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Sinking house cracks (C) Daniel FriedmanSinking Buildings & Floors
Causes of Building Settlement

Sinking or settling buildings:

This page explains causes of building settlement or sinking (distinct from sinkholes), and gives building and site inspection advice useful in identifying areas where there is an increased risk of building settlement.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Causes of Soil Subsidence & Building Movement Not Due to Sinkholes

Stormwater drainage sinkhole in Pennsylvania - PA DCNR

The bare minimum that a property owner needs to know about sinkholes or any other sudden subsidence of soils at a property is that these conditions might be very dangerous.

Someone falling into a sink hole or into a collapsing septic tank could be seriously injured or even die.

If a suspicious hole, subsidence, or depression appears at a property the owner should rope off and prevent access to the area to prevent anyone from falling into the opening, and then should seek prompt assistance from a qualified expert, geotechnical engineer, septic contractor, excavator, or the like.

The photograph (above-left) of a sinkhole opening in a residential yard in Pennsylvania is from Kochanov, W.E. and illustrates the child hazard or even adult hazard that storm water drainage sinkholes can form.

Kochanov, W.E. lists and we elaborate and expand here a variety of subsidences that are not caused by sinkholes, followed by examples of sinking houses not caused by sinkholes, and examples of cesspool or septic system collapses.

Floor collapse pulls away wood post from ceiling - Northridge CA earthquake (C) Daniel Friedman ... Floor collapse pulls away wood post from ceiling - Northridge CA earthquake (C) Daniel Friedman

Understanding the cause of a sinkhole assists in knowing what to expect in the future and in planning for building or sink hole repairs. An important key to identifying a sinkhole area is to consider the location of carbonate bedrock.

Watch out: significant building movement may be caused by a variety of problems other than sinkholes.

Some of these are equally dangerous, and expert evaluation is important. Consult with a structural engineer who is specifically familiar with building and foundation movement and failures.

Examples of conditions that can raise serious, urgent concerns for safety and risk of sudden, catastrophic building collapse include at least the following:

Readers concerned about soil subsidence or sinkholes should see SINKHOLES - IMMEDIATE SAFETY ACTIONS, and also

see FOUNDATION CRACKS & DAMAGE GUIDE

and CESSPOOL SAFETY WARNINGS.

Additional septic system safety warnings are

at SEPTIC & CESSPOOL SAFETY

. Readers concerned about diagnosing building movement from other causes should read this article, and also

see SITE FACTORS AFFECTING FOUNDATIONS

and FOUNDATION DIAGNOSIS & REPAIR.

If your concern is cracking, settlement, or heaving of a concrete floor slab,

see CONCRETE SLAB CRACK EVALUATION.

Sinking Houses Not Caused by Sinkholes

Fairbanks house settlement (C) Daniel FriedmanCase Report: Sinking House in Fairbanks Alaska

An InspectAPedia.com reader has shared photographs of a sinking house in Fairbanks, along with reports of investigation about the probable cause and remedy of this possibly dangerous condition. From examination of the owners' photographs it appeared that the home was constructed on piers set on permafrost.

The occupants of the home observed an increasing frequency and degree of movement in a new home whose structure was unfinished, including

The house was built by my husband. The walls are 2x6. His idea is to lift the house and build a floor under it. It was built on a concrete slab in 2005. We had Soils Alaska come out a few years ago and check out the grounds. They bored two holes and gave us a report.

They did not seem too concerned about the settling. I am concerned because I am seeing movement everyday. Can you tell me the signs to be really worried and to get out of the house? Our neighbor has a work shop that started moving and he found a big six foot hole in the center. - K.R. Fairbanks AK

Signs of house movement (C) Daniel Friedman ... Signs of house movement (C) Daniel Friedman

The owners were concerned about a possible sinkhole under the house - as sinkholes have been reported in Alaska. But another possible explanation was an effect of global warming and loss of stable permafrost under the building.

It was not reasonable to attempt to "diagnose" the cause of movement in this structure by remote consulting - onsite investigation by an expert, probably a geotechnical engineer, was needed.

