (MS4) permit are required to use the 2016 Georgia Stormwater Management Manual, known as the Blue Book, or an equivalent manual (Atlanta Regional Commission). Local thresholds for when a single lot needs stormwater management vary; Mack’s Forsyth County stormwater requirements page is one local example.
Floodplain status
Check the lot on the FEMA Flood Map Service Center before design (FEMA, Georgia). Local rules can be stricter than federal minimums: Gwinnett County’s ordinance prohibits construction within the floodplain and requires a home built on a floodplain lot to be elevated three feet above the base flood elevation (Gwinnett County).
Utility locates
Georgia law requires contacting Georgia 811 before mechanized digging, at least three business days and no more than 10 working days in advance (Georgia 811). Build that into the construction schedule for utility trenches and footings.
How do you keep ADU runoff off your neighbor’s property?
Keep water on your lot by designing where it goes before construction starts. A grading plan sets finished grades so runoff moves away from the ADU and toward a controlled discharge point on your property, not across the property line.
- Slope finished grade away from the ADU foundation and the main house
- Route roof downspouts to a splash pad, dry well, rain garden or other approved outlet set back from the property line
- Use shallow swales to carry runoff along, not toward, the shared lot line
- Show existing drainage paths from neighboring lots so new fill does not block water that already crosses your property
- Place silt fence and a construction exit before grading, and stabilize bare soil quickly
Georgia ES&PC plans must state that the escape of sediment from the site shall be prevented by installing erosion and sediment controls before or concurrent with land disturbance (DeKalb County checklist). Cherokee County describes its land disturbance rules as protecting water quality and neighboring properties (Cherokee County). For existing drainage problems, see Mack’s backyard drainage ditch guide.
What drives the cost of ADU civil engineering in Georgia?
Civil engineering cost for a Georgia ADU depends mostly on site conditions, not building size. The main drivers are:
- Whether a new boundary and topographic survey is needed
- Slope, retaining walls and the volume of cut and fill
- Distance to streams, ponds or wetlands (the 200-foot state-water trigger)
- Septic versus public sewer, and whether a soil report is required
- Whether the lot is in a post-2000 subdivision with stormwater obligations
- Number of review comment rounds included in the scope
Some government fees are fixed. When disturbance reaches one acre, NPDES construction permit fees in DeKalb County are $40 per disturbed acre to the county and $40 per disturbed acre to Georgia EPD (DeKalb County). Septic evaluations carry separate health-district fees, as noted above.
A plan set that is rejected costs more than one done right the first time, because redesign and resubmittal fees stack on top of schedule delay. Ask for a fixed scope with stated resubmittal rounds instead of open-ended hourly billing. Mack’s civil engineer cost guide for Metro Atlanta breaks down typical fee structures.
How long does grading and land disturbance review take in Georgia?
For land disturbance permits, Georgia now has statutory deadlines. Senate Bill 447, effective July 1, 2026, gives the local issuing authority 5 days to determine whether an application is complete, 45 days to issue or deny an initial application, 20 days after the first resubmission, and 14 days after later resubmissions; new comments generally must relate to the original comments or the applicant’s revisions (Nelson Mullins). A missed deadline means a fee refund and possible mandamus relief, not automatic approval. The local review clock pauses while a required state-agency review is underway (CPL). Mack’s SB 447 guide explains the details, and our guide to avoiding land disturbance permit delays covers how to keep a submittal from bouncing.
Some counties route the ES&PC plan to the Georgia Soil and Water Conservation Commission first. Dawson County, for example, requires the plan to be reviewed and stamped by GSWCC in Athens before the LDP application is submitted (Dawson County). The ADU building permit is a separate review with its own local timeline.
Typical Georgia sequence
- Zoning and feasibility check (ADU allowed? setbacks, coverage, buffers, floodplain, septic or sewer)
- Boundary and topographic survey
- Concept site plan coordinated with the architect
- Grading, drainage, utility and ES&PC design
- Environmental Health septic evaluation or utility approvals, if needed
- Submittal to the local issuing authority (and GSWCC, where required)
- Comment response and resubmittal
- Permit issuance, Georgia 811 locates, then construction
Bring the civil engineer in while the architect is still in concept design, not after. Site limits such as a buffer or septic field can move the ADU footprint, and finding that late forces architectural redesign.
How does Mack Engineering handle ADU and grading plans in Georgia?
Mack Engineering is a Georgia civil engineering and land development firm based in Alpharetta that works for property owners, builders and developers. ADU site and grading scopes are handled in-house with stormwater, erosion control, septic and sewer design, so one team coordinates the full civil plan set.
- Feasibility reports and concept site plans to confirm an ADU fits the lot before design money is spent
- Zoning exhibits and land disturbance plans documenting setbacks, coverage and disturbance limits
- Grading plans, sanitary sewer and septic designs, erosion and sediment control, and ADU site engineering
- Stormwater design and hydrology studies for drainage, detention and water quality requirements
- Construction management and builder services to keep the design intent intact in the field
Mack works across Georgia, with project history in Metro Atlanta and North Georgia communities including Milton, Canton and Cumming; see areas we serve.
Ready to check whether an ADU works on your lot? Contact Mack Engineering or call (770) 715-7295. Office: 5745 Stables Wy A-09, Alpharetta, GA 30004.
What mistakes should you avoid?
