Sinking Floors

Sinking Floors

Sinking Floors

sinking floors

if your house is built on a weak foundation, it may result in a sinking foundation, leading to the floor’s sinking.

If you notice any sinking or sagging floors in your home, it could be a sign that the structural integrity of your crawl space is compromised. Over time, those floor joists, which comprise the wooden slat “roof” of your crawl space, may can weaken and cause major structural problems. 

If walking around your house feels like you’re bobbing up and down on a boat in the ocean, then it could be a sign that you’ve got sagging floor joists. Uneven floors are not only harsh on the eyes, but they’re a hazard to the home.

Sagging floors can indicate there’s damaged wood under your flooring, that one of your supports is deteriorating, or that there are problems with the foundations. Here are some other signs that you’ve got issues with your surface and how to fix sagging floor joists before it’s too late.

How Do You Spot a Sinking Floor?

Primarily, when you start noticing the gradual slanting of your house to one side, then your floor is sinking. However, there are a few other silent indicators of sinking floors that our experts say homeowners don’t notice or ignore them. For instance, when you notice your doors or windows being jammed, you should know that you have sinking foundation problems affecting your floor.

Foundation cracks in your basement and on the walls of your living room are still indicators of a sinking wall. Moreover, if you notice water puddles collecting around the base of your home, it also indicates that your house is sinking. Therefore, when you notice things going wrong regarding your house, look into it because it could be an indicator of something worse.

Causes and Solutions for Uneven Floors

Uneven floors are rarely caused by problems with the floor system itself. Instead, it’s often a settling or shifting foundation issue that has impacted the floor system. Floor beams and joists are made from wood that will usually bend or flex rather than crack or break. The same can’t be said for masonry foundations. When soil issues cause a foundation to break, the floors above usually bend.

Since masonry is more likely to break than bend, concrete floors that are uneven are generally cracked and/or broken as well. If your foundation is settling, it may be lifting the concrete floor as the rest of the foundation experiences movement.

There are also times where the slab floor can lift or sink independently of the walls. Concrete slab floors crack and settle when the soils underneath them shrink, settle or wash away. Likewise, a concrete slab will lift, or “heave”, when the soils underneath expand.

How to Inspect Your Home When Your Floors are Sloping

Inspect Support Beams: If your house is built over a basement, first inspect all of the basement support beams and posts where they meet the floor. Be suspicious of wood posts set on dirt floors or wood posts with concrete poured around the post bases. As the posts slowly rot and melt into the floor, the house settles accordingly, bottom to top. As a test, firmly push a metal probe or screwdriver into the post at the floor line. If this area is mushy, punky, or rotten, you may have found your problem.

Also look for floor joists that have been cut improperly to install pipes, wiring, or HVAC ducts.

Look for Insect Damage and Moisture: If you’ve had a chronically damp basement or crawlspace, look for indications of insect damage to structural members. Powderpost beetles leave joists and beams riddled with small holes, carpenter ants are usually apparent at the first sign of warm weather in the spring, and termites usually leave telltale mud tunnels on foundations and posts. Then solve moisture problems around and under the house and repair deteriorated or compromised structural members.

Support posts should not sit on dirt floors, but instead be upgraded to concrete pads with footings that spread the load.

Improper holes and notches from alterations and running service lines are a major source of weakened joists. Generally there should never be any cuts or penetrations in the middle third of any joist, or anywhere along the bottom of the joist. Notches at the end of a joist should not exceed 1/4 of the joist depth. Center notches (B) should not exceed 1/6 of the joist depth. Holes should be a minimum of 2″ in from the top or bottom of the joist, and no larger than 1/3 the depth of the joist.

What Causes the Living Room Floor to Sag?

Now that you have noticed your sagging floor, you may start wondering what might have caused it. Our experts at Ground Up Foundation Repair, point out the following reasons, as the leading causes of a sinking floor.

Poor support

The floor of each of your rooms has long joists, which are supported by a central beam, and the beam is supported by posts underneath. If the underneath posts develop problems such as rots, the beam might not offer sufficient support, making your floor start sagging. Additionally, the underneath posts may be too far apart, hence not supporting the beam, making your floor sink.

Too much space between support columns.

