Slab-on-grade levelness, house settling 1

[fred181]

What are common construction tolerances for slab-on-grade flooring for residential?

I have a fall of 1-3/8" over ~12.5 ft towards a corner of my house. Despite accompanying cracking in the drywall at this corner, I am told by the Home Builder's engineer, that this is not evidence of settling, and that it was probably built that way. They are recommending a "cosmetic" repair. Also I would note, that the grading of the soil at this part of the house is sloped upwards away from the house, such that water does not drain away. I am told this does not affect soil strength.

Seems to me that settling is likely the issue, am I crazy?

 

[jayrod12]

It may not be settling per se, theoretically the rest of the slab could be moving upwards.

But short answer, no you aren't crazy. And 1 3/8" drop over 12 feet is not within standard construction tolerances.

Get a second engineer to come out and give you a report. Forward it on to the builder and his engineer for comment.

Is this a newly built house?

 

[bones206]

Try to get the builder's engineer to put their statements in writing. If they are misleading you knowing full well that there is a drainage/settlement issue, that is grounds for a disciplinary review by the state licensing board, IMO.

 

[fred181]

The house is almost 5 years old. The cracking in the drywall appeared right at the start of year 4. I acknowledge that anything is possible, but to me the most likely answer seems to be that the house is settling.

I've also been told by a geotech that my soil is not moisture sensitive. It's red clay, typical for the area. My understanding of clay soils is that soil strength changes significantly with moisture condition. And it would seem quite important that the soil is graded to move water away from the house.

 

[jayrod12]

What your geotech told you is correct regarding strength of clay and moisture content. Soil strength in generally is typically quite dependent on moisture content regardless of soil type.

Again, hire a local, non-biased 3rd party structural engineer to come by and provide a report. Then have the builder and their engineer review it. Don't give up until you're satisfied with the answer (even if the answer isn't the one you were hoping for, they may still be able to explain their position in a way you deem acceptable even if unfortunate).

 

[phamENG]

What kind of cracks are we talking about? Hairlines, or can you stick a pen through them? A roughly 1% slope with hairline cracks...the builder's engineer may not be far off. How about the ceiling and/or floor above? If you set up a laser level and measure from a known level line to the ceiling, is it the same slope as the floor? If yes, then it sounds like differential settlement and the house may be leaning. They should also check the plumbness of the walls. If the house is leaning, the walls are likely out of plumb a bit, too. But if the floor is sloped and the ceiling or floor above is level, that would tell me that the slab was poured out of level and the framer compensated somehow and built the upper framing level.

I've understood typical slab tolerance to be maximum of .25" in 10ft...or 0.2%. So even if it was built that way, it was built way out. I can't point to anything definite though...might find something useful in ACI 117, but I don't have a copy.

Even if the builder's engineer is correct, you should certainly get another opinion. In theory they are impartial, but we're all human, and there are plenty of engineers out there more partial to their clients then to the strictest interpretation of the truth.

 

[fred181]

Jayrod12,

To be clear, the homebuilder's geotech told me the soil is NOT moisture sensitive. That is, not significantly affected by moisture content.

 

[phamENG]

fred181 - I'm guess all of these threads are related:

thread158-485240
thread765-485239

 

[jayrod12]

By that they mean it's not volumetrically sensitive to moisture, i.e. it doesn't expand or contract with changing moisture contents. The bearing capacity of the soil is still affected by changes in moisture content.

If you are getting what feels like the run-around from the builder's consultants, it's time to bring in your own consultants and have them comment.

Pham gave you some good ideas to determine whether it is the slab only, or other aspects of the house as well. Answers to his questions will help the rest of us form some opinions.

Some pictures of the damage, and maybe some from further away on the outside looking down each wall would likely help.

 

[fred181]

Yes, they are all very much related.

I have two adjacent corners of my house that are possibly/likely(?) settling. I have had a engineering tech from a structural firm and an E.I.T. from a geotech look at it. Both have made statements that are demonstrably untrue. I would like to come to a conclusion that makes good engineering sense. But these other "engineers" have me questioning my own judgement. It's been very helpful getting insight from other engineers here, with more expertise in this realm.

