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Phase 1 · Site facts · Step 1.2

Geotech report if landslide / steep slope flagged

If Portland Maps flags a hazard or your lot slopes ≥25%, you need a geotechnical investigation. This isn't optional on flagged lots.

Who
Homeowner, Geotech eng.
How long
3-5 weeks
Cost
$3,500-$7,500
You end up with
Stamped geotechnical report

If you skip this: On landslide-hazard or steep-slope lots the geotech recommendation drives the foundation type. Discovering pile-required soils at excavation usually means weeks of redesign and a material change-order.

When you need this

Geotech is on the list if any of these are true:

  1. Portland Maps shows a landslide hazard. The hazard layer (Title 24.50) flags lots with documented landslide risk.
  2. Slope exceeds 25% anywhere on or near your proposed footprint.
  3. Environmental overlay (e/p/c) on the parcel — these usually imply geotechnical sensitivity.
  4. Title 33.430 review is triggered (environmental overlays in the west hills, riparian areas).

If none of those apply, skip this step.

What you get back

  • Soil borings (typically 2-3 for a DADU footprint)
  • Bearing capacity values your structural engineer needs to size footings
  • Foundation-type recommendation (slab, stem wall, deepened footing, pier)
  • Drainage and erosion-control recommendations
  • A clear statement on whether the site is safe to build on as proposed

How to choose one

  • Licensed by the Oregon State Board of Examiners for Engineering and Land Surveying.
  • Has done residential ADU work in the west hills, Mt Tabor, or wherever your slope is — they'll know what each PP&D reviewer wants.
  • Will deliver in time for your structural engineer's milestone. A geotech report that shows up after framing drawings are done is no help.

Where this information came from

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