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Project GuideResidential/Commercial

Building a Hillside Development?

Slope stability, retaining walls, and specialized foundations — what hillside projects require in Southern California.

Building on a Hillside Isn't Like Building on a Flat Lot

Hillside development in California requires specialized geotechnical and civil engineering. You're not just dealing with a foundation — you're dealing with slope stability, deeper borings, retaining wall design, complex drainage, and jurisdictions that have seen hillside projects fail when the engineering was inadequate.

The building department requires slope stability analysis to prove the hillside can support your structure. They require deeper geotechnical investigations to evaluate potential failure planes. They require drainage systems that won't destabilize the slope. And they require retaining walls designed by someone who understands lateral earth pressure and seismic loading.

We work on hillside projects across Southern California — from coastal bluffs in La Jolla to ridgeline sites in the Hollywood Hills. We know what these projects require, and we know how to navigate the specialized review processes that come with them.

What You'll Need

Engineering deliverables for hillside development projects:

Required

🪨

Slope Stability Analysis

Required for any building on slopes exceeding 25-33% (varies by jurisdiction). Computer modeling evaluates the hillside's stability under static and seismic loading and determines required safety factors.

Required

🔩

Soils Report (Deep Investigation)

Hillside sites require deeper borings — typically to bedrock or competent material. The investigation evaluates soil strength, groundwater, and potential failure planes that could affect the structure.

Usually Required

🧱

Retaining Wall Design

Most hillside projects require retaining walls to create level building pads. We provide geotechnical design parameters — lateral earth pressure, bearing capacity, drainage recommendations — that your structural engineer uses for wall design.

Required

📐

Grading Plan

Cut-and-fill grading on hillsides is complex. The plan shows excavation limits, fill placement, compaction zones, slope ratios, and drainage systems. Requires coordination with slope stability recommendations.

Usually Required

💧

Drainage & Subdrain Design

Hillside drainage is critical for slope stability. The design includes surface drainage, subsurface drains behind retaining walls, and sometimes deep drains to lower groundwater in the slope.

Required

🏗

Compaction & Observation

Hillside grading requires continuous observation and testing. We verify cut slopes are stable, fill is properly compacted, and retaining wall backfill meets specifications.

Why Hillside Projects Get Extra Scrutiny

Jurisdictions have seen hillside failures. Landslides, retaining wall collapses, homes damaged by slope movement — these aren't theoretical risks. Building departments in areas with significant hillside development (LA, San Diego, Orange County) have specialized review staff who scrutinize geotechnical reports and grading plans for hillside projects.

The extra engineering isn't bureaucratic overhead — it's the difference between a stable, insurable property and one that slides downhill during the next El Niño. We've worked on hillside projects where cutting corners on the geotech would have saved $10,000 upfront and cost $500,000 in landslide repairs later.

2:1

Typical slope ratio where specialized hillside engineering becomes required

1.5

Minimum factor of safety against slope failure required by most building codes

Hillside borings are typically 3x deeper than flat-lot investigations

What to Expect

Site Reconnaissance & Proposal

We visit the site, evaluate slope conditions, and research jurisdiction-specific hillside requirements. Proposal includes all anticipated deliverables.

Deep Geotechnical Investigation

We drill deeper borings to evaluate slope stability, often to bedrock. Laboratory testing characterizes soil strength and expansion potential.

Slope Stability Analysis

Computer modeling evaluates the hillside under various conditions — dry, saturated, seismic loading. Determines required stabilization measures if needed.

Engineering Plans & Coordination

We prepare the soils report, grading plan, and retaining wall geotechnical parameters. Everything coordinates — the grading follows slope stability recommendations.

Construction Observation

Hillside grading requires ongoing observation. We verify slope cuts, compaction, wall backfill, and drainage installation throughout construction.

Building Something Else?

ADU Engineering Guide

Engineering deliverables for ADU construction in California.

Read Guide →

Retaining Wall Engineering

When you need geotech for walls, and what's involved.

Read Guide →

Pool Engineering Guide

Pool soils reports and foundation engineering.

Read Guide →

Common Questions

Typically slopes steeper than 25-33% (varies by jurisdiction). Some agencies also trigger hillside requirements based on elevation change or proximity to slopes, even if the building pad itself is relatively flat.

Deep enough to evaluate potential failure planes — often 1.5-2x the slope height, and frequently to bedrock or very dense material. Hillside borings are significantly deeper than flat-lot investigations.

Technically, yes — but at what cost? Very steep or geologically weak slopes may require extensive stabilization: massive retaining walls, deep foundations, drainage systems, or buttress fills. At some point, the cost exceeds the property value.

Groundwater significantly reduces slope stability. The geotechnical report will typically recommend subdrain systems to lower the water table and improve the factor of safety.

Often, yes. Hillside projects face more detailed plan review, sometimes by specialized reviewers. Expect longer review times and more thorough corrections rounds.

Ready to Get Your Hillside Development Started?

Tell us about your hillside development project and we'll send a proposal with every deliverable you need — scope, fee, and timeline.

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