In Silicon Valley and the greater Bay Area, every home has a story and that story starts with its foundation.
As an architect-turned realtor, I often meet homeowners who panic when they see cracks or uneven floors. But not every crack means danger, and not every tilt means failure.
Let’s break down the different types of foundations, what those cracks really mean, and how to tell if your home is stable or still moving.
The Three Main Types of Foundations
1. Slab-on-Grade
A Slab-on-Grade foundation is a solid concrete slab poured directly on the ground. It’s common in newer homes: strong, termite-resistant, and low-maintenance. But because the concrete sits directly on soil, if the ground shifts, it can crack and is difficult to repair from underneath.
2. Crawl Space Foundation
This design elevates the home slightly, leaving a ventilated space underneath for plumbing, electrical, and HVAC systems. It’s easier to maintain and adjust, but moisture control is key especially in coastal Bay Area climates.
3. Post-and-Pier Foundation
Common in hillside and older Bay Area homes, this system rests on a grid of concrete or wooden piers. It’s flexible and accessible, ideal for uneven terrain. However, over decades, piers can shift slightly, resulting in mild sloping that’s normal and repairable.
Foundation Cracks: When to Worry and When to Relax
Cracks are one of the most misunderstood parts of a foundation inspection.
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Hairline cracks (<¼ inch): Usually harmless. They occur as concrete cures and dries.
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Wider cracks (>¼ inch): Worth inspecting. If you can insert a pencil tip or if it’s expanding, it might signal movement.
Vertical cracks usually come from natural settlement and are often non-structural.
Horizontal cracks, however, can indicate lateral soil pressure or rebar corrosion.
These may require cleaning out rusted steel and filling with epoxy or concrete repair material.
💡 Pro Tip: Don’t just ask “Is there a crack?”, ask “Is it still moving?”
Uneven Floors: How Much Is Too Much?
If you drop a marble on your floor and it rolls, don’t panic. A little slope is very common, especially in older Bay Area homes.
✅ Acceptable range: about 1 inch over 20 feet
🏗️ New construction standard: roughly 1/8 inch per 10 feet (much stricter)
Unless the slope is getting worse or causing functional issues (like doors sticking or walls cracking), it’s not considered a foundation failure.
Historical Settlement: Stability Over Time
One of the most reassuring signs of a healthy home is no change over time.
I once reviewed a property where the inspector compared a new report with one from ten years ago. Same slope, same cracks, no movement. That’s what engineers call historical settlement, normal settling that happened years ago and is now stable.
This is especially common in Foster City, a community built on man-made fill. Mild tilting is widespread there, but as long as it hasn’t changed for years, the structure is stable and safe.
🏠 Key takeaway: In Foster City, it’s not unusual for one out of every two homes to show some settlement. It’s part of the local soil condition, not necessarily a defect.
Repair Options for a Tilted but Stable Home
If your house has tilted slightly but is no longer shifting, there are several ways to level it depending on its structure:
✅ Self-Leveling Compound
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For concrete slab foundations, this liquid cement smooths uneven floors (up to about 1 inch difference).
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Fast, affordable, and great for surface corrections.
✅ Shimming or Adding Sleepers
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Used in crawl space or post-and-pier homes, wood shims or beams are added beneath floor joists to even out the surface.
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A practical and common method in older houses.
✅ Hydraulic Jacking (Foundation Lifting)
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For more significant correction, professionals can lift the structure using hydraulic jacks, then reinforce the supports below.
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This method, known as house jacking or foundation leveling, works well for major remodels but may cause minor wall or door cracks as the house readjusts.
The Bottom Line
When it comes to foundations, the goal isn’t perfection, it’s stability.
So before jumping to conclusions, ask yourself three key questions:
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Is the issue getting worse?
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Has it been stable for years?
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Is the soil underneath still moving?
If the answer is yes, it’s stable, then even a slightly tilted home can remain safe, functional, and valuable for decades.
Final Thought
A foundation isn’t just concrete and rebar. It’s the beginning of a home’s story. Understanding it helps you make smarter decisions, whether you’re buying, selling, or maintaining a property.
And that’s where an architect’s eye in real estate makes all the difference. Seeing not just what’s visible, but what’s possible.