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Phase 1 · Site and existing conditions · Step 1.4

Order a geotech report if the lot is on a slope or in an e-zone

Lots in environmental overlays, on slopes >15%, or with known landslide hazards need a geotechnical engineer's site investigation before design. Flat inner-east-side lots usually don't.

Who
Geotech eng.
How long
3-5 weeks
Cost
$2,500-$6,000
You end up with
Stamped geotechnical report with bearing capacity and slope-stability recommendations

When you need a geotech

You need a geotech report when one of these is true:

  • The lot is in an Environmental Conservation (c) or Environmental Protection (p) overlay.
  • The lot has a landslide hazard layer on Portland Maps.
  • The lot has any natural slope greater than ~15%.
  • The structural engineer's foundation assessment said the soil-bearing assumption needs verification.

If none of those apply — flat lot, no overlays, sound soil — you can skip the geotech and the structural engineer can use the conservative default soil-bearing values from the ORSC.

What the geotech does

A licensed Oregon geotechnical engineer:

  1. Reviews regional geology and any existing reports for the area.
  2. Mounts a small drill rig (or hand augers) and takes 1–3 borings on your lot, typically 15–25 ft deep.
  3. Logs soil layers, groundwater depth, and shear strength.
  4. Writes a stamped report with foundation recommendations: allowable bearing pressure, recommended footing depth, lateral earth pressures, and slope-stability conclusions.

Why this matters now

For a second-story addition, the additional dead load on the existing foundation is real but moderate (typically 10–25% of total). What matters more is whether the soil under the existing foundation can carry that increase without settlement. The geotech answers that question.

For lots in environmental zones or with landslide hazards, the geotech report is also a permit submittal requirement — without it, PP&D won't intake the application.

What good looks like

A 15–25 page report with:

  • Site map showing boring locations.
  • Soil profile logs.
  • Allowable bearing pressure (psf).
  • Foundation type recommendation (continuous spread footing, shallow piers, deep piers if soil is poor).
  • Slope-stability discussion (if applicable).
  • Construction recommendations (drainage, backfill, vapor barrier).

The structural engineer uses these numbers directly in the foundation design. PP&D wants the report attached to the submittal as a separate PDF.

Where this information came from

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