Cinderblock Columns

Can tilt under pressure causing very weak structural support


Settling in the foundation is a possible cause of your sinking floor. If your living room is at the center of your home and is placed on one side, it might be a cause for a sunk in floor.

Excess load

You may have a more massive load in your home than initially intended for your home design. If you have bought a lot of furniture or something more substantial like a piano or maybe you might have added an extra feature on your cabinet, it will add extra weight, which will make your floor to sink.

Excess Of Moisture

Too much moisture in the crawl space causes wood to sink or rot, just like dry firewood overexposed to rain.

When the joists of your floor become old, they weaken and therefore make your floors to sag. Moreover, if they are exposed to high humidity for a long time, they may absorb moisture then rot, which makes them sag.

Poor Footings

Poor footings, or weak soil results in settled columns and cracked or buckling floor joists,


Sinking concrete floors are an indication of building subsidence (when the ground sinks due to movement of underground material).

A building can sink at various points or the collapse can be spread across the entire footprint of the foundation, depending on where the affected ground is and how large an area it is. This can be very serious, and if left untended is likely to worsen, creating further building subsidence and other consequent damage.

What causes subsidence?

There are many different causes of subsidence and various contributing factors. All involve some sort of change in the ground, which, in turn, generates movement of the soil. For example, droughts dry the ground, resulting in the soil (especially clay) contracting. Seismic activity shakes the ground, often resulting in liquefaction which ‘squeezes’ liquid up from the ground. Excavation and construction, even heavy traffic and machinery vibration, can move, displace and alter the condition of the ground.

As well, different types of ground are more affected by different conditions. For example; clay is particularly prone to contracting in drought conditions, gravel and stony grounds can be more affected by nearby excavation, and excess water has a softening effect on dirt. Subsidence can happen over large areas of land or in a small targeted area. It can occur over a lengthy period of time, or can be an immediate reaction to nearby activity or natural events. When ground has been affected, building subsidence is common. Foundations or footings are no longer ably supported, sinking due to weak ground.

Likely causes:

Water flooding the ground Drought drying out soil Washaways from broken pipes (such as water, sewer, stormwater drainage) Poorly compacted fill Liquid, gas or mineral resources being removed from the ground Earthquake and seismic activity Tree roots can suck moisture from the ground Vibrations caused by heavy road traffic or by machinery Absence of an organised footing system – in very old buildings or in buildings with additions or alterations Nearby excavation Heavy loading Deterioration of retaining walls

Sinking Floor Repair

The first step in fixing your sinking floor repair is having it inspected by a professional, from an efficient certified repair company like Ground Up Foundation. Our elite structural engineers will diagnose the foundation problems and tell you precisely what should be done. After the problem diagnosis, our foundation specialist will take over. Our experts use several ways to fix a sinking foundation, and each one of them is efficient for different situations.

Add Reinforcing Metal: Depending upon the conditions, it is possible to strengthen or repair existing framing members, such as floor joists or roof rafters, by adding reinforcing material. Sandwiching the member on either side with plywood is sometimes worthwhile, but the plywood must be installed correctly for greatest strength.

Sistering: A better option is sistering, where identical lumber is bolted to the member.

Sistering with a Flitch Plate: Better still is sistering with a flitch plate, a 1/4″ to 1/2″ piece of steel or plywood. Two flitch plates may also be used to repair localized damage.

Where these repairs are not sufficient, also consider shoring up joists or beams that were cut, drilled, or notched for pipes, wires, or ducts.

Stretch a string across the floor to evaluate the amount of deflection, then use it as a benchmark for improvement when jacking.

One of the good things about floor deflection is that it is repairable. The bad news is that it often takes a long time. The solution to sagging floors, or the damaged sills and joist ends that contribute to them, often involves jacking. A common scenario is to install temporary jack posts and support beams, then permanent posts and beams over new footings. A taut string stretched across the floor will show the amount of deflection and improvement. Posts set on dirt floors should be upgraded to concrete pads with footings. Place wood posts on metal post supports to create a waterproof barrier between the post and the footing.

Jacking must proceed slowly; it took a long time for your floor to sink, so you can’t push it back up quickly without causing cracks and stress in the building. As with other structural repairs, jacking must also be done appropriately. You cannot simply put a screw jack under the lowest spot and start turning. Ideally, someone with experience will assess the problem and set up the posts and any necessary beams. You can then screw the jacks up a turn or two each month. Expect some cracked plaster along the way, and aim not for perfection, but simply stability and improvement. After all, if perfectly level floors and pristine walls were important to us, we wouldn’t live in old houses, would we?

