Order a soils or geotech report if conditions require it

When you need a soils or geotech report in Renton

You need one when any of these applies:

• The lot is in or within 500 feet of a high Coal Mine Hazard Area per RMC 4-3-050. Check your address on the Renton GIS Hub Coal Mine Hazard layer.
• A geologic hazard is present on-site or within 50 feet — seismic hazard, slope instability, or liquefaction. WA DNR has published a liquefaction susceptibility map for the Renton area (ger_gm41).
• The structural engineer's assessment said the soil-bearing assumption needs verification.
• The site has visible water issues — standing water, springs, prior settlement at the existing foundation.

If none of those apply — a standard flat Renton lot, no CMH overlay, sound existing foundation — you can skip the full geotech and the structural engineer uses conservative default bearing values.

What the report does

1. Confirms the allowable bearing pressure for the new addition foundation.
2. Recommends footing depth and any drainage details.
3. Identifies unusual conditions — fill, organic soil, perched groundwater, or proximity to former mine workings.

The Coal Mine Hazard overlay is the Renton-specific factor that doesn't have a direct Seattle equivalent. If you're in the CMH zone, Renton CED requires the geotech report and in some cases independent review of the findings at the applicant's expense.