House has "sunk" towards one corner since construction in 1966

[kgold]

A house that I purchased up may need some foundation work. I'll start off by saying that I will be bringing in a specialized consultant however in the meantime I'd like to learn more about this kind of issue.

The house is a 1966 bi-level (raised bungalow) in central Canada. It has not been updated or taken care of much since the previous owner acquired the house in 1973. Specifically, the conditions of the eaves-troughs and downspouts are abysmal and it is reasonable to assume that drainage has been poor and lots of water may have pooled in the back left corner for 10+ years. Using an automatic laser level, I determined the house is sitting at 0 inches in the front right corner; -2 in the back right, -1.5 in the front left, and -4 in the back left. As this is a raised bungalow, the footings are only about 4' down and this puts them close to the frost line at this location.

All the obvious signs of settlement are present however they are far less dramatic than you'd expect for such a high level of sinkage. There is minor drywall cracking around some windows and doors. The concrete slab has cracked such that it fell with the footing in the back left corner. About 8' from the front wall, the slab's first cracks are present and from there it slopes gradually to the low corner.

The foundation wall does have a crack in it along the left-side wall however it is less than 1/8th inch wide. It appears as if the entire foundation rocked down and back towards that corner over the years, and brought the upper level of the house with it.

Ideally I would like to level the house but it may not be worth it if I could safely say it is no longer sinking. I think the first place to start will be with a soils/structural consultant however I'd appreciate it anyone has any ideas or input on what could be going on here. I think it has to do with the drainage issue and perhaps a soil issue (improper digging/backfill which was not compacted).

Are there things to look for that will indicate if movement has stopped? What would be the best way to resolve this issue? Underpinning comes to mind. The soil appears to be OK under other houses nearby as they have not moved in the same manner. Another option we've considered (if we can safely say it is no longer moving) is to jack up the house and shim it on top of the foundation.

Again I appreciate your input and if there is any other information you need to comment, please ask as I am hoping for several perspectives.

 

[cvg]

first - improve the drainage situation. ground should slope away from the building, downspouts should discharge away from the foundation, trees and vegetation should be held back away from the foundation

second - determine what the near surface foundation soils are (granular, clay, silt, etc), by digging pits, auger or other methods. try to determine depth to bedrock and depth of water table as well if it is shallow. also determine the actual depth of the footings. Your expert will need all this information.

I would think that if the building has settled only a few inches in 50 years it is likely stable. But the only way to determine movement is monitoring. to do this you could set up a survey benchmark and then measure the elevation of the foundation at each corner.

 

[oldestguy]

Central Canada. Are you in the Lake Aqassiz area? That's a former large glacial lake area extending over a large area. If so, maybe your are experiencing settlement due to shrinkage of clay due to drying caused by trees taking the water. Before doing any underpinning, check that out. On the contrary, have other parts of the site been raised instead by frost action?

 

[kgold]

I am inclined to agree that it is stable (perhaps just being optimistic); the largest drywall crack was crudely mudded over and then later covered with wallpaper from the 60's or 70's.

I am indeed in the Lake Agassiz area (Winnipeg MB). Some soil testing we did during a project at work revealed that near surface soil (7km from the house) is clay: silty, trace medium sand, dark brown-grey, moist, firm to stiff. I don't know how consistent this layer would be across the region. I expect the water table is not shallow and is below the footings.

Your point on shrinkage is interesting as there is a large tree on that side of the lot. However, it is about 30' away from that edge of the foundation. Could this theory contradict the fact that the drainage issues stole away too much soil? Or could the two conditions combine to have caused the settling depth of 4 inches?

 

[msquared48]

Depending on the recommendations of the Geotech, you might consider the use of 2" diameter pin pile to level the structure if further settlement is still a possibility.

Mike McCann
MMC Engineering

 

[oldestguy]

Trees draw water from where ever they can. A full grown elm is said to require 50 gallons a day or more to live. Certainly all area within the "drip area" is a likely place for drying from them and to deep depths (to 15 feet easily). This is a common problem in many areas that are lake laid sediments and your area is plagued with them. Are there any cracks in the soil visible?

Treatment is easy. Remove the tree. We have found in some cases that watering the ground near the building and leaving the tree brings the building back up to where it was built. In one case for an older high school auditorium it even closed up all the wall cracks on the side toward the trees. I don't know of one place where watering was done that did not fix it.