You may want to contact a structural engineer before doing any work as a precaution

High-pressure grouting

This method works by inserting grout into the unstable soil, to improve its composition or raise the structure of your house.

Load-bearing piers

They can be used to raise the foundation of your home while at the same time, stabilizing it. The use of load-bearing piers is exceptionally beneficial in raising your sunk in the floor. This is because they offer a permanent solution to sinking floor problems. Moreover, they are also quite affordable, making them economical to use.

Helical piers

They are mostly used where other piers cannot be used. They are also beneficial because they also provide a permanent solution to your foundation sinking problems. Also, they are efficient, where a high water table is present.

Atlas resistance piers

This uses hydraulic pressure to help push piers into the soil. They depend on the weight of your house, to push the piers down. We use this in places where bedrock is shallow.

This is just a facet of the methods we use in fixing your sinking floor.

Sinking Floor Repair Costs

Have a sagging or sloping floor? This is a clear sign of structural problems. We’ll explain what types of repairs are needed and what they cost.

When your floors slope, ripple, or sag, you know there’s something wrong with the structure of your home. There are a number of causes, and they vary depending on how your home was built.

There is a $800 job minimum for most of the repair types done in this area; in the last 12 months, our customers paid an average of $5900 to repair sloping or sagging floors . This number can be misleading, because there are a wide range of variables that can affect costs.

In this article, we will break down the repair methods and costs associated with each. Our intention is to help you make an informed decision about what you need to repair your home. The first and most significant is the construction type of your floor system. This is because concrete slab floors don’t have the wooden structural elements that come with a basement or crawl space.

FYI: Pricing provided in this article includes both material and labor costs.

The Cost to Repair a Sagging Floor

In the process of covering this topic, we’ve thrown a lot of terms and repair types at you. This is not done to confuse or overwhelm you, but to provide a detailed and thorough examination of the possibilities. While the average repair cost is $5900, there are a wide range of causes, and multiple components to evaluate . This is an area where even experienced DIY fans should defer to the judgment of an experienced and qualified foundation expert. 

The Cost to Fix Sagging Concrete Slab Floors

If the soil under your foundation shifts or erodes, the slab will sink. In most cases, slab jacking is the best and most reliable repair method. Slab jacking is a type of concrete lifting that fills any voids under the slab, then raises the floor back up. The costs for slab jacking begin at $2000, and will increase depending on how much material is needed and how large the area is to complete the repair. For more details on the slab jacking method and how it works, we have an explanatory article here On some occasions, slab jacking is not a good fit. If the soil below your slab is compromised and too soft for several feet, slab jacking is going to be a temporary and insufficient repair. This is because the soft soil will continue to settle, making your floors sink again- sometimes within months of slabjacking. In those instances, the best option is helical piers, because piers are installed to tie into undisturbed soil more than 20 feet below your home.

The price of piers ranges from $1600-$2400 per pier, depending on placement, depth, load requirements, and if they are installed by machine or by hand. For detailed information about helical piers, you can read our companion article about their use and costs . In some cases, both methods are needed.

The Cost to Fix Sagging Floors in Basements and Crawl Spaces

This may be stating the obvious, but all of the structural wood framing in your home is interconnected. This means that one component may not be the only one at fault. In our experience we’ve found that multiple parts of the flooring system are usually affected. The direction or type of sagging floor usually highlights the area of greatest concern, which is how we explore the types of repairs below.

multiple causes that account for your sagging floor , but you should know that water and humidity often play a role. When you are planning to make repairs to your wooden framing system, keep in mind these may not be the only costs to consider.

Water around a foundation can cause settling or sinking; if you suspect this is an issue, we have a detailed guide to foundation repairs for you. You may need treatment for mold to restore good air quality to your home. You may also need to add a water drainage system to prevent the problem from recurring in the future- not only in the repaired sections, but throughout the basement or crawl space for prevention.