Reading the owners' description of house movement and examining their photographs, it was apparent that there was significant ongoing structural movement and that the building may be unsafe.

Here was our advice on investigating this moving structure:

Building Movement Analysis Divides Into These 3 Main Categories

  1. Amount & rate of building movement: What is the present extent (how much so far) and rate (how fast) of movement and does either of those make the building unsafe

    – for example, if movement has moved framing such that framing connections are insecure a floor could collapse leading to serious injury, or if there are sinkholes or a sinkhole from melting permafrost or other cause, a sudden foundation collapse could be dangerous as well. If you are really seeing movement every day that sounds like a significant safety concern.
  2. What is the cause of building movement – is it poor framing connections, improper design, improper site preparation below the foundation, or an innate site problem like a sinkhole?
  3. Structural repair need & urgency: Based on the above, what repairs are needed, and at what urgency and with what alternatives. In cases of unstable buildings where there is a threat of sudden collapse, it may be necessary to immediately evacuate the structure and protect its surrounding area, notifying the appropriate local authorities.

When we understand the cause of movement that will determine what repair actions are needed and will also help understand the level of risk.

Call a soils test engineer (a geotechnical engineering firm had previously done some analysis at this property) as well as a foundation inspector or structural engineer familiar with building failures in your area, to answer the questions posed above as well as to tell us if there are other critical questions to be asked.

See CONCRETE SLAB CRACK EVALUATION for more detailed guidance on slab crack diagnosis and repair.

See also ARCTIC SINKHOLES

Case Report: Basement Slab Heaving, Residential Home in Edmonton Canada

Cracking floor slab sketch (C) Daniel FriedmanThe following reader correspondence discusses the observation, diagnosis, and repair of a cracking, heaving, and settling basement floor slab in Edmonton in 2010.

Cracking Basement Slab Sketch & Complaint

I've been reading about foundations and cement slabs on your website and would like to know if you might possibly have some business contacts here in Edmonton, Alberta, Canada I may contact regarding a problem we're having with the basement floor in our not quite four-year old home.

Ultimately, I'm hoping to find someone qualified in the city I reside in and since your website is the only one thus far that actually addresses such issues as cement slabs, I'm hoping you may know someone.

We've had the City of Edmonton, the homebuilder, as well as a company specializing in basement repairs all come in to provide their opinion as to what's happening. Regrettably, not only do none of them appear to agree on what the cause is, none of them agree on how best to rectify the situation.

Further, the structural engineer I contacted informed me that he can perform a “visual inspection” of the existing slab and provide his assessment as well as recommendations for a fee.

He has however, cautioned me that he can’t see what’s happening below the slab and has no first hand knowledge as to how the subsoil was prepared, the water table, etc.

Since I thought that residential structural engineers would have expertise in this regard and he’s indicating somewhat to the contrary, I question if he will be able to help us rectify the situation we find ourselves in.

I am in a bi-level house that is not quite four years old. All homes in our city are required to have sump pumps.

When we moved in, the basement floor had a few hairline cracks in it. Over time the cracks became more pronounced and then during this past year we've noticed that a few of the cracks have developed separations of approximately 1/8" in width and are now intersecting. In addition, where some of the cracks intersect, the concrete slab appears to have almost lifted or risen at the intersection point. I say “appears to have lifted” because the slab along the perimeter around these intersecting cracks is lower than the point of intersection.

When they first appeared, the perimeter didn’t seem lower to us, nor did the cracks intersect.

I contacted our builder to request the results of the Soil Bearing Certificate for our lot. It indicates that the engineering firm probed the soil up to 36" below the footing level and found some evidence that 8-10" of soil at footing level was disturbed from its original condition.

As such, they required that piles be placed under the footings for additional support in the event that the disturbed area settle in the future. I asked if there was any indication of water and was told that while there wasn’t, water tables change all the time.