If the soil tests show that a stiff to hard clay is common, I'd bet on the shrinkage as the problem. Underpinning a hard clay supporting soil??? I've seen that done, to no avail.

 

[kgold]

The tree theory sounds great... I'm hopeful however I think this tree may be too far away to have had this effect. Especially given that the whole house "rolled" back into this corner about the front right corner (the 0 datum). The yard does have a significant dip in it between the patio blocks (near the dropped corner) and the tree, however there are no cracks and so it'll probably take some testing to determine the moisture content before I could be certain. Until that point, correct me if I'm mistaken but its probably a bad idea to water the ground in this area when the drainage issue is still valid. One other possibility is that there may previously have been a large tree in much closer proximity to this corner.

Mike, I ran a few searches for small pin piles and there isn't much coming up in my area. Are you referring to the "push pier" type system? Does anyone have experience with underpinning in this manner or in general? I'm curious to know the cost and if much can be offset if the digging is performed by others.

If the house has stabilized I'm inclined to simply jack up that corner a couple inches off the foundation. I think this can be done with 3 10-ton bottle jacks about this corner, an additional beam running front to back (perp. to the joists) and a couple extra teleposts. I would separate the vertical 2x4 studs in the pony wall from the "footer" 2x4 and replace them with new boards cut to the appropriate lengths. The raised height change will decrease as you move away from this lower corner, so the 2x4's will be all slightly different lengths. I'll have to cut the stucco from the parging prior to jacking.

Are there any issues that could still cause relatively rapid sinking of this corner? Drainage will be fixed and the tree will be cut down by half at least (for other reasons). The cracks in the slab appear to be quite old. I took a closer look at the crack on the left wall and its actually a hairline crack that is entirely vertical (it is covered by cement in a "fix" by the previous owner so I assumed it was greater in thickness). Interestingly, where this vertical crack meets the slab, a larger crack spans outward within the slab perpendicular the foundation wall.

Thank you all for your help.

 

[oldestguy]

For information on past jobs. The high school I mentioned also had a gymnasium with a tree off the corner. Elevations taken on the gym floor revealed circular contours, centered at the tree, all the way across the room. I don't know what they did about the gym other than cutting down the tree there.

Another job was a nursing home where I happened to visit and saw the vacant rooms because of damage. The manager was getting a geotech firm to see what's wrong. I suggested the tree outside the rooms was doing the damage and gave him a list of tests his geotech firm should run. I told of some watering success elsewhere. A year later I was visiting again and asked what the geotech firm did. He replied, he did not hire them, but instead watered the tree. The rooms came back up and were occupied.

In these cases, you need to keep the watering going in dry weather if the tree is to stay.

With any jacking up job, etc., be aware that with a change of season, your support ground may come back up and bring along any jacks or geopiers resting over that affected soil. Then you reversed the elevations, maybe.

First off you need to know your soil moisture situation and the Atterberg limits, as a minimum. They usually will reveal how nasty the soil is there for shrink -swell potential. That info will help you decide what to do.

As to 30 feet from a tree, I suspect that is well within the "zone of influence".

 

[oldestguy]

Look what I found. My old files had this publication as a reference and now it is on the Internet. Deals with your area.

http://archive.nrc-cnrc.gc.ca/eng/ibp/irc/cbd/building-digest-184.html

 

[BigH]

The Bozozuk paper referenced from Geotechnique is a good one - with respect to trees (just passing on information). If one is interested in this google a few keys words. UK has some good references on trees and their effect.

 

[oldestguy]

BigH:

In the references also there is the name W.G. Holtz. We (where I once worked) hired him due to a bad swelling problem. He told of first learning the hard way. With the US Bureau of Reclamation and the many canals they built in the SW US, He and his buddy recall sitting on the bank of a canal and seeing all the paving buckled and failing and wondering why. With his own house in Denver, each winter he adjusted basement column poles to allow for the basement floor to lower in winter and later rise in summer.

 

[motorbiketocrank]

By looking over your yard and the surrounding area, can you tell if there was any substantial grading done during the original construction? Often, fill placed to level the lot can cause the settlement (not just due to poor compaction of the fill but because the weight of the fill causes settlement below it). If this were the case, there's a good chance the major settlement would be complete.

