Addition Structural Design in the West Hills, Portland
Building an addition on a West Hills lot is as much a permitting problem as a structural one, and the permitting problem should be understood before the design work starts. Sites on the mapped landslide hazard inventory attract additional review, and that review commonly requires a geotechnical report the structural design then has to be built on top of.
Getting that order wrong is the expensive mistake. A structural design produced first, then handed a geotechnical report specifying deeper foundations or a limit on added load near the slope, gets redrawn. Establishing what the ground can accept comes before deciding what to put on it.
The structural work itself is then mostly about reaching competent bearing and about keeping the addition from adding load where it is least welcome. On a steep lot that usually means a stepped or piered foundation carried well below the surface soils, and it frequently means keeping the new footprint away from the downhill edge even where the site technically allows it.
What We Look At Here
- Landslide hazard mapping status and what review it triggers, established first
- Whether a geotechnical report is required, and designing to its recommendations
- Foundation depth needed to reach competent bearing below surface soils
- Added load position relative to the slope, and whether it can be kept off the downhill edge
- Connection between new and existing foundations on stepped or uneven ground
- Drainage design, since the addition changes where surface water goes on a slope
More on the service itself: Addition & Remodel Structural Design. More on the area: West Hills.
Questions
Frequently Asked Questions
Do I need a geotechnical report for a West Hills addition?
Often, if the site is on the mapped landslide hazard inventory. It is worth establishing that before the structural design, because geotechnical recommendations govern foundation depth and load placement and will otherwise force a redesign.