I'm lost as to if its a soil issue, a water issue, both, or something else altogether different. A neighbour at the opposite end of our cul de sac has had so many problems with his sump pump and water that even the walls in his house have developed cracks, the drywall shifted as well as problems with the trusses.

Right now, I'm wondering if I should just go further into debt and have the whole basement floor removed somehow and redone, though I don't know how since a year ago we had it framed and drywalled. - M.S. Edmonton, Alberta Canada

Some Diagnostic Questions for This Slab Cracking Problem - DF

More Cracking Slab Diagnostic Information from the Homeowner

We have provided a very rough sketch of our basement slab. All cracks are 1/8" or more in width unless otherwise indicated. With respect to the questions you've asked, I know for certain that:

Diagnostic Comments on the Cracking Slab Observations Above - DF

So this basement floor slab is not structural, nor are the cracks a structural threat unless someone failed to make separate piers below any columns;

Your sketch shows that cracks in the slab appear related to not only one end of the building, but points in the slab where there are penetrations.

Often these patterns suggest that there was uneven compacting of fill below a floor, perhaps more of a water problem in that area, and that in a stressed floor slab cracks often originate at stress points or points of uneven structural unity, such as at an outside corner in the foundation wall footprint or at openings cut through the floor for pits such as a sump pit or a drain.

Generally basement floor slab crack patterns could be due to concrete slab shrinkage or floor slab settlement - but shrinkage occurs early in the slab life; settlement can occur later; Shrinkage cracks in a slab are discontinuous; settlement cracks are not, as the slab is actually breaking;

Shrinkage also won't produce a crack with the slab at different heights on either side of the crack;

So it sounds more as if you have soil settlement under the slab, or if the home were left un-heated, frost heaves.

If we've got settlement, sumps can contribute to settlement by undermining a slab (or worse, a footing or foundation wall) by slowly removing fine soil along with water that it pumps from under the slab (water should not be there - a drainage problem), but more likely this slab was also poured on loose, poorly-compacted fill.

Often fill is dumped at one end of a foundation and then leveled, sometimes just by hand, by a low grade worker. [This was my - DJF - first job in construction]. In those cases perhaps no one compacts the soil, it is just raked roughly flat before the slab is poured.

Furthermore, if the original grade was sloped and fill is being used to level up the foundation interior before the basement slab is poured, then there will be more total fill at one end of the floor than the other, making settlement and slab cracking more likely at that end.

The fix for this floor cracking can be costly if you have to break up, compact soil, and re pour; most people wait on that; there's also mud jacking - pumping hydraulic concrete mix under the slab, but you'd need to evaluate the soil and conditions under there first, and mud-jacking is not very appropriate if the floor slab has cracked and broken into many pieces. Mud-jacking works best when the slab is mostly or entirely intact.

Re "one company believes all our problems due to sump pit being too shallow and not cutting in often enough " - that is nonsense; a deeper pit makes the sump cycle less often, sure, but the same volume of water gets pumped out;Moving out more water or moving it out faster doesn't fix a settlement problem, it probably speeds it up; unless you were intercepting water and keeping it from under the slab in the first place;

I think you are going to need to make a hole or two, either by drilling or by breaking up the slab - I'd do it in the worst-cracked area - and see what we've got there. Or start breaking out the slab enough to see what is the condition of soil below the area of settlement.

If it's not a structural threat it's not so urgent; don't trip on the cracks;

See CONCRETE SLAB CRACK EVALUATION for more detailed guidance on slab crack diagnosis and repair.

Update on the Edmonton Floor Slab Cracking & Settlement: Diagnosis & Repair Steps Taken by the Owner

An Edmonton Canada property owner was kind enough to provide us with this update in May 2010:

Believe it or not, the more we looked into our heaving floor issue, we found that we were told by several individuals that Edmonton has actually been considered as being in drought-like conditions over the past three years?! As of this April our house is four years old.