Ultimately, I may have to hire a 3rd party engineer or settle for fight for some extended warranty.

 

[phamENG]

Charlotte has several good structural engineers. I think a few of the members of this board practice in that area or nearby. I'm sure you can find one that will give you a thorough inspection. Just be prepared to pay for it. A really thorough investigation, analysis, and report from a reputable structural engineer could easily cost you upwards of $1000 or more. Some will do it for less, but the closer you are to a large metropolitan area the more expensive they are likely to be.

 

[Tomfh]

I agree that is well outside of tolerance. The cracking indicates movement. So it is lower than it should be, and it has moved, thus settlement is likely.

 

[bones206]

Isn’t positive slope away from the foundation a code requirement? I used to live in Charlotte and the 70 year old house I bought had slope/drainage issues in one corner and the settlement was quite apparent. As was the water literally shooting out of the CMU walls one time I predrilled a hole for a tapcon anchor! At the very least the builder should be on the hook for fixing that grade and making it code compliant. They should fix the slab too but good luck with that. My experience in the Charlotte area is that there is a lot of money to be made currently in the building sector and its attracted a lot of shady actors. There is a reason that mud jacking and helical pile companies are so active in that area…

 

[A.F]

Asking neighbours if the have similar issue
May help in total investigation/ especially soul type

 

[LittleInch]

Can you / have you lifted the floor covering in that room to see if the slab has cracked anywhere?

Is there any evidence that the slab has settled but not the outer walls? / gaps in the skirting board etc?

If its that much settlement can you see anything on the outside walls which are made of ??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dik]

Over prolonged drought, clays can be subject to shrinkage settlement... some clays, bigtime. Nearly all clays are subject to moisture movement, but due to their relative impermeability it doesn't happen... with highly plastic ones shrinkage, if it occurs, can be substantial.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[JoshPlumSE]

Despite accompanying cracking in the drywall at this corner, I am told by the Home Builder's engineer, that this is not evidence of settling, and that it was probably built that way. They are recommending a "cosmetic" repair. Also I would note, that the grading of the soil at this part of the house is sloped upwards away from the house, such that water does not drain away. I am told this does not affect soil strength.

Some quick thoughts on this:
1) Drywall cracks are common for small amounts of movement. Drywall is very brittle and this is often the only "damage" that will occur. So, this alone is not cause for concern.
2) Now, nearly 1.5" of differential movement over 12.5 ft. That's a different story.... That's quite a lot.

3) Something similar occurred with my house.
a) Original construction of my house was 1972. Some minor sloping in the neighborhood suggests some of my house was on engineered fill.
b) There was an addition added in 1982-ish. There is addition extended the house out maybe 8 feet in one direction. Well, the soil under the addition was on fill, but it was NOT the engineered fill that other parts of the house were built on.
c) As such, there was significant settlement of the slab. More than an inch over the, 8 feet or so of the addition.
d) Most of the settlement happened in the first few months during construction. BEFORE the drywall was placed.
e) Over the next few years (I bought the house in 2001) some more settlement occurred and the drywall cracked. Only a little bit. But, it really drew the attention of people who were interested in buying the house. So, it affected the price of the house.
f) After 3 to 5 years, any settlement of the house due to the weight of it on the soil is usually very minimal. So, I felt comfortable buying the house.
g) When we re-did the kitchen (10 years ago), we ripped out the drywall and replaced it.... drywall cracks haven't returned.
h) I also used some topping material over the slab to "level it out". I couldn't level the whole amount out, but it's much, much less noticeable.
i) I also replace the tile flooring with hard wood flooring (which is much less sensitive to movement).​

I mention my experience because even when something APPEARS to be a huge problem, a simple / cosmetic fix can be a valid solution. In your case, I don't know for sure. I'd want to understand the root cause of the movement. Is it settlement that occurred mostly during construction (and before the drywall was placed) like it was for my house? That merely cracked drywall slightly as the last little bits of settlement were squeezed out of the soil? Or, was there a different event that caused this? Moisture infiltration, broken pipe, et cetera.