What Causes an Uneven Foundation?
Foundations become unlevel when the soil beneath them moves unevenly. Common causes:
Differential soil settlement - clay soil shrinks more in a dry area (beneath a drought-stressed tree, under a downspout that dumps water to one side) than in adjacent areas. The differential creates tilt.
Localized void formation - erosion from a plumbing leak or drainage problem creates a void beneath the slab. When the concrete spans that void, it eventually cracks and drops.
Expansive soil heaving - moisture reaching one area but not another causes differential clay expansion. The wet area heaves while the dry area stays put.
Original construction deficiencies - fill soil placed inadequately compacted beneath a slab consolidates over time under the structure’s load.
Leveling Methods
Pier-Based Lifting
For foundations with significant settlement (more than 1 inch differential, or settlement caused by underlying soil instability), piers are installed and used as jacking points to lift the low areas.
When appropriate: Ongoing soil movement; significant structural settlement; foundation that needs stabilization, not just a one-time lift.
Process: Piers are installed to stable bearing depth. Hydraulic jacks at each pier simultaneously lift the structure. Grade is monitored with a laser level.
Cost: $8,000-$25,000 for most residential leveling projects using piers.
Mudjacking (Slab Jacking)
Mudjacking pumps a cement-soil slurry through small holes drilled in the slab to fill voids and lift sunken sections. The slurry cures into a relatively stable material.
When appropriate: Minor settling (under 2 inches); stable soil that has simply lost contact with the slab due to void formation; garage slabs, walkways, pool decks.
Limitations: The slurry adds weight to already-soft soil; not effective for ongoing settlement caused by unstable soil; results may not be permanent in expansive clay regions.
Cost: $500-$3,000 for residential applications.
Polyurethane Foam Injection
Foam injection is a modern mudjacking alternative - expanding polyurethane foam is injected through small holes and expands to fill voids and lift the slab. Lighter than slurry, faster to cure (often usable within 15 minutes), and more precisely controllable.
When appropriate: Smaller areas; garage floors; basement floor sections; where adding weight to the subgrade is a concern.
Cost: $500-$2,500 for residential applications.
Crawlspace Shimming and Pier Adjustment
For pier and beam foundations, leveling is achieved by shimming settled piers back to level, replacing failed piers, or adjusting adjustable steel column jacks. This is the standard approach for any pier and beam home with uneven floors.
Cost: $150-$600 per pier adjusted or replaced; $1,500-$8,000 for a comprehensive crawlspace leveling project.
How Much Can a Foundation Be Lifted?
This is the most common question contractors face - and the honest answer is: it depends.
Practical constraints on lifting include:
- Plumbing connections - aggressive lifting can shear or crack slab-embedded plumbing lines. Most contractors limit lift attempts near plumbing areas.
- How long it’s been settled - a foundation that settled 10 years ago has had finishes, plumbing, and framing adapt to the new position. Lifting back aggressively can create new damage.
- Structural connections - wood framing connected to a slab or footing can be cracked if the lift is too abrupt.
Most experienced contractors target reduction of differential - narrowing the gap between the high and low points - rather than complete restoration to original grade. A result within 1/2” of level is generally considered a successful leveling outcome.
After Leveling: Cosmetic Repairs
Foundation leveling does not close interior drywall cracks, re-align doors and windows, or fix damaged tile. After the foundation is leveled and stable, cosmetic repairs can be made with confidence they will hold. Budget separately for interior cosmetic repair.