One of the engineering firms we contacted suggested drilling holes in the slab and observing the water table under the slab but lost our confidence when they indicated that in the end, they’d still only be providing us with their educated guess as to what was happening

and after I asked what good it would even be to provide me with a “certified” report (as you know, engineers aren’t the cheap route, either), they indicated that water tables can change at any time, so this simply made us feel we’d be no further ahead than when we started.

Although it wasn’t our first choice, in March we had someone in to break up, compact soil, and re pour the north facing portion of the slab where it had been heaving.

Prior to starting this job, the company we enlisted even told us they wouldn’t be surprised if we had some cracked pipes

– they indicated they were finding a lot of this in new homes with problems similar to ours. When they jack hammered the floor they found the soil was damper than it should be, but there was no standing water and no cracked pipes.

They took out the sump pit, compacted the soil, drilled holes into the sump pit, put crushed rock in around the pit and ran weeping tile all along the north perimeter of the house where the slab had also been heaving and then they repoured.

Quite honestly, we still don’t know if we did the “right” thing but after all the people we had come by to look at our floor and provide their opinions, we somehow got the feeling that none of them really have the answer as to what’s happening.

Of course our hope is that this situation is rectified. However, yet another neighbour three doors down from us in the cul-de-sac is also experiencing horrible problems with his floor and foundation. And, just like the others in the area with issues such as his, they all appear to be two-story homes, while ours is a bi-level.

As a home owner I find it quite shocking and disheartening to learn that it’s the year 2010 and the house building doesn’t appear to have progressed very far in terms of technology, etc. yet this is the largest purchase a person will ever make!

Follow-up comments on the Heaving Floor Slab Case - DF

The observation that on breaking up the slab for inspection the contractor found that soil was damper than it should be suggests that either drought was not a direct cause in the floor settlement, or a cycling of dry and wet conditions was at fault, similar to the expansive clay soil problem that occurs below homes in other parts of North America such as areas of Colorado.

Case Report on Sinking Houses in New York State

In the Wappingers Falls, New York home shown in these photographs taken in 1999, significant ongoing cracking and movement was apparent in the building interior, including

Sinking house cracks (C) Daniel Friedman ... Sinking house cracks (C) Daniel Friedman

Further investigation into the history of the site indicated a condition that may have been the cause of this movement: the home had been constructed on poorly compacted fill over what had been a stream bed.

Sinking house cracks (C) Daniel Friedman ... Sinking house cracks (C) Daniel Friedman

A second Hyde Park, New York house settlement case in the 1980's (est) was traced to construction of the home on what had been a landfill. By bad luck, a portion of the home's foundation was constructed on fill while the other half sat on more sound soils, leading to significant differential settlement. Small "sinkholes" that occur in landfills as buried trash, tree stumps, or debris rot and settle can nonetheless be very dangerous, especially to children.

Repairs of that sinking home included an extravagant installation of a custom engineered steel frame and supporting piers.

Depending on the cause of house or foundation settlement, other more economical repair methods may be suitable such as the use of helical piers or mud-jacking (pumping grout below a settling concrete slab or walk or even a foundation wall).

Cesspool & Septic System Collapse Hazards

Sinkhole or drywell collapse in New York (C) Daniel FriedmanA question about sudden back yard cave in leads to warning of a cesspool collapse that can be fatal.

Earlier this evening, after a day of rainfall, our backyard caved in. Currently there is a hole in the ground about 12x10ft and 6-7 feet in depth. After the initial collapse, there was some growth in the diameter but that appears to have stabilized. The closest edge is about 6-7 feet away from the actual house.

[Photo at left shows the New York "sinkhole".]

See SINKHOLES in NEW YORK for details of this case and our advice on what to do about this sudden yard collapse in New York.

Watch out:  Immediately rope off the area of any soil subsidence or suspected old septic tank or cesspool area, and mark it plainly as unsafe so that a wandering neighbor, adult or child, does not go near nor fall into this hole. It could be quite dangerous.

See CESSPOOL SAFETY WARNINGS for examples of potentially fatal cesspool collapse hazards.

