Underpinning means adding support under an existing foundation so it rests on stronger or deeper soil. It is the fix for settlement that will not stop on its own. Chula Vista Structural installs underpinning for homes across the city. Pier type, depth, and spacing should come from an engineered design, so we coordinate with licensed engineers as needed on every underpinning job where the City or site conditions call for one.
When underpinning is the right answer
Underpinning is a big step, and it is not always needed. It usually makes sense when:
- Part of the house has settled and floor readings show it is still going down
- The soil near the surface is weak fill, soft alluvium, or clay that cannot be controlled with moisture alone
- A soils engineer has found that firmer soil lies deeper
- A footing near a slope needs to reach past the slope’s weaker soil
- A remodel or addition will add weight the old footing cannot carry
It usually is not the first step when the problem is mostly water. If downspouts, grading, or a leak are driving movement, fixing those may be enough. We will say so. See foundation drainage.
Why pier choice is tricky on Chula Vista clay
Expansive clay pushes up as well as down. The Otay Formation in eastern Chula Vista contains bentonite that swells when wet (California Geological Survey), and geotechnical reports for the area describe those layers as weak when wet. A pier going through that clay can get gripped and lifted when the clay swells, or lose support near the top when it shrinks.
Engineers handle this in the design: how deep the pier goes below the active clay zone, what it is made of, and how it connects to the house. That is why we do not sell a single pier product for every home. The soil at your lot decides.
On canyon-edge lots, the question is different. There, a pier may need to reach below fill or past a zone that could creep downhill. The City’s hazard plan points to canyon slopes in older developed areas as the main landslide concern. A soils engineer’s input matters even more here. See canyon-edge and slope foundations.
Types of underpinning
Push piers (resistance piers). Steel pipe sections pushed into the ground using the weight of the house, until they hit firm soil. Common for settled footings.
Helical piers. Steel shafts with screw-like plates, turned into the ground. Useful where the house is light or where installation needs to be precise.
Drilled concrete piers. Holes drilled and filled with reinforced concrete. Often chosen for clay because they can be designed to reach below the zone that swells.
Mass concrete underpinning. Digging under the footing in sections and filling with concrete to make it deeper. Older method, still useful in some spots.
Grade beams. Concrete beams that span between piers and carry the wall above.
The engineer picks from these based on soil data, loads, access, and the goal. We build what the design calls for.
What the work looks like
- Evaluation and soils data. Floor levels, crack mapping, and usually a soils report.
- Design. The engineer specifies pier type, depth, spacing, and connection details.
- Permit. Underpinning is structural work and generally needs a City of Chula Vista building permit. Bonita and Sunnyside go through the County.
- Excavation. We dig at planned spots along the foundation. Inside work, if needed, means cutting through floors.
- Installation. Piers go in, brackets connect them to the footing, and the house is supported. If the design allows, the house may be raised partway back.
- Inspection and backfill. City inspections at the required stages, then we backfill and clean up.
- Drainage fixes. So water does not undermine the new work.
What underpinning will not do
It will not stop clay from moving under the middle of a slab if only the edges are pinned. It will not fix a slope that is moving as a whole. And it will not make a house perfectly level if it has been out of level for decades. Honest expectations matter here.
Underpinning questions
How many piers does a house need?
That comes from the engineer’s design, based on the length of foundation that needs support and the loads on it. It varies a lot from house to house.
Can underpinning be done on a post-tension slab?
Sometimes, with an engineer’s design that accounts for the tendons. See post-tension slab problems.
Do I have to move out?
Usually not for exterior pier work. Interior work can be more disruptive. We explain before you commit.
What drives the cost?
Pier count, depth, soil, access, engineering, and permits. Our cost factors page explains each one without made-up price lists.
Talk to us about underpinning
Tell us what is settling and whether you already have a soils or engineering report. We will review it and visit.
Sources for local facts
- California Geological Survey, San Diego 30’×60’ Quadrangle pamphlet (Otay Formation)
- Ninyo & Moore geotechnical report, City of Chula Vista Clerk records (2019)
- County of San Diego 2023 Hazard Mitigation Plan, City of Chula Vista Annex
- City of Chula Vista Development Services permits page