A sagging floor rarely drops overnight. It sinks a fraction of an inch at a time as a girder deflects, a post settles, or a crawl space pier rots, and by the time a marble rolls across the kitchen the problem is years old. House leveling jacks are the tools contractors use to lift that framing back toward level and hold it there permanently. Used correctly, they can fix a bouncy floor for a few hundred dollars. Used carelessly, they crack drywall, pop tile, and can drop a house on the person underneath. This guide explains the types, ratings, costs, and safe methods so you know what the job involves before you pick up a wrench.
- What House Leveling Jacks Actually Do
- Types of Leveling Jacks and Posts
- The Footing Is More Important Than the Jack
- How Fast Can You Lift a Floor?
- Step-by-Step: Installing a Screw Jack Under a Sagging Beam
- When to Call a Licensed Professional
- How Leveling Affects Your Floors
- Cost Summary
- Frequently Asked Questions
- The Bottom Line
What House Leveling Jacks Actually Do
House leveling jacks transfer load from the floor framing down to a footing, and they let you adjust height in small increments. They are used under a main beam (girder), under individual joists that have sagged between supports, or beneath a floor where an original post has rotted or been removed. Some are temporary lifting tools; others are designed to stay in place for decades.
The distinction matters. A hydraulic bottle jack is great for lifting but is never a permanent support, because seals can bleed down over time. A threaded steel screw jack or adjustable steel column is built to carry load indefinitely once it is set. Most professional jobs use both: a bottle jack does the lifting, and a screw jack or post takes over the load.
Types of Leveling Jacks and Posts
Adjustable Steel Screw Jacks
Crawl space screw jacks, sometimes called floor jacks or jack posts, are the most common permanent fix. They have a heavy steel base plate, a tube, and a 1-1/4 to 1-1/2 inch threaded rod with a top plate. Typical adjustment ranges run from about 12 to 24 inches for short crawl-space models and up to 8 feet for basement columns. Load ratings of 25,000 to 50,000 lb at short heights are common, although capacity drops as height increases. Expect to pay $40 to $120 per jack for short units.
Telescoping Jack Posts
These are the familiar gray steel columns with a pin-and-hole coarse adjustment and a threaded top for fine adjustment. They sell for $40 to $90 at home centers. Many are labeled for temporary use only; check the stamp. For permanent basement support, local codes usually want a listed, permanently rated column, often filled with concrete or locked with a set pin so it cannot be adjusted afterward.
Hydraulic Bottle Jacks
Bottle jacks of 12 to 20 tons ($40 to $150) provide the actual lifting force. You place one on a solid pad beside the screw jack, lift a small amount, then snug the screw jack under the load. Never leave a bottle jack holding a house overnight.
Engineered Pier Systems
Foundation repair companies use proprietary adjustable steel piers set on engineered footings or helical piles. These solve settlement from soil movement, not just sagging framing, and they come with warranties. Pricing typically lands between $1,000 and $3,000 per pier installed.
The Footing Is More Important Than the Jack
A 50,000 lb jack sitting on a 4-inch slab or a paver in loose dirt will simply punch downward. The load has to spread over enough soil to support it. A common crawl-space approach is a poured concrete pad of about 24 x 24 x 12 inches, though your local code and soil conditions set the real requirement. Precast 16 x 16 inch footing blocks ($8 to $15) can work for lighter loads on firm soil.
In a basement, a typical 3-1/2 or 4 inch floor slab is not designed as a footing. Cut out a section and pour a proper footing under any new permanent post. If you skip this, you may see the slab crack and the post sink within a year, putting you right back where you started.
How Fast Can You Lift a Floor?
Slow is the rule. Framing, drywall, plaster, and tile have taken a set over years, and they need time to follow the lift. Many contractors limit lifts to about 1/8 inch per week, some go as far as 1/4 inch per week on unfinished areas, and a quarter turn on a screw jack every few days is a common schedule. Watch for these warning signs and stop if you see them:
- New cracks forming at door corners or along drywall seams
- Doors that suddenly bind in their frames
- Popping or cracking sounds from the framing
- Tile grout cracking on the floor above
- The jack base sinking or tilting
Some sag should not be fully removed. A beam that has deflected 1-1/2 inches over 40 years may be damaged or undersized. Pushing it to dead level can split it. Often the smart goal is to lift just enough to remove the bounce and the visible dip, then add support so it cannot sag again.