 

[kgold]

OG - it is definitely common in this region to seasonally adjust teleposts.

I can't tell if grading was done except for a dip in the middle of the backyard with the property line along the back being higher, as well as the grade sloping away from the house. I should also mention that this corner has a small (4 x 8) concrete pad on it that was poured when the house was new as a landing for the stairs coming down from the back door. Could this have had an effect on the soil conditions around the footing below?

While 4 inches is significant, none of my guests have made comments on it and it is not until I point out the issue that they notice. For this reason, I think if I were selling the property the viewers wouldn't be too hung up on it. But I would like to have something legitimate that states the likely causes of the settlement and that is has finished in case their home inspector notices and voices a concern.

Back to the tree theory... I found out that there used to be a massive tree at the front of the house on the LHS. This front corner is only about -1.5 but is it possible that the tree influence was more destructive at the back corner?

 

[oldestguy]

Not seeing the situation, I suspect that an earlier tree situation may have stabilized or weather conditions were different. I hesitate to recommend any watering or other treatment of "settled" areas, not knowing more details.

If removal of the tree near the worst "shrinkage" is done, you might wish to do a little gradual watering to speed along the "stabilizing". Don't get too pushy. It isn't always "If a little is good, a lot is better".

The waterings that I know of were in trenches next to the building, leaving the tree to fare as it can without help.

GEOBLD brings up another possibility. Many times where there has been a "failure" of some sort, it often is found to be caused by a combination of factors and not just one. Remove one of them and a much less tendency to fail, etc. At time of construction maybe a tree was removed at your low spot and loosely back filled, who knows. I doubt that a noticeable large "settlement" was only due to shrinkage.

Even if you do not have a test boring done, why not get some soil samples and check the moisture content? A post hole digger can get down a ways, but also some garden shops have small diameter augers that can be attached to lengths of threaded pipe (1/2" is common) for going deeper. Moisture content percentage is based upon the dry weight. Even rough weighing, as with a kitchen scale, can get you in the ball park. Off hand, any moisture content below 20 (as a guess for your area) and seeing that it is very hard digging, shoould be an indicator that shrinkage is likely at fault. The larger the sample, the less in the way of errors. Dry in an oven at 100C if possible or a little higher, over night. I am assuming you will find clay and not peat. Peat would be another whole different situation. Getting a geotech firm would be good, but may be more costly than you want as a start.

A concrete slab nearby likely means nothing.

As to the slope of the floor, it is surprising what people don't recognizes as "out of level". That's why cook stoves have adjustable feet. A convenience store gas station here (over a peat bog)had a difference in elevation from front to back of about a foot in 30 feet, yet they stayed in business for quite a while. I once measured the tilt of a liquor store at about 8 degrees, with bottles still stable on shelves!!!

 

[jayrod12]

My office is located in Winnipeg,

Welcome to Manitoba Gumbo, one of the only clays to have it's own name. Depending on the area of town some areas were highly treed prior to development and so the homes experience settlement the first few years after the trees were cleared off. To be honest the removal of trees generally results in rebound and not shrinkage but not always.

If you just want to re-level the house and not go so far as underpinning the house there is a (or multiple) company that inject expanding polyurethane into the soil below the house. This helps consolidate the soil if it was an original compaction issue that is still causing problems and it will lift the house as required.

Think of it the same as mudd ruckers but it's not mud that is injected it's a polymer formula that hardens and will not wash away with groundwater movement.

We have had success using this on a larger job where the marble staircase had sunk in comparison to the rest of the building. We have also used this in areas where there is localized soil failure.

The company we have dealt with the most is Polymor Canada (not 100% on spelling). They also showed us previous projects they've done where they re-levelled on of those slab on grade houses on Ness Ave. It was pretty slick.

 

[kgold]

Jay, I'm definitely interested in the expanding polymer. I've read about it but wasn't sure as to its effectiveness or availability in Winnipeg. Can you give me any more suggestions? Do you have a ballpark figure on the cost, and do you think there is a warranty or guarantee on the outcome? Will they do testing of the soil to help determine if their product is a feasible solution?

I'm getting a couple quotes tomorrow on the underpinning job but I think that's gonna be overkill and far too expensive. However, given the surface area of the footings that have dropped I'm a little nervous the polymer resin injection will be out of my price range as well.