Sill Plate Repairs

If your floor is sloping towards an outside wall and the foundation has not moved, this indicates that your sill plate is compromised. The sill plate is the piece directly on top of your concrete foundation, and it has to be replaced if faulty. To replace the sill plate, jacks are installed to temporarily hold up the floor joists, until the damage sill is removed and replaced. Costs for sill plate repairs are $100-$110 per linear foot.

Floor Joist Repairs

When the floor drops, dips or slopes it often means you have failing joists. Because the joists rest on the sill plate, water damage often spreads from sill plate to joist. Another common issue – especially in older homes- is notched joists. Older homes often have updated plumbing or HVAC systems installed; contractors sometimes cut sections out of joists to make room for new ductwork or pipes.

These notches weaken the joists and cause them to crack, split, or fail. Sagging joists need to be sistered to be repaired; removing the joists entirely would cause damage to the subfloor, and possibly to your flooring itself. When a joist is sistered, a healthy board is run parallel and attached to the faulty one, to transfer the load. Sistering floor joists costs $12-$14 per foot.

Band Board or Rim Joist Repairs

Band boards- also called band joists or rim joists- are the wooden piece that sits on top of the sill plate. It protects the ends of the floor joists and helps support your home’s outside walls. Like the sill plate, the band board can be exposed directly to the outside air which increases the odds of it being damaged by humidity. Like floor joists, the best method for repairing band board is by sistering. Sistering band board or rim joists is $40-45 per foot.

Center Beam Repairs

The most common complaint we receive is that the floor sags towards the middle of the home. This indicates that the center beam is failing in some way. In some instances, there are shims that have compressed and need to be replaced. We use steel shims that will not compress and increase the surface of the bearing load. Installing or replacing shims is $105 per column.

If any of the support columns under the center beam have failed and need to be replaced, adjustable steel jacks can be installed. Likewise, if there are an insufficient number of supports currently installed, additional jacks can be added to better divide the load and increase the bearing area. Additional steel jack installations cost between $190-210.

For repairs with adjustable jacks, please be aware that the floors will not immediately return to level. Jack adjustments are done in small increments over time; attempting to expedite this process can cause damage to your home. 

If the center beam has cracked, split, or failed entirely, the best option is to replace it with a steel beam. Much like replacing a sill plate, jacks are used to temporarily hold the joists in place. Once those are secured, the damaged wood is removed and replaced with steel. Beam replacement is $260-$275 per foot , depending on the number (if any) of additional supports that are needed.

Support Column Repairs

If your floor sags in one specific area, this is possibly due to notched joists or beams. (Please refer to the earlier section on Floor Joist Repairs for more information.) If this is the case, sister joists or sections of steel beam can be installed to remedy the issue.

Frequently, a sagging floor in a localized area is caused by a damaged support column. If a wooden or concrete support is weakening or failing, it can be replaced by one or more jacks. Steel jack installations cost between $525-575.

Sinking Floor As A Typical Issue In Old Houses

One of the most common complaints of old-house owners is sagging floors. In my own house, for example, every floor pitches toward the center stairwell. Although generally only an annoyance, sagging floors can be an indication of worsening problems. 

Depending upon the conditions, it is possible to strengthen or repair existing framing members, such as floor joists or roof rafters, by adding reinforcing material.

What Causes Sagging Floors in Older Homes

Typically, floors settle near the center of the house because the perimeter walls are constructed over a sound, deep foundation and settle very little. Major support beams within this perimeter, though, are often supported by makeshift posts.

Slab Floors Sinking Independently Of The Walls

Slab floors that are sinking independently of the walls can be repaired with a slab pier system . These piers are placed in cored holes in the floor, extending down to competent soils to hold your floor in place. They can even be used to lift a slab back to its original, level position.

If the floor is cracked and uneven because of foundation settlement, then your contractor will recommend either foundation push piers helical piers to stabilize the entire foundation. Foundation piers can also be used to lift the foundation to its original position in some cases.

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BY M. Kogan

Hello, I am Marcio. I am an architect and designer, alma mater is Mackenzie. Retired in theory, but an architect never retires completely. Along with architectural projects, I am a filmmaker and have completed some short documentaries. Filmmaking and design are my passions. In HomeQN I write about home decoration and foundations. The goal is to teach homeowners to DYI as much as possible, and when this is not possible, enable them through knowledge, to evaluate service quotations and choose the best service technicians.

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