Step-by-Step: Installing a Screw Jack Under a Sagging Beam
- Find the low spot. Stretch a string line or use a 6-foot level and a laser along the underside of the beam to identify how much and where it sags.
- Prepare the footing. Dig and pour a concrete pad, or confirm an existing footing is sound. Let new concrete cure at least 7 days, ideally longer.
- Set the jack. Place the base plate on the pad, plumb the post in two directions, and run the screw up until it is snug against the beam. Add a steel or hardwood plate on top to spread the load.
- Lift gradually. Use a bottle jack beside the screw jack for the heavy lifting if needed, then snug the screw jack. Turn no more than the planned increment.
- Monitor and repeat. Mark the date and height on the post with a paint pen. Recheck the house for cracks before each adjustment.
- Lock it in. Once the floor is where you want it, secure the top plate to the beam with lag screws and the base to the footing so it cannot kick out.
When to Call a Licensed Professional
Lifting a house is structural work. Call a licensed structural engineer or a licensed foundation repair contractor before you jack anything if you see any of the following: stair-step cracks in block walls, horizontal cracks in a basement wall, a gap between the sill plate and foundation, sloping of more than about 1 inch over 20 feet, or sagging near a bearing wall that carries the second floor or roof. An engineer’s site visit usually costs $300 to $800 and tells you whether you have a framing problem or a soil and foundation problem.
That distinction decides the fix. Jacks correct sagging framing. They do not stop a foundation that is still moving. Most jurisdictions also require a permit for adding or replacing structural posts, and an inspector will want to see the footing before it is covered. Never work under a raised load that is supported only by a hydraulic jack, and use cribbing (stacked 6×6 timbers) as a safety backup under anything you have lifted.
How Leveling Affects Your Floors
Flooring is often what alerts homeowners to structural sag. Hardwood gaps open over a low beam, laminate click joints separate, and tile cracks along a line directly above a girder. Correct the structure before replacing flooring; a new floor laid over a sagging frame will fail the same way. Most manufacturers require subfloor flatness within 3/16 inch in 10 feet for plank floors and 1/8 inch in 10 feet for large-format tile.
After the framing is stable, you can address minor remaining dips with self-leveling underlayment ($30 to $45 per 50 lb bag) or by sanding high spots in the subfloor. Wait several weeks after the last jack adjustment so the house settles into its new position before you install finish flooring.
Cost Summary
| Item | DIY cost | Professional cost |
|---|---|---|
| Screw jack (each) | $40 to $120 | $300 to $800 installed |
| Concrete footing pad | $30 to $80 | $200 to $600 |
| Sistered joist | $50 to $150 | $300 to $700 |
| Engineered pier | Not DIY | $1,000 to $3,000 |
A typical crawl-space sag repair with three to six jacks on new footings runs $1,500 to $5,000 from a contractor. Full foundation stabilization with piers can reach $10,000 to $25,000 or more.
Frequently Asked Questions
Are house leveling jacks a permanent fix?
Steel screw jacks and permanently rated columns on proper footings can be permanent. Hydraulic bottle jacks and posts labeled for temporary use are not. Always check the manufacturer’s label and your local code.
How many jacks do I need under a sagging floor?
It depends on the beam size and span, but posts are commonly spaced every 6 to 8 feet under a girder. An engineer can specify spacing based on the actual loads.
Can I use house leveling jacks without a permit?
Many jurisdictions require a permit for new structural posts or footings. Call your local building department before you start; the fee is small compared with the cost of redoing failed work.
How long does it take to level a house with jacks?
Because lifts should be gradual, leveling a noticeable sag often takes several weeks to a few months of small adjustments rather than a single afternoon.
The Bottom Line
House leveling jacks are simple tools that solve a common problem, but the jack is only one part of the system. A solid footing, a slow lift, and an honest diagnosis of why the floor sagged in the first place determine whether the repair lasts. Get an engineer’s opinion when the cause is unclear, and fix the structure before you invest in new flooring above it.