- Hiring after architecture is finished. Buffers, septic fields and grade changes can move the footprint.
- Assuming a small or flat lot is exempt. The 200-foot state-water rule applies at any size, and many Georgia jurisdictions regulate disturbance under one acre.
- Ignoring the septic system. Grading over or near the drain field can void the septic permit and kill the project.
- Skipping the flood map. Floodplain lots can face elevation requirements or construction limits.
- Not planning for neighbor drainage. Water pushed across a property line is a common source of complaints and enforcement.
- Choosing on price alone. Confirm the Georgia PE license, firm COA and GSWCC Level II number before you sign.
Frequently asked questions
Often, yes. Georgia law requires a local permit and an erosion, sedimentation and pollution control (ES&PC) plan by a GSWCC Level II certified design professional for any land disturbance within 200 feet of perennial state waters, regardless of size. Counties and cities can add stricter rules; Athens-Clarke requires an ES&PC sheet for all disturbance, and Cherokee issues an Erosion Control Permit for clearing and grading under one acre.
Engineering drawings must be sealed by a Georgia-registered professional engineer, and a firm offering engineering must hold a Certificate of Authorization from the Georgia Professional Engineers and Land Surveyors Board. Where an ES&PC plan is required, the preparer must also hold GSWCC Level II certification and list that number on the plan sheets.
Under Senate Bill 447, effective July 1, 2026, a local issuing authority has 5 days to determine completeness and 45 days to issue or deny an initial land disturbance permit, then 20 days after the first resubmission and 14 days after later resubmissions. ADU building permit review is a separate process with its own local timeline.
Possibly, but the county Environmental Health office must approve it. Georgia Department of Public Health rules size septic tanks by bedroom count and require additions to be permitted, so an ADU that adds bedrooms usually triggers an existing system evaluation and sometimes a Level 3 soil report.
No statewide ADU law was in force as of October 2026. Each city or county sets its own ADU zoning rules, so district, size, height and setback limits must be confirmed with the local planning department before design.
Have a civil engineer set finished grades that direct water away from the structure and toward an approved discharge point on your lot, size swales, downspout outlets and any infiltration or detention practice, and show sediment controls. Georgia ES&PC plans must state that the escape of sediment from the site shall be prevented.
The civil engineer handles the site: grading, drainage, erosion control, utilities and stormwater. The structural engineer designs the foundation and framing loads of the ADU itself. Many Georgia ADU projects need both.
Key takeaways
- Georgia engineering drawings must be sealed by a Georgia PE, with the firm’s Certificate of Authorization on every sheet.
- Any land disturbance within 200 feet of perennial state waters needs a local permit and a GSWCC Level II ES&PC plan, regardless of size.
- Counties and cities can regulate disturbance under one acre; post-2000 subdivision lots often need an LDP.
- Septic capacity is set by bedroom count, and grading after a septic permit can void it.
- SB 447 sets a 45-day initial review deadline for land disturbance permits, with 20- and 14-day resubmittal deadlines, effective July 1, 2026.
- Georgia has no statewide ADU law in force; ADU zoning is local.
- Bring the civil engineer in during concept design, not after architecture.
Related reading
- ADU permits in Georgia: a guide by jurisdiction
- Georgia SB 447 and the 45-day land disturbance permit deadline
- How to avoid delays in land disturbance permit approval
- Septic system design in Georgia: Level 3 soil reports and site limits
- Structural vs. civil engineer in Georgia: which do you need?
- How much does a civil engineer cost in Metro Atlanta?
- Stormwater design and hydrology studies
Sources
- Georgia EPD, Erosion & Sedimentation Control Education and Certification Fact Sheet
- Georgia Rules and Regulations, Chapter 391-3-7, Erosion and Sedimentation Control
- Georgia Rules and Regulations, Chapter 180-12, Sealing of Documents
- Georgia Professional Engineers and Land Surveyors Board, PE/LS Business Entity (COA)
- Georgia Professional Engineers and Land Surveyors Board, Licensing Services and License Search
- Georgia Soil and Water Conservation Commission, Introduction to Design (Level II)
- Hall County, ES&PC Plan Guidance, Stand-Alone Construction Projects (GAR100001), 2026
- DeKalb County, Erosion and Sediment Control Plan Review Checklist
- Athens-Clarke County, ES&PC Plans for Single Family Homes: A Step-by-Step Guide
- Cherokee County, Development and Land Disturbance Permit
- Dawson County, How to Get a Land Disturbance Permit
- Georgia DOT, Buffer Variances Guidebook
- Atlanta Regional Commission, Georgia Stormwater Management Manual (2016)
- Georgia Department of Public Health, Rules Chapter 511-3-1, On-Site Sewage Management Systems
- Northeast Health District, Existing System Evaluation Request Form
- Southeast Health District, On-Site Sewage Application
- ADU Zoning, Georgia ADU Laws and Rules by City (2026)
- FEMA, Risk Reduction: Georgia
- Gwinnett County, Flood Information
- Georgia 811, Who We Are
- Nelson Mullins, 2026 Georgia Construction Legislation: Contractor Licensing, Permit Review, and Public Roofing
- CPL, Georgia Senate Bill 447 Permitting Compliance Whitepaper
This article is general information, not a site-specific engineering opinion. Code requirements and local ordinances change; confirm current requirements with the authority having jurisdiction for your property.