You keep seeing the same words: underpinning, piers, helical, eh . . . bell-bottom what now? Nobody handed you a dictionary for this stuff. You’re tired of nodding along in conversations you don’t fully follow.
At Anchor Foundation Repair, we’ve spent decades explaining these terms to Brazos Valley homeowners. You just want a straight answer. Our Texas clay soil makes this stuff extra confusing, so we built our whole approach around plain-English explanations.
Consider this your quick-reference glossary. Search for the term you’re stuck on, get a plain answer, and move on with your day.
What Does “Underpinning” Mean in Foundation Repair?
Underpinning means adding new support under an existing home’s foundation. The goal is to stop it from sinking or shifting further. It’s not one method. It’s the whole category of methods.
Think of it as an upgrade added after the fact. Your home didn’t have this support when it was built. Now that the foundation has moved, underpinning adds deeper support. Those supports reach past unstable, shrink-swell clay into ground that stays firm all year.
If a contractor says your home needs underpinning, that means it needs some form of foundation repair. It doesn’t say which method. Ask a follow-up question.
What Are “Piers” and How Are They Different From Underpinning?
Piers are the physical supports used in underpinning. Underpinning is the process. Piers are one of the tools that can make it happen.
Every pier is a type of underpinning. But not every underpinning method uses piers. Slab jacking, for example, doesn’t. You might also hear the word “pilings.” People often use it to mean the same thing as piers, though pilings usually point to one specific method.
Bottom line: underpinning is the umbrella term. Piers are one type of support used underneath it.
What’s the Difference Between Drilled Piers, Helical Piers, and Pressed Pilings?
These three terms are easy to get mixed up, especially when you don’t understand how they’re even different – but each type of support is truly a different concept. Here’s what separates them:
- Drilled piers: A cylindrical shaft drilled down to more stable soil. Crews fill it with steel-reinforced concrete. It most often has a flared “bell” base at the bottom for extra hold and those are called bell-bottom piers. On occasion, some piers are not belled.
- Helical piers: A steel shaft with screw-like plates. Machines twist it into the soil. It works well where drilling isn’t practical, though it’s less common in areas with heavy clay.
- Pressed pilings: Concrete or steel sections pressed into the ground one by one, commonly about 6 inches wide and 12 inches long. Machines push them into the ground until they encounter a certain amount of resistance they call “point of refusal”.
Depth and material matter here. Drilled piers rely on reaching stable soil for their hold, while the bell-shape at the bottom locks things in place. Pressed pilings rely more on friction, and friction can hold up differently over time in expansive clay when moisture levels change.
What Is a “Bell-Bottom” Pier?
A bell-bottom pier is a drilled pier with a flared base shaped like a bell. That shape isn’t decorative. It’s built to resist uplift. Uplift happens when wet clay soil swells and pushes against the pier.
The wider base also spreads your home’s weight over more surface area. That helps with long-term stability. This design is common in Texas because it’s built to handle our shrink-swell soil cycles.
If you’re comparing quotes and one contractor mentions “bell-bottom” and another doesn’t, ask what shape their pier base uses. It’s a real engineering difference, not a marketing term.
What Do “Slab Jacking” and “Polyjacking” Mean?
Both terms describe lifting a sunken slab. Workers inject material underneath it, usually expanding foam or a cement-based slurry. Polyjacking is the name for the foam version.
This method lifts the slab, but it doesn’t add deep support the way piers do. It’s a good fit for minor settling on the interior of a home or exterior flatwork like sidewalks and driveways. It’s not a substitute for deep underpinning when a foundation has real structural movement.
If a contractor recommends slab jacking for serious settlement, ask why. It’s the right tool for the right situation, and the wrong tool for the wrong one.
Foundation Repair Terms at a Glance
Bookmark this for your next contractor conversation:
- Underpinning: The general process of adding support beneath a foundation
- Pier: Any deep support structure used in underpinning
- Drilled pier: A concrete shaft drilled 10 to 12 feet into stable soil
- Bell-bottom pier: A drilled pier with a flared base that resists uplift
- Helical pier: A steel shaft with screw-like plates twisted into the ground
- Pressed piling: Concrete or steel sections pushed into the ground with hydraulic force
- Slab jacking / polyjacking: Lifting a slab by injecting foam or slurry underneath it
Knowing these terms helps you spot misleading claims and compare contractor proposals on facts, not confidence.
Curious what’s actually under your house? The USDA’s Web Soil Survey tool lets you look up your local soil type by address, free of charge.
Bring These Foundation RepairTerms Into Your Next Convo
Now you’ve got a working vocabulary. Underpinning is the umbrella process. Piers are the physical supports. Drilled, helical, bell-bottom, and pressed pilings are the specific methods contractors use to get the job done.
You’ll walk into your next estimate knowing what to ask and why the answer matters. That’s the difference between nodding along and actually deciding what’s right for your home.
We’ve built Anchor’s reputation on plain language, not industry code, since 1985. If you’re ready to see how these terms apply to your own home, get a straightforward assessment from our team.