 




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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2019-11-07 by Don

We have a property that has cracks in the wall paint, separation at the corners of rooms and wood trim. Floors show signs of not being level. The property is located in Lone Tree Colorado 80124.

On 2019-03-14 by Major639

This article helps a lot, thank you! This February 2019 in Garrison, MN, a garage on the property under contract for deed we signed in September 2018 collapsed suddenly.

This, roughly 70' x 40' "pole barn", is/was the best and most finished of them all and were told it had an industrial quality floor (used to have a car lift for restoration projects), a floor drain with unknown drain location, 2x6 insulated walls, drywall (unfinished but complete), ceiling foam board with blown insulation above, roughly 15'x20' garage door (this was smaller than the original and the framing and garage door opener hangers were clearly redone),

two visible fireplace/heater flues exiting roof and side wall, covered with a metal roof with what appeared sufficient pitch especially since it's metal. No really noticeable signs of water damage aside condensation where drywall wasn't taped, but there was a crack across the entire front of garage about 3 feet in, I'm from Colorado so didn't think to much about that.

The property backs up to our DNR Marsh land lot and there is about a 25' drop to the water level, running water. It's slopped steady from back of garage with about a 5' drop to the water.

Recently discovered, was not disclosed before, is 1 of possibly two septic tank systems about 20' directly behind, dead center, of the garage in question. First, I'm pretty sure it's illegal distance away, installed septic on hill leading to and less than 50' from State DNR Marsh land...

Second we never found it until before first snow once all the raspberries and other foliage disappeared and we found trash buried and exposed all over that hill, also there is a fence running from center of garage down to the water and trash piles around it with blackout netting as to hide things like trash, 100lb propane tank is one. After moving a couple boards I found the pump pipe under and broken off.

Also looking in you can see the pipe is bent downward towards water and only about a foot and a half deep to inlet from house?? So after moving fence panels, wood and how ever many years of natural mulch, we found the the corner of the tank lid exposed, not just exposed but intentionally broken open at corner under the lid.

I say intentional because hole was proportioned, Sledge, and pliers were still there where the thin mesh metal, used to reinforce the concrete box, was cut clean. Huge huge huge problem, not just our garage but now polluting State natural resource wet land that feeds one of the largest lakes. S

o DNR, state health, EPA and who knows how many other agencies, fines, jail, property loss, and clean up fees will come with this issue, clearly intentionally created years ago.

So to finish, garage collapsed, seller was already in breach of contract for a, can you guess, failure to get proper sewer/septic inspection of compliance prior to transfer of said property. Well county doesn't have to follow their own laws according to them and can transfer title and Torrens prior to inspection regardless clarity of statues.

So many things wrong but ground is now apparent it's very gravely and unstable, very heavy structure built improperly next to the hill above septic leaking, and a garage South about 10' away and built at a lower grade level and North side a 40'x30' green house about same distance away but discovered exposed french drain along garage on green house side, can't find exit.

Between the South walls was raspberries with a path down middle and random 4"drain pipe coming out level with ground and no lid??? Also no access to pump tank so makes sense why one desperate may open it.

Also it's clear to see the sewer was dug up recently, probably to repair a break from shifting because it's the only flat path like section on the hill and I was a plumber so it's obvious. Garage appears to have separated from front, it's still standing and explained the crack, but the back wall feel down the hill and in process roof collapsed in while side walls appear to have just fell outwards.

No signs of water damage, actually want to auction off the structures knowing that the wood is clearly good. I feel it's pretty clear cut cause of failure, at the least it was sliding/shifting/sinking in the back down the hill (that's also where the lift was placed when it was there).

I have a $35K+ Mitsubishi Evo show/race car sitting under that that just got hit with ice, blowing the turbo in -33° ambient temp, tow truck ripped front bumper, and was waiting tow to the shop that put 5K into the motor 4 days prior to the only damage

. That's a love ton of claims in a short time and I'm just grateful no one was working in there during the collapse. To get to my question I guess is am I on the right track with the evidence we have accumulated, without touching anything yet, who would be the best expert(s) to call for determining causation of failure?

