Bowed basement walls make it difficult to finish a basement or add living space. More importantly, bowed basement walls are a structural hazard. In most cases, professionals should take care of the issue and perform any repairs on bowing basement walls. As a do-it-yourselfer, you'll want to know the specifics of how professionals will fix the problem, plus find out ways to prevent further bowing.
What Bowed Basement Walls Are
Bowed basement walls are masonry walls that bow or curve from the outside to the inside. If standing inside the basement and looking at the bowed wall, you should see a convex or bulging wall. This problem is sometimes called inward deflection.
Bowed basement walls often are cracked, too. Either vertical or horizontal cracks may be present, but mostly they are horizontal due to the direction of the bend in the walls. These cracks may expand in the rainy season and close up in the dry season.
How to Assess Bowed Basement Walls
Before speaking to a foundation repair company or just to get an idea of the cost of repairing the bowed basement walls, it helps to measure the degree of deflection. All you need is a ruler and a weighted string.
- Hold a string weighted with a heavy bolt at the bottom against the basement ceiling.
- Move the string toward the wall until it touches the most inwardly bowed section of the wall.
- Have an assistant use a ruler to measure the distance from the string to the most outward section of the wall. The resulting figure is the deflection distance.
Two inches is considered minor deflection. From 2 to 4 inches is moderate deflection; this can be corrected with tie-backs, wall anchors, or steel beams. Walls that deflect 6 inches or more are severely bowed and often must be replaced.
What Causes Bowed Basement Walls
Bowed basement walls are caused by pressure from the exterior pushing the walls inward. The most common cause of pressure on basement walls is water.
Exterior soil adjacent to the side of the basement wall becomes saturated with water during rainy times. This waterlogged soil becomes heavy and expands. This expansion pushes against the basement wall from the outside.
This problem of hydrostatic pressure is more pronounced with expansive soils—those that are rich in clays. The U.S. Midwest, South, and California’s Central Valley are heavy in clay soils. Sandy soil drains well and is not expansive.
Frozen soil expands, as well. When a large section of soil next to a basement wall freezes, it may push against the upper section of the basement wall.
Extremely heavy items placed on top of the soil adjacent to the basement wall can push down on the soil, which also has the effect of pushing the soil outward. Ordinary exterior items such as decks will not cause this, but heavy machinery or vehicles parked long-term may cause this.
When to Repair Bowed Basement Walls
Because bowed basement walls are mostly caused by waterlogged or frozen soil, it is best to wait until the driest and warmest possible months in your area. In most regions, this period ranges from June to September. But if the problem is severe and water is finding its way into your basement, hire a professional to repair the bowed walls immediately.
Cost of Repairing Bowed Basement Walls
The cost of repairing both basement walls depends on the severity of the bowing and the area where you live.
Walls that bow farther inward require different, more expensive repair methods, which may include extensive outside digging. If you live in an area where many basements experience bowing, there is a more active market for this type of work—so, more choices for you and the potential of receiving competitive bids.
- Low: For basement walls that bow only slightly, the cost of repairs may run between $4,000 and $8,000.
- Mid: For mid-range wall bows from 3 to 4 inches, the cost could run between $8,000 and $15,000. If helical tie-backs are required, each tie-back can cost as low as a couple hundred dollars to $1,000, with total project averages running around $18,000 to $20,000.
- High: Severely bowed basement walls with 6 inches or more of deflection likely will cost $25,000 or more to fix, as the entire basement wall would need to be replaced.
Codes and Permits
Most communities require building permits for work involving basement walls since basement walls are foundational structures.
Large-scale water mitigation measures outside the house, such as adding storm catchments or building French drains, may or may not be permitted work in your area.
Smaller scale water mitigation fixes such as repairing gutters or regrading the ground are usually not permitted activities.
All methods of repairing or replacing bowing basement walls are inherently dangerous because the structural stability of the house depends on the work. The best way to stay safe is to have all work done by professionals in conformance with local codes, and for that work to be permitted, inspected, and approved by municipal inspectors.
How to Fix or Stabilize Bowing Basement Walls
After you assess the severity of the bowing, there are three main ways a professional will fix or mitigate the problem: basement wall braces (which push or hold the wall from the inside); anchor systems (which pull on the wall from the outside, correcting it); and basement wall replacement.
Basement Wall Braces
Carbon fiber straps run vertically from the top of the basement wall to the bottom, at about every 4 feet along the wall. Straps are placed on the inside of the basement walls only; no digging is required. Adhered to the basement wall with epoxy, the straps can be covered or painted.
Carbon fiber straps help stabilize the wall when working in conjunction with water mitigation measures. Straps alone do not correct the basement wall bowing.
Straightening and Strapping
Carbon fiber strap stabilizers are sometimes installed after the basement wall bowing has been corrected.
From the outside, soil is excavated to provide working access. Then, on the inside of the basement, hydraulic jacks push the basement walls outward to correct them. Once corrected, the walls are strapped.
Steel I-beams are run vertically along the basement wall, spaced at about every 4 feet. At the bottom, the beams are bolted into the floor. At the top, the beams are bolted to the house’s joists or beams.
Steel beams are attached in conjunction with excavating soil alongside the wall exterior. This is necessary so that the wall can be pushed back to vertical and corrected. Since the beams remain in place, this is best for unfinished basements.
Basement Wall Anchor Systems
Wall Plate Anchors
For basement wall bows that deflect up to 2 inches, wall plate anchors are a good option. Large metal plates are fastened about every 5 feet along the basement wall. Steel rods extend horizontal and level at least 10 feet outward from the basement and are secured in the ground.
Wall plate anchors require substantial exterior digging. If you have any obstructions in the 10-foot wide border around the house, such as easements or sewer lines, you cannot install wall anchors.
Otherwise, wall anchors are an effective, permanent solution to bowed basement walls. Plus, they allow stud wall systems to be built on the inner basement walls—important if you want to finish the basement.
Best for badly deflected basement walls, helical tie-backs are similar to wall anchors. Both have metal plates on the inside of the basement walls and rods that extend into the ground outside.
But helical tie-backs differ in that they are installed entirely from inside the basement. Holes are drilled at an angle downward. Rods up to 21 feet long are inserted, with the ends attached to the wall plates.
Helical tie-backs are the most expensive basement wall bowing solution but the least invasive and most invisible. No outdoor ground is disturbed and the basement walls can be finished.
Basement Wall Replacement
Basement walls that deflect more than 6 inches typically must be demolished and entirely replaced. While this is the most expensive solution, it's also the most permanent solution.
How to Prevent Bowed Basement Walls
Repairing bowed basement walls isn’t a do-it-yourself job, but preventative measures are. As a homeowner, you can prevent basement walls from bowing after the repairs:
- Fix downspouts and gutters to prevent water from pooling near basement walls.
- Create a robust drainage system with catch basins that divert water far away from the house.
- Build a French drain to catch groundwater.
- Grade soil away from the house.
- Replace expansive soils that reside against basement exteriors will quick-draining sand or pebbles.
- Remove heavy items like machinery or hot tubs (unless the weight is well-distributed on a concrete pad).
When to Call a Professional
Almost all bowed basement walls require the help of professionals to repair or replace them. Foundation repair companies are your best bet, as they specialize in this type of work. Alternatively, you can call a general contractor for help.
Stokes, Becca. "How Much Does Foundation Repair Cost?" Angi, 2021.