I don't think I can get too close to this corner for a soil test this year without busting up that pad. Still, I may call a Geo in for a visit and maybe they'll have a plan of attack. However based on what my fellow Winnipeger is saying, it does sound like a clay issue from the first 10 years or so of the house.

 

[oldestguy]

Kgold:

Are you leaving the tree? Are you sure that expansion will not occur naturally and bring it back up?

As to a soil test, it is not just a little area that has been affected. Any test hole between the tree and the house will tell a lot. Even a test hole in another direction, the same distance from the tree will help in a decision. These conditions usually cover broad areas. They also can go very deep, especially below houses.

If you want to consider a treatment, in Texas it is common to inject hydrated lime to change the mineralogy of the expansive clay. Raising up the foundations is not the same.

Yours is not a simple situation.

 

[jayrod12]

Kgold,

Unfortunately I could not even begin to quote the costs for the expanding polymer. The guys at polymor would come out and take a look and give a quote for free I'm sure, that's what they did on the other couple of jobs. I know for a fact it is significantly cheaper than underpinning.

And besides, if you aren't underpinning the whole foundation then you are probably going to cause more harm then good. If you only underpin the one corner that is a problem, the rest of the house will move up and down with the seasons and you will see more significant cracking in the finishes.

Our company never underpins a portion of the foundation for this reason. In Winnipeg, houses on footings are expected to have seasonal movement however ideally the whole house moves as a unit (for the most part) as long as the base of the foundation was prepared properly and is on a "uniform" clay deposit. Big problems arise when you mix foundation types as friction piles will theoretically not move and the footing will and the building tears itself apart. We've specified lots of fixes for that exact issue.

Honestly, if you are getting the underpinning guys out, (Saber, Abalon, etc) call polymor to come take a look. And if you're pricing underpinning I hope you've called both of those two I mentioned, and maybe Shane Pedersen Construction.

Good luck,

 

[oldestguy]

Kgold appears to have good background experience on these things.

If one underpins, how deep does he go to by-pass the "moving" layer? I've seen dust dry clay soil in soil at basement levels and deeper. Even transferring support to piles may not cure things.

As this is going, I think you would be wise to have the advice of well experienced geotechnical engineers. Otherwise you could be creating an even worse situation in the long run. Check their credentials ans ask for references of jobs fixed.

 

[jayrod12]

I agree with oldestguy, a geotech's opinion would help.

That being said, Winnipeg clay is fairly homogenous (in a way). The depth varies greatly even over short distances but the quality of the clay is consistent and the moisture content is also fairly consistent.

In Winnipeg the geotechs that I've dealt with don't recommend piles that are shorter than 20 feet, 25 depending on which geotech you are talking to. If you ask a contractor they'll tell you 10 foot piles are enough.

It's not a case of by-passing the moving layer (as the clay layer here can go from 10 feet thick to 60 feet thick so there's no by-passing), it's a case of providing enough skin friction both downward and upward to keep the building in place. Or you can get a soils report and if till is close (10-15 feet) you could look at doing end-bearing piles (caissons).

In the end there are many ways you can go about "fixing" the problem. It just comes down to what you are going to consider fixed. If a level house is all you are looking for but can deal with slight seasonal movement then that can be accomplished via the "mud" jacking route (or polymer jacking). If you are looking to relevel and stop any future movement then a more extensive and expensive repair is needed, i.e. underpinning.

The issue you are going to run into with underpinning is there is not an easy way of making the house level prior to underpinning. They could lift the house off of the foundation easy enough but the foundation walls are not so easy. You could lift the house, remove the current foundation and then install a new piled foundation system but depending on the size of your house that could run you over $60k. Underpinning of the house will probably run you around $30k, assuming they underpin the whole foundation, and that doesn't even account for attempted relevelling of the house/foundation it is strictly for installing the piles.

Kgold will have to decide himself what is the appropriate "fix" for the problem and then it is possible to discuss specifics.

And now that I just went and re-read the original post I just thought about the fact you called this a bi-level. What do you figure is the depth to underside of footing? Probably 4 or 5 feet. Typical frost depth in Winnipeg is 6-8 feet. If your parking pad is near the foundation that will drive the frost deeper causing more issues. So that could be a possible cause of these problems too.