One last thing, I talked to county building department and no records of permits and supposedly wasn't required pre 2014 but in what was left behind that's not the case because we have permits from the original owners (company) of many jobs including his home dating back to the 80's... What the f&#@?

Thank you if you did read this and any advice would be very appreciated as the snow is finally melting but now raining on snow so I can't see this getting better for any other structures on the property.

On 2018-05-17 - by (mod) -

John

To fix a settling building foundation you need an on-site assessment by an experienced mason or a civil or structural engineer who is familiar with residential masonry foundation damage diagnosis and repair.

No "fix" can be proposed before we know

1. the cause of the foundation movement

2. the extent of movement that has occurred

3. the effect of that movement on the rest of the structure

Repair may range from doing nothing to addressing an outside roof runoff or surface drainage issue, to crack patching to slab jacking or insertion of a helical pier or more piers, to excavation and reconstruction of the foundation wall.

On 2018-05-17 by John

The brick foundation at the southwest corner of my house has sunk making the floors uneven. The house is more than 100 years old. How can I fix it?

On 2017-04-21 - by (mod) -

Slavica

If the slab hasn't moved in the last 17 years, surely your engineer would agree that if you keep water away from the area (avoiding settlement) and seal the crack that'd be sufficient?

If you needed to stabilize, lift, or repair the slab you might want to

search InspectApedia for our articles on HELICAL PIERS for foundation and slab repairs, and also to look at SLAB JACKING or MUD JACKING for settled slab repairs (less suitable I suspect for your case)

On 2017-04-21 by Slavica-Louise

We built a commercial buildingin 1984, it is only 30x50 ft and it is on a concrete slab. I noticed a few years ago a crack in the north west corner and it hasn't gotten worse since the year 2000.

There is a really old building next to us that has no concrete foundation and their roof is 1 ft lower on the side where it meets our building.

The roof isn't leaking and everything is looked after so we don't know why that corner of our building is sinking. When they were redoing our road in front of the building I talked to an engineer and she showed me the sizes of gravel in the hole where they were putting new pipes for the city.

She says that there is sand, small gravel, large gravel, boulders of all sizes and the soil is simply terrible for stability. There are other commercial buildings that are almost 100 years old and sank in 1 ft just like the building next to us.

When I put a round bead on the staff room counter it rolls toward the west, so the west side of the building is sinking for sure.
Is there a way that could be fixed ?

I guess if the ground is bad here there isn't much one can do. It could be too costly and if it sinks that slow, it wont get much worse in my lifetime.

On 2016-10-27 - by (mod) -

Interesting, Tim. Thank you for the comment.

I've added your remarks to FOUNDATION REPAIR METHODS and would welcome further comments or suggestions.

I'd like to see more information and perhaps add an article on this approach. If you're interested in helping out you can use our page top or bottom CONTACT link to send along suggestions.

Below I also post additional remarks from Tim that were blocked by our Comments Box code that doesn't accept URLs.

I would like to start with Fairbanks Alaska, this is one of the most active permafrost regions in Alaska and the movement can destroy a building (See CCHRC)

Multipoint Foundations have over 800 foundations in Alaska (Fairbanks was one of the first locations back in 1985 that had a MPF install and monitored by the University of Fairbanks)Your home is moving due to discontinuous permafrost and the heaving that is caused in the freeze/thaw cycles ...

On 2016-10-26 by Tim at Multipoint Foundations

Vacant lot in PA
With the Multipoint foundation you can have a steel frame floating foundation MPF that acts as a concrete raft slab but at only 10 lbs./ft2

so you are not overloading the already poor bearing conditions with a concrete slab at 200-300 lbs./ft2. The frame acts as a "Snowshoe" and the load of the building is spread out evenly over the site.

The system has incredible bridging capacity which allows for loss of bearing in one location to be transferred to another set of feet or bearing plates. This technology is over 30 years old and has been used, without failure, in the harshest environments in the world.

 


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