Updated: November 2025
Slab foundations are the most common foundation type in Ontario, California, and throughout the Inland Empire. When properly designed and constructed, they provide excellent performance for decades. As part of our foundation engineering services, AAA Engineering Design provides expert slab foundation engineering for Ontario properties in San Bernardino County.
What Is a Slab Foundation?
A slab foundation (also called slab-on-grade) is a concrete foundation that sits directly on the ground, serving as both the building's foundation and the floor. In Ontario's climate and soil conditions, slab foundations offer practical advantages for most residential and light commercial construction.
**Key Components:**
- Concrete slab (typically 4"-6" thick)
- Thickened edges (footings integrated into slab)
- Reinforcement (rebar or welded wire)
- Vapor barrier beneath slab
- Prepared subgrade
Types of Slab Foundations for Ontario Properties
Monolithic Slab **Single-Pour Construction**
The entire foundation—slab, edge beams, and interior footings—poured in one operation.
**Specifications:**
- Slab thickness: 4"-5"
- Edge beam: 12"-18" wide x 12"-18" deep
- Interior footings at bearing walls
- Reinforcement throughout
**Advantages:**
- Most economical
- Fast construction
- Fewer construction joints
- Works well on prepared sites
**Best For:**
- Level Ontario lots
- Standard residential construction
- Cost-conscious projects
**Cost:** $8-$12 per square foot
Stem Wall with Slab **Two-Stage Construction**
Separate footings and stem walls built first, then floor slab poured inside.
**Specifications:**
- Spread footings: 12"-24" wide
- Stem walls: 6"-8" thick
- Floor slab: 4" minimum
- Independent reinforcement systems
**Advantages:**
- Accommodates grade changes
- Creates crawl space option
- Better for sloped sites
- More adjustability
**Best For:**
- Ontario properties with grade changes
- Sites requiring crawl space
- Custom home designs
**Cost:** $14-$20 per square foot
Post-Tensioned Slab **High-Performance Foundation**
Steel cables tensioned after concrete cures create a rigid foundation system.
**Specifications:**
- Slab thickness: 5"-6"
- Post-tension tendons per design
- Thickened edges: 18"-24" deep
- Specialized reinforcement layout
**Advantages:**
- Superior crack resistance
- Handles expansive soils
- Spans weaker areas
- Longer clear spans
**Best For:**
- Ontario's expansive soil areas
- Larger open floor plans
- High-performance requirements
**Cost:** $16-$25 per square foot
Waffle/Ribbed Slab **Stiffened Foundation System**
Grid of thickened ribs creates stiff foundation without deep excavation.
**Specifications:**
- Surface slab: 4"
- Ribs: 8"-12" wide x 12"-24" deep
- Grid spacing: 4'-6' typical
- Void forms between ribs
**Advantages:**
- Handles soil movement
- Economical stiffening
- Reduced excavation
- Good in expansive soils
**Best For:**
- Moderate to severe expansive soils
- Cost-effective alternative to PT
- Sites with variable conditions
**Cost:** $12-$18 per square foot
Ontario Soil Considerations for Slab Foundations
Soil Types in Ontario
**Alluvial Soils:**
- Common in valley areas
- Generally good bearing
- May contain variable layers
- Watch for groundwater
**Expansive Clays:**
- Present in many Ontario areas
- Require enhanced foundation design
- Post-tensioned or stiffened slabs recommended
- Moisture management critical
**Fill Soils:**
- Common in developed areas
- Require proper certification
- May settle over time
- Engineering verification needed
Geotechnical Requirements
Most Ontario slab projects require:
- Soils investigation report
- Bearing capacity determination
- Expansion potential testing
- Subgrade preparation specifications
Slab Foundation Engineering Process
Phase 1: Site Analysis
**Information Gathering:**
- Review geotechnical report
- Understand soil bearing capacity
- Evaluate expansion potential
- Check groundwater conditions
**Building Analysis:**
- Calculate structural loads
- Identify load-bearing walls
- Review architectural plans
- Determine slab requirements
Phase 2: Foundation Design
**Structural Calculations:**
- Load analysis
- Footing sizing
- Slab thickness determination
- Reinforcement design
- Seismic compliance
**Design Decisions:**
- Foundation type selection
- Edge beam configuration
- Interior footing layout
- Reinforcement specification
Phase 3: Construction Documents
**Foundation Plan:**
- Dimensioned layout
- Footing locations and sizes
- Slab thickness zones
- Reinforcement schedule
**Structural Details:**
- Edge beam sections
- Interior footing details
- Slab-to-wall connections
- Reinforcement placement
**Specifications:**
- Concrete requirements
- Subgrade preparation
- Vapor barrier installation
- Curing requirements
Phase 4: Construction Support
**Pre-Construction:**
- Contractor coordination
- RFI responses
- Subgrade approval
