How to Document Pad Elevation for Certification

Equipment You Need

For residential pad elevation surveys, you need either a total station or RTK GPS rover, the approved grading plan, and a copy of the local building department's pad certification requirements. GPS rovers are faster for open subdivisions (20-30 shots per hour vs 5-10 with a total station) but lose accuracy under tree canopy or adjacent structures. Total stations work anywhere.

You also need the approved grading plan — the version stamped and approved by the city or county. Design elevations must come from the current approved revision. Using a superseded plan version is a common rejection trigger.

Step 1: Set Up on a Known Benchmark

Before shooting a single lot, verify your instrument reads correctly against a known benchmark. Find the permanent benchmark referenced in the approved grading plan — typically a survey monument, BM nail set in concrete, or established control point. Set up your instrument and verify it reads the correct elevation before starting.

Document your benchmark: ID, elevation, datum (project datum as shown on the grading plan), and the date you verified it. This documentation becomes part of the PE package. A 0.03-foot error in your benchmark setup propagates to every shot on every lot.

Step 2: Shoot Lot Corner Elevations

Shoot a minimum of 5 points per lot: front left corner, front right corner, center of lot, rear left corner, rear right corner. On larger lots (over 7,500 SF) add midpoints on the long sides. For lots with swales or complex drainage, add shots along swale centerlines at the low point.

Record each shot against the corresponding design elevation from the approved grading plan. Calculate deviation: as-graded elevation minus design elevation. A positive deviation means the lot is high; negative means low. Flag any lot with a deviation greater than ±0.10 ft (or the applicable local tolerance).

Step 3: Verify Positive Drainage

Per IRC R401.3, the ground must slope away from the foundation at a minimum of 6 inches in the first 10 horizontal feet (approximately 5% slope), then 2% minimum to the lot line or drainage facility. This applies to all sides of the structure.

To verify: shoot elevations at the foundation corner, then at 2-foot intervals extending away from the structure to 10 feet, then at the lot line. Calculate slope at each interval. Any flat spot or reverse slope (drainage back toward the foundation) is a drainage failure — more common than you'd expect, usually from compaction-induced low spots adjacent to the foundation.

Step 4: Flag Failures and Re-Grade

Any lot outside tolerance or with drainage problems goes back to the grading contractor immediately. Document the specific failure: lot number, shot location, design elevation, as-graded elevation, deviation, and the nature of the failure (over-tolerance, drainage failure, or both).

After re-grading, re-shoot only the failed lots. You do not need to re-survey the entire subdivision. Document both the original failure shots and the corrected shots. The PE package must show the failure, the corrective action, and the final verified elevation.

Step 5: Compile the PE Package

Organize all data by lot number. The PE package must include: benchmark documentation (benchmark ID, elevation, datum, verification date), reference to the approved grading plan (plan number and approval date), a complete deviation summary table (lot number, shot location, design elevation, as-graded elevation, deviation, pass/fail for all lots), a drainage compliance statement, and corrective action documentation for any lots that required re-grading.

Submit to the PE of record for review and certification. Traditional workflow with paper field notes and spreadsheets takes 3-5 days for 50 lots. Digital workflow with real-time field data capture can produce the same package same day.

Common Mistakes

• Wrong grading plan version — Always confirm you have the current approved revision.
• Missing drainage documentation — Most building departments require drainage compliance, not just pad elevation. Don't skip the drainage slope verification.
• Not documenting corrective actions — When a lot fails and gets re-graded, both the original failure and the correction must be in the package.
• GPS under obstruction — GPS loses accuracy under tree canopy. Know when to switch to a total station.