Why Footing Strength Matters for Two-Story ADUs
When you’re building a two-story accessory dwelling unit (ADU), the integrity of your structure starts from the ground up. Specifically, it starts with your footings and the concrete PSI rating specified in your structural plans. These two elements determine the load-bearing capacity and long-term durability of the foundation.
Understanding Concrete PSI in Structural Plans
Your approved plan set will always specify the required concrete PSI. For larger or multi-story buildings, this will typically range between 3,000 and 4,000 PSI. Using the wrong PSI concrete mix can compromise structural integrity and lead to costly rework or failed inspections.
- 3,000 PSI: Often used for standard residential slabs or light-duty footings
- 3,500 PSI: Ideal for most ADUs, especially single-story structures
- 4,000 PSI: Required in many two-story applications or where extra load capacity is necessary
Always confirm the spec with your engineer or general contractor before the pour. Ordering the wrong mix can delay your timeline and increase costs.
Set Your Rebar Before Pouring
Concrete strength is only one part of the equation. Properly placed and tied rebar ensures that the concrete resists tension and prevents cracking or failure over time. For two-story ADUs, rebar layout must be precise, aligned to plan, and checked before any concrete is poured.
Typical checks before pouring:
- Rebar is properly spaced and tied
- Rebar sits on appropriate chairs or dobies (not touching soil)
- All corners have hooks or bends per structural spec
- Anchor bolts are set at correct spacing and elevation
Common Mistakes to Avoid
- Pouring with the wrong PSI concrete for a two-story load
- Missing or loose rebar ties that shift during pour
- Improper clearance from the edge of footing or from soil contact
- Failing to inspect formwork for bowing or misalignment
Final Tip
Strong ADU foundations start with precision. Use the right PSI mix, inspect rebar before your pour, and never assume your foundation crew has everything right without a double-check. These small steps make a major difference in the longevity and safety of your two-story ADU.
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Watch the video above to see how we handle concrete prep and PSI validation on real Orange County projects.