**During Construction:**
- Inspection coordination
- Problem resolution
- Plan clarifications
Slab Foundation Costs in Ontario
Construction Costs
| Slab Type | Cost per SF | 2,000 SF Home | |-----------|-------------|---------------| | Monolithic | $8-$12 | $16,000-$24,000 | | Stem Wall | $14-$20 | $28,000-$40,000 | | Post-Tensioned | $16-$25 | $32,000-$50,000 | | Waffle Slab | $12-$18 | $24,000-$36,000 |
Engineering Costs
| Service | Cost Range | |---------|------------| | Foundation Design Only | $2,000-$4,000 | | Complete Structural Package | $5,000-$9,000 | | Post-Tension Design | $3,500-$6,000 | | Construction Observation | $150-$250/hour |
Slab Foundation Construction in Ontario
Site Preparation
**Clearing and Grading:**
- Remove vegetation and debris
- Grade to design elevation
- Achieve proper drainage slope
**Subgrade Preparation:**
- Scarify existing soil
- Moisture condition to optimum
- Compact to 90%+ density
- Proof roll to verify
**Base Course (if required):**
- Clean gravel or crusite
- 4"-6" thickness typical
- Compacted thoroughly
- Level surface
Forming and Reinforcement
**Edge Forms:**
- Straight and level
- Properly braced
- Height per plans
- Clean and oiled
**Reinforcement:**
- Per engineering plans
- Proper spacing and cover
- Supported on chairs
- Tied securely
**Embedded Items:**
- Anchor bolts at specified locations
- Sleeves for utilities
- Hold-downs per plans
- Proper positioning
Concrete Placement
**Ready-Mix Requirements:**
- Specified strength (typically 2,500-3,500 PSI)
- Proper slump (4"-6" typical)
- Temperature limits
- Delivery timing
**Placement:**
- Continuous pour preferred
- Proper consolidation
- Bull float finish
- Control joint cutting
**Curing:**
- Begin immediately after finishing
- Moist cure or curing compound
- Minimum 7 days
- Protect from extreme conditions
Ontario Building Requirements
Permits Required
- Building permit for all foundations
- Grading permit if significant earthwork
- Engineering plans required
Plan Check Process
- Submit complete plans
- 2-4 week review typical
- Address corrections
- Obtain approval
Required Inspections
- Footing excavation
- Reinforcement placement
- Pre-pour (forms and embeds)
- Anchor bolt/hold-down
- Final foundation
**City of Ontario Building Department:** 303 East B Street Ontario, CA 91764 (909) 395-2408
Common Slab Foundation Problems in Ontario
Cracking
- Shrinkage (normal)
- Settlement (soil movement)
- Structural (overload)
**Prevention:**
- Proper mix design
- Adequate reinforcement
- Control joints
- Proper curing
Settlement
- Poor soil preparation
- Expansive soil movement
- Fill consolidation
**Prevention:**
- Proper subgrade preparation
- Appropriate foundation type
- Drainage management
Moisture Issues
- Missing vapor barrier
- Improper drainage
- Rising groundwater
**Prevention:**
- Quality vapor barrier installation
- Proper site grading
- Perimeter drainage
Our Ontario Service Area
AAA Engineering Design serves Ontario and the Inland Empire:
**Primary Service Area:**
- Ontario - All neighborhoods
- Rancho Cucamonga (5 miles north)
- Fontana (8 miles east)
- Upland (8 miles north)
- Chino (10 miles south)
**Office Location:** Stanton, CA (Central Orange County) **Travel:** On-site consultations throughout San Bernardino County
Why Choose AAA Engineering Design
**Slab Expertise:** Extensive experience designing slab foundations for Inland Empire conditions.
**Local Knowledge:** Familiar with Ontario soil conditions and building requirements.
**Complete Service:** From initial design through construction support.
**Code Compliance:** All designs meet California Building Code requirements.
**Responsive:** Quick turnaround on plans and plan check responses.
Frequently Asked Questions
**How thick should my slab be?** Standard residential slabs are 4" minimum, but 5"-6" is recommended for better performance. High-traffic or heavy-load areas may require thicker slabs.
**Do I need post-tensioned slab in Ontario?** It depends on soil conditions. Many Ontario properties benefit from post-tensioning, but it's not always required. Geotechnical recommendations guide this decision.
**How long before I can build on the slab?** Concrete reaches adequate strength for construction in 7 days, but full cure takes 28 days. Follow your engineer's and contractor's guidance.
**Can cracks in new slabs be normal?** Small shrinkage cracks are normal and typically not structural concerns. Large cracks or patterns of cracking warrant evaluation.
Start Your Ontario Slab Foundation Project
Quality slab foundation engineering ensures your building starts on solid ground. Contact AAA Engineering Design for professional foundation design.
**Get Your Free Consultation:**
- **Phone:** (949) 981-4448
- **Email:** info@aaaengineeringdesign.com
- **Service Area:** Ontario, San Bernardino County, and all of Southern California
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